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Articoli di riviste sul tema "Photodissociation Region"

Autore: Grafiati

Pubblicato: 2 novembre 2024

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1

Tielens, A. G. G. M., e D. Hollenbach. "Photodissociation Regions - Part Two - a Model for the Orion Photodissociation Region". Astrophysical Journal 291 (aprile 1985): 747. http://dx.doi.org/10.1086/163112.

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2

Tielens, A. G. G. M., e D. Hollenbach. "Photodissociation regions. I - Basic model. II - A model for the Orion photodissociation region". Astrophysical Journal 291 (aprile 1985): 722. http://dx.doi.org/10.1086/163111.

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3

Klein, Randolf, Alexander Reedy, Christian Fischer, Leslie W. Looney, Sebastian Colditz, Dario Fadda, Alexander G. G. M. Tielens e Willam D. Vacca. "The Photodissociation and Ionization Fronts in M17-SW Localized with FIFI-LS on Board SOFIA". Astrophysical Journal 945, n. 1 (1 marzo 2023): 29. http://dx.doi.org/10.3847/1538-4357/acb823.

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Abstract To understand star formation rates, studying feedback mechanisms that regulate star formation is necessary. The radiation emitted by nascent massive stars play a significant role in feedback by photodissociating and ionizing their parental molecular clouds. To gain a detailed picture of the physical processes, we mapped the photodissociation region (PDR) M17-SW in several fine-structure and high-J CO lines with FIFI-LS, the far-infrared imaging spectrometer aboard SOFIA. An analysis of the CO and [O i]146 μm line intensities, combined with the far-infrared intensity, allows us to create a density and UV intensity map using a one-dimensional model. The density map reveals a sudden change in the gas density crossing the PDR. The strengths and limits of the model and the locations of the ionization and photodissociation front of the edge-on PDR are discussed.

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4

Escalante, V., e A. Góngora-T. "Photodissociation Regions in Planetary Nebulae". Symposium - International Astronomical Union 155 (1993): 220. http://dx.doi.org/10.1017/s0074180900170822.

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The photodissociation rate of H2 molecules by UV photons from PN central stars is generally several orders of magnitude larger than the rate produced by the average interstellar field (Sternberg 1988, Escalante et al. 1991). Thus, in neutral envelopes of PN's, H2 molecules are destroyed quickly, and a photodissociation region forms around ionization bounded nebulae. Observations of H2 in PN's reveal that not all the hydrogen is photodissociated, and it has been suggested that this is due to the existence of dense disks around the ionized region (Zuckerman and Gatley 1988).

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5

Bisbas, Thomas G., Jonathan C. Tan e Kei E. I. Tanaka. "Photodissociation region diagnostics across galactic environments". Monthly Notices of the Royal Astronomical Society 502, n. 2 (15 gennaio 2021): 2701–32. http://dx.doi.org/10.1093/mnras/stab121.

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ABSTRACT We present three-dimensional astrochemical simulations and synthetic observations of magnetized, turbulent, self-gravitating molecular clouds. We explore various galactic interstellar medium environments, including cosmic ray ionization rates in the range of ζCR = 10−17–$10^{-14}\, {\rm s}^{-1}$, far-UV intensities in the range of G0 = 1–103 and metallicities in the range of Z = 0.1–$2\, {\rm Z}_{\odot }$. The simulations also probe a range of densities and levels of turbulence, including cases where the gas has undergone recent compression due to cloud–cloud collisions. We examine: (i) the column densities of carbon species across the cycle of C ii, C i, and CO, along with O i, in relation to the H i-to-H2 transition; (ii) the velocity-integrated emission of [C ii] 158 μm, [13C ii] 158 μm, [C i] 609 μm and 370 μm, [O i] 63 μm and 146 μm, and of the first ten 12CO rotational transitions; (iii) the corresponding Spectral Line Energy Distributions; (iv) the usage of [C ii] and [O i] 63 μm to describe the dynamical state of the clouds; (v) the behaviour of the most commonly used ratios between transitions of CO and [C i]; and (vi) the conversion factors for using CO and C i as H2-gas tracers. We find that enhanced cosmic ray energy densities enhance all aforementioned line intensities. At low metallicities, the emission of [C ii] is well connected with the H2 column, making it a promising new H2 tracer in metal-poor environments. The conversion factors of XCO and XC i depend on metallicity and the cosmic ray ionization rate, but not on FUV intensity. In the era of ALMA, SOFIA, and the forthcoming CCAT-prime telescope, our results can be used to understand better the behaviour of systems in a wide range of galactic and extragalactic environments.

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6

Tielens, A. G. G. M. "Photodissociation Regions and Planetary Nebulae". Symposium - International Astronomical Union 155 (1993): 155–62. http://dx.doi.org/10.1017/s0074180900170330.

