Academic literature on the topic 'Quantum States - Diatomic Molecules'

Through continual advancement in laser pulse technology. experimentalists now have al their disposal higher intensities (> 1015 W cm!) and shon.er pulse durations « 10 fs) than ever before. Using sllch technology it is possible to probe and manipulate the electronic and nuclear Illotions in even the smallest fastest-moving diatomic molecules. The first pan. of this thesis presents a simplified theoretical model that allows one to adequately treat the nuclear vibrational and photodissociation dynamics of the O2 ' molecular ion, when subjected to typical infrared wavelengths. Direct comparison between the predictions of this theoretical model and recent experimental observations is provided. The same model is then used as a basis for the proposal of a number of novel techniques that utilize ultrashort laser pulses to l;:ontrol both the dissociation pathway and the population ofthe bound vibrational levels. One of the main areas of theoretical and experimental advancement in recent decades has been the area of cold atom trapping and manipulation. The second part of this thesis considers the theoretical treatment of two interacting particles, confined in various one-dimensioDal potentials. These systems represent a fundamental building block that has been made accessible through recent developments in the field of ultracold atomic physics: The numerical scheme for the treatment of the two-particle system is described and results are presented for two-paJ1icles in a harmonic trap, a o-split harmonic trap. and a double-well potential. Propel1ies of the two-particle ground state and low-energy excited states are examined including the energy spectra, eigenfunctions, reduced single-particle density matrices, momentum distributions and entanglement. ]n particular, focussing upon how these quantities depend upon the two parameters, particle-particle interaction strength and barrier height. In this way, the present work relates to the scope of quantum state control, in such systems, through variation of 'experimentally accessible' control parameters.

The work carried out during this thesis focuses on the quantum dynamics of the diffusion of hydrogen atoms on a surface of palladium (111). The study of the 3D system allowed us to detail the infrared spectrum of H/Pd (111), showing the existence of different adsorption sites on which localized states exist that are strongly coupled (Fermi resonance). This phenomenon governs the diffusion of hydrogen atoms in an ultra-fast time scale (fs).The study of the (6D) H2/Pd(111) system has shown that the transitions observed are in fact transition bands between several quasi-degenerate adsorption states. The agreement between the calculated and measured values is significantly less good than that between the data calculated for the 3D system and the measured data. Does adsorbed hydrogen on palladium exist in the form of a weakly bound H2 molecule? This thesis has provided some answers to this question, which remains open, hovewer, to some extent.

<p>The main theme covered in this thesis is experimentalstudies of quantum dynamics and coherent control in homonuclearalkali diatomic molecules by ultrafast laser spectroscopy iththe implementation of pump-probe techniques.</p><p>A series of experiments have been performed on the Rb2molecules in a molecular beam as well as in a thermal oven. Thereal-time molecular quantum dynamics of the predissociatingelectronically excited D(3)¹Πu state of Rb₂, which couples to/intersects several otherneighbouring states, is investigated using wavepackets. Thepredissociation of the D state, explored by this wavepacketmethod, arises from two independent states, the (4)³Σ_u⁺and (1)³∆_u, for which the second corresponds to a much fasterdecay channel above a sharp energy threshold around 430 nm. Thelifetime of the D state above the energy threshold is obtained,τ ≈ 5 ps, by measuring the decay time of thewavepacket in a thermal oven. Further experimentalinvestigation performed in a molecular beam together withquantum calculations of wavepacket dynamics on the D state haveexplored new probe channels of wavepacket evolution: theD′(3)1Σu+ channel, which exhibits vibrational motionin a shelf state and the (4)³Σu+ channel, where direct build-up of thewavefunction is observed due to its spin-orbit oupling to the Dstate.</p><p>The real-time quantum dynamics of wavepackets confined totwo bound states, A¹Σ_u⁺(0_u⁺) and b³Π_u(0_u⁺), have been studied by experiment andcalculations. It is shown that these two states are fullycoupled by spin-orbit interaction, characterised by itsintermediate strength. The intermediate character of thedynamics is established by complicated wavepacket oscillationatterns and a value of 75 cm^-1is estimated for the coupling strength at thestate crossing.</p><p>The experiments on the Li₂molecule are performed by coherent control ofrovibrational molecular wavepackets. First, the Deutsch-Jozsaalgorithm is experimentally demonstrated for three-qubitfunctions using a pure coherent superposition of Li₂rovibrational eigenstates. The function’scharacter, either constant or balanced, is evaluated by firstimprinting the function, using a phase-tailored femtosecond(fs) pulse, on a coherent superposition of the molecularstates, and then projecting the superposition onto an ionicfinal state using a second fs pulse at a specific delay time.Furthermore, an amplitude-tailored fs pulse is used to exciteselected rovibrational eigenstates and collision induceddephasing of the wavepacket signal, due to Li₂-Ar collisions, is studied experimentally. Theintensities of quantum beats decaying with the delay time aremeasured under various pressures and the collisional crosssections are calculated for each well-defined rovibrationalquantum beat, which set the upper limitsfor ure dephasingcross sections.</p><p><b>Keywords:</b>Ultrafast laser spectroscopy, pump-probetechnique, predissociation, wavepacket, pin-orbit interaction,coherent control, (pure) dephasing</p>