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FUV photons (<13.6eV) from the central star create a region of warm (≈1000K) atomic and molecular gas around Planetary Nebulae (PN). This paper reviews theoretical and observational characteristics of such regions, commonly called photodissociation regions or PDRs. PDRs around PN differ in some aspects from those in other galactic objects and this is briefly discussed with an emphasis on time dependent effects. It is concluded that, in evolved PN (texp>103 yr), molecules will only survive inside dense clumps (>106 cm−3). H2 emission from such dense gas will show a thermal spectrum in the low v states. Finally, the physical conditions in the PDR associated with NGC 7027 are compared to those in other galactic and extragalactic PDRs

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7

Hartquist, T. W., e A. Sternberg. "Photodissociation-region models of interstellar hydroxyl masers". Monthly Notices of the Royal Astronomical Society 248, n. 1 (gennaio 1991): 48–51. http://dx.doi.org/10.1093/mnras/248.1.48.

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8

Pellegrini, E. W., J. A. Baldwin, C. L. Brogan, M. M. Hanson, N. P. Abel, G. J. Ferland, H. B. Nemala, G. Shaw e T. H. Troland. "A Magnetically Supported Photodissociation Region in M17". Astrophysical Journal 658, n. 2 (aprile 2007): 1119–35. http://dx.doi.org/10.1086/511258.

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9

Guzmán, Viviana V., Jérôme Pety, Pierre Gratier, Javier R. Goicoechea, Maryvonne Gerin, Evelyne Roueff, Franck Le Petit e Jacques Le Bourlot. "Chemical complexity in the Horsehead photodissociation region". Faraday Discuss. 168 (2014): 103–27. http://dx.doi.org/10.1039/c3fd00114h.

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The interstellar medium is known to be chemically complex. Organic molecules with up to 11 atoms have been detected in the interstellar medium, and are believed to be formed on the ices around dust grains. The ices can be released into the gas-phase either through thermal desorption, when a newly formed star heats the medium around it and completely evaporates the ices; or through non-thermal desorption mechanisms, such as photodesorption, when a single far-UV photon releases only a few molecules from the ices. The first mechanism dominates in hot cores, hot corinos and strongly UV-illuminated PDRs, while the second dominates in colder regions, such as low UV-field PDRs. This is the case of the Horsehead were dust temperatures are ≃20–30 K, and therefore offers a clean environment to investigate the role of photodesorption. We have carried out an unbiased spectral line survey at 3, 2 and 1mm with the IRAM-30m telescope in the Horsehead nebula, with an unprecedented combination of bandwidth, high spectral resolution and sensitivity. Two positions were observed: the warm PDR and a cold condensation shielded from the UV field (dense core), located just behind the PDR edge. We summarize our recently published results from this survey and present the first detection of the complex organic molecules HCOOH, CH₂CO, CH₃CHO and CH₃CCH in a PDR. These species together with CH₃CN present enhanced abundances in the PDR compared to the dense core. This suggests that photodesorption is an efficient mechanism to release complex molecules into the gas-phase in far-UV illuminated regions.

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10

Federman, S. R., D. C. Knauth, David L. Lambert e B‐G Andersson. "Probing the Photodissociation Region toward HD 200775". Astrophysical Journal 489, n. 2 (10 novembre 1997): 758–65. http://dx.doi.org/10.1086/304804.

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11

Bisbas, T. G., T. A. Bell, S. Viti, M. J. Barlow, J. Yates e M. Vasta. "A photodissociation region study of NGC 4038". Monthly Notices of the Royal Astronomical Society 443, n. 1 (9 luglio 2014): 111–21. http://dx.doi.org/10.1093/mnras/stu1143.

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12

Kawakita, Hideyo. "Photodissociation Rate, Excess Energy, and Kinetic Total Energy Release for the Photolysis of H₂O Producing O(¹S) by Solar UV Radiation Field". Astrophysical Journal 931, n. 1 (1 maggio 2022): 24. http://dx.doi.org/10.3847/1538-4357/ac67e2.

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Abstract Forbidden atomic oxygen lines in emission are ubiquitous for cometary spectra in the visible region, and the oxygen atoms in metastable states causing the forbidden emission lines are considered as a proxy of H2O in coma. However, the photodissociation rate and related quantities for the dissociation reaction producing O(1S) from H2O have never been estimated based on experimental studies. Based on the recent laboratory study of the photodissociation reaction of H2O producing O(1S) by Chang et al., we derived the photodissociation rates of the reactions for both the O(1S) and O(1D) channels, consistent with the green-to-red line ratios observed in comets so far. Furthermore, the total kinetic energies released for the photodissociation products are also consistent with the intrinsic line widths of forbidden atomic oxygen emission lines observed in comets. The photodissociation rates of H2O leading to O(1S) and O(1D) calculated here do not significantly change the previous estimates of CO2/H2O in comets based on the green-to-red line ratios of the comets if we use the photodissociation rates of CO2 (calculated elsewhere) with a correction for the difference of solar UV spectra used for calculating photodissociation rates of H2O and CO2.

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13

Tiwari, M., K. M. Menten, F. Wyrowski, J. P. Pérez-Beaupuits, H. Wiesemeyer, R. Güsten, B. Klein e C. Henkel. "Unveiling the remarkable photodissociation region of Messier 8". Astronomy & Astrophysics 615 (luglio 2018): A158. http://dx.doi.org/10.1051/0004-6361/201732437.

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Aims. Messier 8 (M8) is one of the brightest HII regions in the sky. We collected an extensive dataset comprising multiple sub- millimeter spectral lines from neutral and ionized carbon and from CO. Based on this dataset, we aim to understand the morphology of M8 and that of its associated photodissociation region (PDR) and to carry out a quantitative analysis of the physical conditions of these regions such as kinetic temperatures and volume densities. Methods. We used the Stratospheric Observatory For Infrared Astronomy (SOFIA), the Atacama Pathfinder Experiment (APEX) 12 m, and the Institut de Radioastronomie Millimétrique (IRAM) 30 m telescopes to perform a comprehensive imaging survey of the emission from the fine structure lines of [C II] and [C I] and multiple rotational transitions of carbon monoxide (CO) isotopologs within 1.3 × 1.3 pc around the dominant Herschel 36 (Her 36) system, which is composed of at least three massive stars. To further explore the morphology of the region, we compared archival infrared, optical, and radio images of the nebula with our newly obtained fine structure line and CO data, and in particular with the velocity information these data provide. We performed a quantitative analysis, using both LTE and non-LTE methods to determine the abundances of some of the observed species, kinetic temperatures, and volume densities. Results. Bright CO, [C II] and [C I] emission have been found toward the HII region and the PDR in M8. Our analysis places the bulk of the molecular material in the background of the nebulosity illuminated by the bright stellar systems Her 36 and 9 Sagitarii. Since the emission from all observed atomic and molecular tracers peaks at or close to the position of Her 36, we conclude that the star is still physically close to its natal dense cloud core and heats it. A veil of warm gas moves away from Her 36 toward the Sun and its associated dust contributes to the foreground extinction in the region. One of the most prominent star forming regions in M8, the Hourglass Nebula, is particularly bright due to cracks in this veil close to Her 36. We obtain H2 densities ranging from ~104–106 cm–3 and kinetic temperatures of 100–150 K in the bright PDR caused by Her 36 using radiative transfer modeling of various transitions of CO isotopologs.

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14

White, Glenn J., e Rachael Padman. "Observations of Atomic Gas in Photodissociation Regions". Symposium - International Astronomical Union 150 (1992): 297–302. http://dx.doi.org/10.1017/s0074180900090203.

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At the interface between an HII region and a molecular cloud, lies a neutral gas layer which is subject to both an intense radiation field, and to shocks arising from the expansion of the ionisation front of the HII region. The gas in these regions is highly excited, hot, and may be fairly dense. We present the first high resolution images of atomic carbon towards a sample of ionisation front sources. This study has relevance to our understanding of shock induced star formation, the formation and destruction of molecular species under extreme conditions, shock processes in the ISM, and the energy balance in molecular clouds.

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15

Henney, William J. "Raman mapping of photodissociation regions". Monthly Notices of the Royal Astronomical Society 502, n. 3 (29 gennaio 2021): 4597–616. http://dx.doi.org/10.1093/mnras/stab257.

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ABSTRACT Broad Raman-scattered wings of hydrogen lines can be used to map neutral gas illuminated by high-mass stars in star-forming regions. Raman scattering transforms far-ultraviolet starlight from the wings of the Lyβ line (1022–1029 Å) to red visual light in the wings of the Hα line (6400 –6700 Å). Analysis of spatially resolved spectra of the Orion Bar and other regions in the Orion Nebula shows that this process occurs in the neutral photodissociation region between the ionization front and dissociation front. The inner Raman wings are optically thick and allow the neutral hydrogen density to be determined, implying $n(\mathrm{H^0}) \approx 10^5\, \mathrm{cm}^{-3}$ for the Orion Bar. Far-ultraviolet resonance lines of neutral oxygen imprint their absorption on to the stellar continuum as it passes through the ionization front, producing characteristic absorption lines at 6633 Å and 6664 Å with widths of order 2 Å. This is a unique signature of Raman scattering, which allows it to be easily distinguished from other processes that might produce broad Hα wings, such as electron scattering or high-velocity outflows.

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16

Kuusik, I., M. Tarkanovskaja, J. Kruusma, V. Reedo, R. Välbe, A. Lõhmus, V. Kisand, E. Lust, E. Kukk e E. Nõmmiste. "Near threshold photodissociation study of EMIMBF4 vapor". RSC Advances 5, n. 9 (2015): 6834–42. http://dx.doi.org/10.1039/c4ra12775g.