In this work an attempt has been made to develop a computer program package that can be used to simulate/model spectra and other properties of the majority of diatomic molecules. Specifically, the program package aims at: <I>(i)</I> providing a general tool for the interpretation of experimental spectra and for pointing out any perturbation that may exist in them; and <I>(ii)</I> to help researchers in setting up their experiment and know in advance optimum conditions to perform it. The program package under development at present includes the following features: 1. Generation of molecular potentials; 2. Calculation of Frank-Condon factors and transition probabilities; 3. Simulation of spectra in adsorption, emission, laser-induced fluorescence and resonance ionisation; 4. The inclusion of thermal and non-thermal level population distribution; 5. In case of perturbations, the ability to read the energies of the levels as input parameters, rather than calculating them for inadequate formulas based on standard spectroscopic constants. The program package was tested for a few diatomic molecules, selected specifically to be representative for typical cases in laser absorption and emission spectroscopy.

Cette thèse s'articule autour de développements méthodologiques sur l'évaluation théorique des énergies quantiques et relativistes d'état électroniquement excité d'atome ou de molécule. La méthode basée sur la fonction d'onde "Coupled Cluster" (CC) est à l'heure actuelle, une des méthodes les plus précise pour calculer ces états pour les systèmes à N-corps. L'implémentation présentée est basée sur un Hamiltonien relativiste à N-corps: Dirac-Coulomb à 4 composantes et une fonction d'onde "Coupled Cluster" au rang d'excitation arbitraire. Les états excités sont évalués via la théorie de la réponse linéaire, en diagonalisant la matrice Jacobienne Coupled Cluster. L'accent des travaux se porte sur l'évaluation de ses éléments en seconde quantification via un nouvel algorithme basé sur les commutateurs, et sur son adaptation au formalisme relativiste de Dirac à 4 composantes. Enfin, des applications du code à des molécules diatomiques non triviales seront présentées<br>This thesis focuses on methodological developments of the theoretical evaluation of the quantum and relativistic energy of electronically excited states of an atom or a molecule. The wave-function method Coupled Cluster (CC) is currently one of the most accurate methods to calculate these states for many-body systems. The implementation presented is based on the many-body relativistic 4-component Dirac-Coulomb Hamiltonian and a Coupled Cluster wave function at arbitrary excitation rank. The excited states are evaluated using linear response theory by diagonalizing the Coupled Cluster Jacobian matrix. The work focuses on the evaluation of these second-quantized elements using a new commutator-based algorithm, and on its adaptation to a Dirac 4-component relativistic formalism. Finally, I present some applications of the code to challenging diatomic molecules