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17

Gejo, T., K. Okada, T. Ibuki e N. Saito. "Photodissociation of Ozone in the K Edge Region". Journal of Physical Chemistry A 103, n. 24 (giugno 1999): 4598–601. http://dx.doi.org/10.1021/jp9904670.

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18

Farooq, Zahid, Dimitri A. Chestakov, Bin Yan, Gerrit C. Groenenboom, Wim J. van der Zande e David H. Parker. "Photodissociation of singlet oxygen in the UV region". Physical Chemistry Chemical Physics 16, n. 7 (2014): 3305. http://dx.doi.org/10.1039/c3cp54696a.

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19

Okada, Y., R. Güsten, M. A. Requena-Torres, M. Röllig, P. Hartogh, H. W. Hübers, T. Klein, O. Ricken, R. Simon e J. Stutzki. "Dynamics and photodissociation region properties in IC 1396A". Astronomy & Astrophysics 542 (10 maggio 2012): L10. http://dx.doi.org/10.1051/0004-6361/201218911.

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20

Ji, Lei, Ying Tang, Rongshu Zhu, Bifeng Tang e Bing Zhang. "Studies on photodissociation of dibromoalkane in UV region". Chemical Physics 314, n. 1-3 (luglio 2005): 173–78. http://dx.doi.org/10.1016/j.chemphys.2005.03.002.

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21

Kanda, Kazuhiro, Shunji Katsumata, Takashi Nagata, Yasushi Ozaki, Tamotsu Kondow, Kozo Kuchitsu, Atsunari Hiraya e Kosuke Shobatake. "Photodissociation of BrCN in the vacuum ultraviolet region". Chemical Physics 175, n. 2-3 (settembre 1993): 399–411. http://dx.doi.org/10.1016/0301-0104(93)85168-8.

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22

Matsumi, Yutaka, Masahiro Kawasaki, Tetsuya Sato, Tohoru Kinugawa e Tatsuo Arikawa. "Photodissociation of chlorine molecule in the UV region". Chemical Physics Letters 155, n. 4-5 (marzo 1989): 486–90. http://dx.doi.org/10.1016/0009-2614(89)87191-x.

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23

Shamsuddin, Sayed Mohammed, Yousuke Inagaki, Yutaka Matsumi e Masahiro Kawasaki. "O(3Pj) atom formation from photodissociation of ozone in the visible and ultraviolet region". Canadian Journal of Chemistry 72, n. 3 (1 marzo 1994): 637–42. http://dx.doi.org/10.1139/v94-088.

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The photodissociation of ozone at 266, 308, and 532 nm has been studied for [Formula: see text] probing O(3Pj) atomic photofragments by a vacuum ultraviolet laser-induced fluorescence method. Angular distributions and average kinetic energies are determined by measuring Doppler profiles of the O(3Pj) photofragments. Anisotropy parameters β for the angular distributions are 0.81 ± 0.10 at 266 nm, 0.60 ± 0.10 at 308 nm, and −0.68 ± 0.09 at 532 nm. These values are consistent with the assignment of the photoexcited states, that is, 1B2 in the ultraviolet and 1B1 in the visible region. Average center-of-mass translational energies are 44, 38, and 21 kcal/mol for photodissociation at 266, 308, and 532 nm, respectively. The j-branching ratios of O(3Pj) produced from the photodissociation at 266 nm are (j = 2)/(j = 1)/(j = 0) = (0.55 ± 0.03)/(0.32 ± 0.03)/(0.12 ± 0.03), which are close to the state degeneracy (2j + 1) ratios. At 308 and 532 nm the branching ratios are (j = 2)/(j = 1)/(j = 0) = (0.66 ± 0.03)/(0.27 ± 0.03)/(0.09 ± 0.01) and (0.74 ± 0.03)/(0.20 ± 0.02)/(0.05 ± 0.01), respectively. Population of the j = 2 level increases with decreasing photon energies. The ratios obtained are discussed in terms of the adiabaticity of the potential surfaces during bond breakup as a function of the relative speed of separation.

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24

Figueira, M., A. Zavagno, L. Bronfman, D. Russeil, R. Finger e F. Schuller. "APEX CO observations towards the photodissociation region of RCW 120". Astronomy & Astrophysics 639 (luglio 2020): A93. http://dx.doi.org/10.1051/0004-6361/202037713.

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Context. The edges of ionized (H II) regions are important sites for the formation of (high-mass) stars. Indeed, at least 30% of the Galactic high-mass-star formation is observed there. The radiative and compressive impact of the H II region could induce star formation at the border following different mechanisms such as the collect and collapse or the radiation-driven implosion (RDI) models and change their properties. Aims. We aim to study the properties of two zones located in the photo dissociation region (PDR) of the Galactic H II region RCW 120 and discuss them as a function of the physical conditions and young star contents found in both clumps. Methods. Using the APEX telescope, we mapped two regions of size 1.5′ × 1.5′ toward the most massive clump of RCW 120 hosting young massive sources and toward a clump showing a protrusion inside the H II region and hosting more evolved low-mass sources. The 12CO (J = 3−2), 13CO (J = 3−2) and C18O (J = 3−2) lines observed, together with Herschel data, are used to derive the properties and dynamics of these clumps. We discuss their relation with the hosted star formation. Results. Assuming local thermodynamic equilibrium, the increase of velocity dispersion and Tex are found toward the center of the maps, where star-formation is observed with Herschel. Furthermore, both regions show supersonic Mach numbers (7 and 17 in average). No substantial information has been gathered about the impact of far ultraviolet radiation on C18O photodissociation at the edges of RCW 120. The fragmentation time needed for CC to be at work is equivalent to the dynamical age of RCW 120 and the properties of region B are in agreement with bright-rimmed clouds. Conclusions. Although conclusions from this fragmentation model should be taken with caution, it strengthens the fact that, together with evidence of compression, CC might be at work at the edges of RCW 120. Additionally, the clump located at the eastern part of the PDR is a good candidate pre-existing clump where star-formation may be induced by the RDI mechanism.

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Hasegawa, Tetsuo. "Molecular Hydrogen Emission from Photodissociation Regions". International Astronomical Union Colloquium 120 (1989): 24–31. http://dx.doi.org/10.1017/s0252921100023447.

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AbstractWe review new observational and theoretical developments of the understanding of the H2 infrared emission in the last 5 years since the discovery of the fluorescent emission in NGC 2023. An excitation analysis of H2 in a variety of Galactic sources has revealed that in many sources the excitation is expressed as a mixture of thermal and fluorescent components. This finding is in good agreement with theories of photodissociation regions, in which the population of H2 changes its character from pure fluorescence to thermal as the density of the region increases. The ortho/para abundance ratio of the fluorescent H2 is observed to lie within a limited range of 1.1 — 1.8 which is well reproduced by depth-dependent model calculations of the ultraviolet excitation and dissociation of H2 molecules. This may be understood as due to the independent self shielding of each of the ortho- and para-H2, rather than the ortho/para abundance ratio of the predissociated H2, a low formation temperature of H2 on grains, or gas phase interchange reactions. A laser emission of molecular hydrogen discovered in the planetary nebula NGC7027 further demonstrates the nonthermal nature of the H2 emission in photodissociation regions.

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Roehl, C. M., Z. Marka, J. L. Fry e P. O. Wennberg. "Near-UV photolysis cross sections of CH<sub>3</sub>OOH and HOCH<sub>2</sub>OOH determined via action spectroscopy". Atmospheric Chemistry and Physics Discussions 6, n. 6 (20 novembre 2006): 11597–620. http://dx.doi.org/10.5194/acpd-6-11597-2006.

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Abstract. Knowledge of molecular photolysis cross sections is important for determining atmospheric lifetimes and fates of many species. A method and laser apparatus for measurement of these cross sections in the near-ultraviolet (UV) region is described. The technique is based on action spectroscopy, where the yield of a photodissociation product (in this case OH) is measured as a function of excitation energy. For compounds yielding OH, this method can be used to measure near-UV photodissociation cross section as low as 10−23 cm2 molecule−1. The method is applied to determine the photodissociation cross sections for methyl hydroperoxide (CH3OOH; MHP) and hydroxymethyl hydroperoxide (HOCH2OOH; HMHP) in the 305–365 nm wavelength range. The measured cross sections are in good agreement with previous measurements of absorption cross sections.

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Roehl, C. M., Z. Marka, J. L. Fry e P. O. Wennberg. "Near-UV photolysis cross sections of CH<sub>3</sub>OOH and HOCH<sub>2</sub>OOH determined via action spectroscopy". Atmospheric Chemistry and Physics 7, n. 3 (14 febbraio 2007): 713–20. http://dx.doi.org/10.5194/acp-7-713-2007.

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Abstract. Knowledge of molecular photolysis cross sections is important for determining atmospheric lifetimes and fates of many species. A method and laser apparatus for measurement of these cross sections in the near-ultraviolet (UV) region is described. The technique is based on action spectroscopy, where the yield of a photodissociation product (in this case OH) is measured as a function of excitation energy. For compounds yielding OH, this method can be used to measure near-UV photodissociation cross section as low as 10−23 cm2 molecule−1. The method is applied to determine the photodissociation cross sections for methyl hydroperoxide (CH3OOH; MHP) and hydroxymethyl hydroperoxide (HOCH2OOH; HMHP) in the 305–365 nm wavelength range. The measured cross sections are in good agreement with previous measurements of absorption cross sections.

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Stachoň, Martin, Aleš Vítek e René Kalus. "Photodissociation of medium-sized argon cluster cations in the visible region". Physical Chemistry Chemical Physics 17, n. 48 (2015): 32413–24. http://dx.doi.org/10.1039/c5cp05257b.

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Semiclassical methods for non-adiabatic dynamics simulations, based on a semiempirical diatomics-in-molecules model of intracluster interactions and the mean-field dynamical approach with the inclusion of quantum decoherence, have been used to study the photodissociation of argon cluster cations, Ar_N⁺ (N = 6–19), at E_phot = 2.35 eV.

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Ohashi, Kazuhiko, Yasuhiro Nakai, Takeshi Shibata e Nobuyuki Nishi. "Photodissociation Spectroscopy of (C6H6)2+". Laser Chemistry 14, n. 1-3 (1 gennaio 1994): 3–14. http://dx.doi.org/10.1155/1994/52450.

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The photodissociation spectrum of (C6H6)2+ is obtained from the yields of fragment C6H6+ ion as a function of photodissociation wavelength in the 400–1400 nm region. Two bands at 440 and 580 nm are attributed to the C ← X and the B ← X local excitation (LE) bands, respectively. Both the most intense band at 920 nm and relatively weak one at 1160 nm are assigned to charge resonance (CR) bands. The red-shift of the B ← X band from that of C6H6+ and the cross sections at the CR bands much larger than those at the LE bands are consistent with a sandwich structure for (C6H6)2+. The appearance of the two CR bands is explained on the basis of displaced sandwich structures for (C6H6)2+.

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Habart, E., E. Dartois, A. Abergel, J. P. Baluteau, D. Naylor, E. Polehampton, C. Joblin et al. "SPIRE spectroscopy of the prototypical Orion Bar photodissociation region". Astronomy and Astrophysics 518 (luglio 2010): L116. http://dx.doi.org/10.1051/0004-6361/201014654.

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31

Tielens, A. G. G. M., M. M. Meixner, P. P. van der Werf, J. Bregman, J. A. Tauber, J. Stutzki e D. Rank. "Anatomy of the Photodissociation Region in the Orion Bar". Science 262, n. 5130 (1 ottobre 1993): 86–89. http://dx.doi.org/10.1126/science.262.5130.86.

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32

Steiman‐Cameron, Thomas Y., Michael R. Haas, A. G. G. M. Tielens e Michael G. Burton. "Physical Conditions in the Photodissociation Region of NGC 2023". Astrophysical Journal 478, n. 1 (20 marzo 1997): 261–70. http://dx.doi.org/10.1086/303759.

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33

Kanda, Kazuhiro, Mitsuhiko Kono, Takashi Nagata, Atsunari Hiraya, Kiyohiko Tabayashi e Kosuke Shobatake. "Photodissociation spectroscopy of ClCN in the vacuum ultraviolet region". Chemical Physics 255, n. 2-3 (maggio 2000): 369–78. http://dx.doi.org/10.1016/s0301-0104(00)00064-1.

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34

Kanda, Kazuhiro, Shunji Katsumata, Takashi Nagata, Tamotsu Kondow, Atsunari Hiraya, Kiyohiko Tabayashi e Kosuke Shobatake. "Photodissociation spectroscopy of ICN in the vacuum ultraviolet region". Chemical Physics 218, n. 1-2 (maggio 1997): 199–209. http://dx.doi.org/10.1016/s0301-0104(97)00033-5.

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35

Zhu, Lei, e Thomas J. Cronin. "Photodissociation of benzaldehyde in the 280–308 nm region". Chemical Physics Letters 317, n. 3-5 (febbraio 2000): 227–31. http://dx.doi.org/10.1016/s0009-2614(99)01375-5.

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36

Sumida, Masataka, Takuya Hanada, Katsuyoshi Yamasaki e Hiroshi Kohguchi. "Photodissociation dynamics of C3H5I in the near-ultraviolet region". Journal of Chemical Physics 141, n. 10 (14 settembre 2014): 104316. http://dx.doi.org/10.1063/1.4894393.

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37

Brooks, K. J., P. Cox, N. Schneider, J. W. V. Storey, A. Poglitsch, N. Geis e L. Bronfman. "The Trumpler 14 photodissociation region in the Carina Nebula". Astronomy & Astrophysics 412, n. 3 (dicembre 2003): 751–65. http://dx.doi.org/10.1051/0004-6361:20031406.

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38

Levenson, N. A., James R. Graham, Ian S. McLean, E. E. Becklin, Donald F. Figer, Andrea M. Gilbert, James E. Larkin, Harry I. Teplitz e Mavourneen K. Wilcox. "Hot Stars and Cool Clouds: The Photodissociation Region M16". Astrophysical Journal 533, n. 1 (10 aprile 2000): L53—L56. http://dx.doi.org/10.1086/312601.

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39

Wei, Zheng-Rong, Xiao-Peng Zhang, Wei-Bin Lee, Bing Zhang e King-Chuen Lin. "Photodissociation dynamics of propionyl chloride in the ultraviolet region". Journal of Chemical Physics 130, n. 1 (7 gennaio 2009): 014307. http://dx.doi.org/10.1063/1.3012353.

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40

Pound, Marc W., e Mark G. Wolfire. "The PhotoDissociation Region Toolbox: Software and Models for Astrophysical Analysis". Astronomical Journal 165, n. 1 (20 dicembre 2022): 25. http://dx.doi.org/10.3847/1538-3881/ac9b1f.

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Abstract (sommario):

Abstract The PhotoDissociation Region Toolbox provides comprehensive, easy-to-use, public software tools and models that enable an understanding of the interaction of the light of young, luminous, massive stars with the gas and dust in the Milky Way and in other galaxies. It consists of an open-source Python toolkit and photodissociation region (PDR) models for analysis of infrared and millimeter/submillimeter line and continuum observations obtained by ground-based and suborbital telescopes, and astrophysics space missions. PDRs include all of the neutral gas in the interstellar medium where far-ultraviolet photons dominate the chemistry and/or heating. In regions of massive star formation, PDRs are created at the boundaries between the H ii regions and neutral molecular cloud, as photons with energies 6 eV < h ν < 13.6 eV photodissociate molecules and photoionize metals. The gas is heated by photoelectrons from small grains and large molecules and cools mostly through far-infrared (FIR) fine-structure lines like [O i] and [C ii]. The models are created from state-of-the art PDR codes that include molecular freeze-out; recent collision, chemical, and photorates; new chemical pathways, such as oxygen chemistry; and allow for both clumpy and uniform media. The models predict the emergent intensities of many spectral lines and FIR continuum. The tools find the best-fit models to the observations and provide insight into the physical conditions and chemical makeup of the gas and dust. The PDR Toolbox enables novel analysis of data from telescopes such as the Infrared Space Observatory, Spitzer, Herschel, the Stratospheric Terahertz Observatory, the Stratospheric Observatory for Infrared Astronomy, the Submillimeter Wave Astronomy Satellite, the Atacama Pathfinder Experiment, the Atacama Large Millimeter/submillimeter Array, and the JWST.

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41

Chen, Yinjuan, Ke Xin, Jiaye Jin, Wei Li, Qiang Wang, Xuefeng Wang e Guanjun Wang. "Infrared photodissociation spectroscopic investigation of TMO(CO)n+ (TM = Sc, Y, La): testing the 18-electron rule". Physical Chemistry Chemical Physics 21, n. 12 (2019): 6743–49. http://dx.doi.org/10.1039/c8cp07748g.

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Abstract (sommario):

Gaseous TMO(CO)_n⁺ (TM = Sc, Y, La) complex cations prepared via laser vaporization were mass-selected and studied by infrared photodissociation spectroscopy in the C–O stretching frequency region.

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42

Hester, J. J. "Life at the edge - Emission from the H II region/photodissociation region interface". Publications of the Astronomical Society of the Pacific 103 (agosto 1991): 853. http://dx.doi.org/10.1086/132893.

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43

An, Suming, Sukrit Ranjan, Kaijun Yuan, Xueming Yang e Rex T. Skodje. "The role of the three body photodissociation channel of water in the evolution of dioxygen in astrophysical applications". Physical Chemistry Chemical Physics 23, n. 15 (2021): 9235–48. http://dx.doi.org/10.1039/d1cp00565k.

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Abstract (sommario):

A recent experiment at the Dalian Coherent Light Source (DCLS) has provided measurements of the partial cross sections for the photodissociation of water vapor over an unprecedented range of wavelengths in the vacuum ultraviolet (VUV) region.

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44

Stutzki, Jürgen. "Observations of CII, CI and CO in Interface Regions". Symposium - International Astronomical Union 150 (1992): 303–8. http://dx.doi.org/10.1017/s0074180900090215.

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Abstract (sommario):

UV-radiation longward of the Lyman edge (912 Å) can escape from HII-regions. It photodissociates carbon monoxide (λ < 1118 Å) and photoionizes neutral atomic carbon (λ < 1101 Å). The resulting CII/CI/CO transition zone on the edges of molecular clouds (photodissociation region or photodominated region: PDR) has been studied in great detail theoretically (Tielens & Hollenbach, 1985; van Dishoek & Black, 1988; Sternberg & Dalgarno, 1989) and these investigations have recently been extended to cover a wide range of densities and UV-intensities (Burton, Hollenbach & Tielens, 1990; Hollenbach, Takahashi & Tielens, 1991; see also A. Sternberg, this volume).

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45

Yin, Tonghui, Liying Ma, Hong Gao e Min Cheng. "Systematical study on photodissociation dynamics of BrCN from 225 nm to 260 nm". Chinese Journal of Chemical Physics 35, n. 1 (febbraio 2022): 86–94. http://dx.doi.org/10.1063/1674-0068/cjcp2111235.

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Abstract (sommario):

The photodissociation dynamics of Br − C bond cleavage for BrCN in the wavelength region from 225 nm to 260 nm has been studied by our homebuilt time-slice velocity-map imaging setup. The images for both of the ground state Br(2P3/2) and spin-orbit excited Br*(2P1/2) channels are obtained at several photodissociation wavelengths. From the analysis of the translational energy release spectra, the detailed vibrational and rotational distributions of CN products have been measured for both of the Br and Br* channels. It is found that the internal excitation of the CN products for the Br* channel is colder than that for the Br channel. The most populated vibrational levels of the CN products are v=0 and 1 for the Br and Br* channels, respectively. For the Br channel, the photodissociation dynamics at longer wavelengths are found to be different from those at shorter wavelengths, as revealed by their dramatically different vibrational and rotational excitations of the CN products.

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46

Chen, Yinjuan, Jiaye Jin, Ke Xin, Wenjie Yu, Xiaopeng Xing, Xuefeng Wang e Guanjun Wang. "Infrared photodissociation spectroscopic studies of ScO(H2O)n=1–3Ar+ cluster cations: solvation induced reaction of ScO+ and water". Physical Chemistry Chemical Physics 21, n. 28 (2019): 15639–46. http://dx.doi.org/10.1039/c9cp02171j.

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Abstract (sommario):

We investigate the gaseous ScO(H₂O)_1–3Ar⁺ cations prepared by laser vaporization coupled with supersonic molecular beam using infrared photodissociation spectroscopy in the O–H stretching region.

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47

Jiang, Pan, Xiaoping Chi, Wenke Qi, Qihe Zhu, Min Cheng e Hong Gao. "Rotational dependence of the branching ratios and fragment angular distributions for the photodissociation of 12C16O in the Rydberg 4p(2) and 5p(0) complex region (92.84–93.37 nm)". Physical Chemistry Chemical Physics 21, n. 26 (2019): 14376–86. http://dx.doi.org/10.1039/c8cp07620k.

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48

Bublitz, J., J. H. Kastner, P. Hily-Blant, T. Forveille, M. Santander-García, J. Alcolea e V. Bujarrabal. "Sampling molecular gas in the Helix planetary nebula: Variation in HNC/HCN with UV flux". Astronomy & Astrophysics 659 (marzo 2022): A197. http://dx.doi.org/10.1051/0004-6361/202141778.

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Abstract (sommario):

Context. Observations of molecular clouds, prestellar cores, and protoplanetary disks have established that the HNC/HCN ratio may be a potent diagnostic of molecular gas physical conditions. The processes that govern the relative abundances of these molecules nevertheless remain poorly understood. Aims. We seek to exploit the wide range of UV irradiation strengths within the ∼pc diameter Helix planetary nebula to explore the potential role of UV radiation in driving HNC/HCN. Methods. We performed IRAM 30 m and APEX 12 m radio line observations across six positions within the Helix Nebula, making use of radiative transfer and photodissociation modeling codes to interpret the results for line intensities and line ratios in terms of the molecular gas properties. Results. We have obtained the first detections of the plasma-embedded Helix molecular knots (globules) in HCN, HNC, HCO+, and other trace molecules. Analysis of the HNC/HCN integrated line intensity ratio reveals an increase with radial distance from the Helix central star. In the context of molecular line ratios of other planetary nebulae from the literature, the HNC/HCN ratio appears to be anticorrelated with UV emission over four orders of magnitude in incident flux. Models of the photodissociation regions within the Helix using the RADEX and Meudon codes reveal strong constraints on the column density (1.5–2.5 × 1012 cm−2) of the molecular gas, as well as pressure and temperature. Analysis of the molecular ion HCO+ across the Helix indicates that X-ray irradiation is likely driving HCO+ production in the outer regions of planetary nebulae, where photodissociation is limited but cold gas and ionized molecules are abundant. Conclusions. Although the observational results clearly indicate that UV irradiation is important in determining the HNC/HCN ratio, our photodissociation region modeling indicates that the UV flux gradient alone cannot reproduce the observed variation in HNC/HCN across the Helix Nebula. Instead, HNC/HCN appears to be dependent on both UV irradiation and gas pressure and density.

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49

Young Owl, Rolaine C., Margaret M. Meixner, Mark Wolfire, A. G. G. M. Tielens e Jan Tauber. "HCN and HCO+Images of the Orion Bar Photodissociation Region". Astrophysical Journal 540, n. 2 (10 settembre 2000): 886–906. http://dx.doi.org/10.1086/309342.

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50

Hasegawa, Tatsuhiko I., e Sun Kwok. "Molecular Line Emissions from the Photodissociation Region of NGC 7027". Astrophysical Journal 562, n. 2 (dicembre 2001): 824–41. http://dx.doi.org/10.1086/323856.

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