Vibrational Excitation Of Diatomic Molecules Research Articles

The quantum dynamics of the reactions N+H2(HD,D2) and their vibrational excitation effect

The N(4S)+H2 reaction and its isotopic variants have been investigated by means of time-dependent quantum wave packet with split operator method on the ground state potential energy surface (Zhai and Han, J. Chem. Phys. 2011, 135, 104314). The reaction probabilities, integral cross sections, branching ratio of the integral cross sections, and effect of vibrational excitation of H2, HD, and D2 diatomic molecules are presented and discussed. The results reveal that the intramolecular isotopic effect is greater than the intermolecular one, and that the vibrational excitation of the diatomic molecules can promote the progress of this reaction. In addition, a limited number of rigorous Coriolis coupling calculations of the integral cross sections of the N(4S)+H2 reaction have been carried out. Also shown is that since the Coriolis coupling plays a small part in this accurate quantum calculation, the cheaper centrifugal sudden calculations here reported are effective for this reactive system. © 2014 Wiley Periodicals, Inc.

Invariance of quantum optimal control fields to experimental parameters

We consider an ensemble of closed finite-level systems described by a density matrix where the goal is to find an optimal control field to maximize the expectation value of an observable. The eigenvalues of the initial density matrix are assumed to depend on an experimental parameter (e.g., the temperature), whereas the eigenvalues of the observable may depend on an additional application-specific experimental parameter. We show that an optimal control will remain optimal for all such experimental parameters, if the relative ordering, by magnitude, of the eigenvalues of the initial density matrix as well as of the observable is unaltered regardless of the parameter values. More generally, we show like invariance of a control associated with any particular critical point on the corresponding control landscape. The invariance of control laser fields with respect to temperature is illustrated for vibrational excitation of diatomic molecules and photoassociation of atoms.

Ab initio study of the resonant electron attachment to the F2 molecule

Dissociative attachment to and vibrational excitation of diatomic molecules by electron impact is discussed within the projection operator approach. The present method lifts the assumption of separability of the discrete-continuum coupling term Vdε(R), i.e., it is no longer required to write it as a product of a function depending on coordinate R and energy ε separately. The method is applied to the Σu2 resonant dissociative electron attachment to and vibrational electron excitation of the F2 molecule. The required ab initio data have been computed using a recently developed algorithm. This algorithm is based on the Feshbach–Fano partitioning technique and the R-matrix method (FFR). The FFR method is discussed in the context of this particular application.

State-selective vibrational excitation of diatomic molecules coupled to a quasiresonant environment: Markov approximation and non-Markov approach

State-selective vibrational excitation of diatomic molecules coupled to a quasiresonant environment: Markov approximation and non-Markov approach

Estimation of the effect of vibrational excitation of diatomic molecules on their diffusional transport and dissociation in a boundary layer

Relations for the diffusion fluxes of vibrationally highly excited diatomic molecules are found by means of the Chapman-Enskog method. On the basis of these relations a quantitative estimate of the changes in the diffusion coefficients under vibrational excitation and the corresponding changes in the macroscopic dissociation rate is obtained under conditions of disequilibrium of the upper vibrational levels of the dissociating molecules caused by the diffusion processes. The diffusion relations obtained are used in deriving the boundary conditions for the equations of level vibrational kinetics. A simplified version of this derivation is presented for noncatalytic and catalytic surfaces.

Anisotropy and angular dependence of vibrational excitation in ion-molecule collisions: Application to He+ + N2, CO (50 < E < 1000eV)

The dependence of the v=0 to 1 vibrational excitation of diatomic molecules in their ground state by ion projectiles as a function of scattering angle is described using a potential model represented by multipolar and exponential interactions and assuming pure electronically elastic scattering. The linearly forced harmonic oscillator model is assumed in the calculation of the corresponding vibrational energy transfer. This treatment lends itself to solutions in closed analytical form and enables one to investigate the dependence of the vibrational energy transfer upon the molecule orientation. It is applied to He+ + N2 and CO collisions; overall agreement with experiment is found whenever electronic transition processes may be neglected.

Vibrational excitation of diatomic molecules interacting with metal surfaces: heating vs. cooling

Vibrational excitation of diatomic molecules interacting with metal surfaces is investigated theoretically. Vibrational cooling of nitric oxide molecules in trapping-desorption process is explained satisfactorily by the simple calculation based on the kinetic theory of gas molecule-surface scattering and detailed balance relation. Vibrationally assisted sticking and vibrational heating of hydrogen molecules in associative desorption are explained by the coupled channel calculation based on the concept of a reaction path. It is suggested that the occurrence of vibrational heating (vibrational cooling) in desorption may be coordinated generally with the occurrence of vibrationally assisted (vibrationally hindered) sticking.

Charge Transfer and Vibrational Excitation in Molecule-Surface Collisions: Trajectorized Quantum Theory

Vibrational excitation of diatomic molecules scattered from solid surfaces is considered. Emphasis is placed on a mechanism in which charge transfer between the molecule and surface creates a temporary molecular ion. A classical mechanics analysis of this effect has been presented previously. Here a mixed picture is offered in which the center-of-mass translational motion is treated classically with a trajectory approximation (TA) and the intramolecular vibrational motion quantum mechanically. A procedure for insuring energy conservation and microscopic reversibility in the TA is given. Both state-to-state T → V probabilities and mean energy transfer to the vibrational system are calculated for parameters which model N2 and I2 molecules and the results are considered in the light of the "exact" classical mechanics results.

Energy distributions of electronically excited molecules produced by ion bombardment of silicon

We report optical measurements of the internal and kinetic energies of the electronically excited molecules SiN( B 2 Σ) and SiH( A 2 Δ) produced by ion bombardment of silicon. Both molecules are observed to have Boltzmann-like vibrational and rotational energy distributions with average internal energies ~ 0.3 eV, and average kinetic energies ~ 3.0 eV. A simple classical model of vibrational excitation of diatomic molecules due to direct collisional ejection is presented. The model calculations are in qualitative agreement with experimental results, and they illustrate the role of an important dynamical factor — the ratio of the collision duration to the vibrational period of the molecule. There is a propensity for the molecule to respond to collisions as a single unit when this ratio is large, whereas impulsive momentum transfer to the constituent atoms is obtained when this ratio is small.

Nonresonant vibrational excitation of diatomic molecules. Laser-driven Morse oscillator model

Etude pour une molecule heteronucleaire diatomique representee par un oscillateur de Morse charge: pour des frequences du laser superieures a la frequence de vibration de l'oscillateur, les parametres moleculaires dependent parametriquement du champ laser (diminution de l'energie de dissociation et de la frequence de vibration)

The vibrational excitation of diatomic molecules by electron impact

The vibrational excitation of diatomic molecules by electron impact

The vibrational excitation of diatomic molecules by electron impact

The program DSC computes differential cross sections for the electron-impact electronic excitation of diatomic molecules from the corresponding fixed-nuclei T matrices. The momentum-transfer formalism is used to derive a convenient expression of the differential cross section.

Vibrational excitation of diatomic molecules during resonance scattering of slow electrons

An analytic expression is obtained for the process cross section. A Morse oscillator is selected as internuclear interaction potential. The dependence of Γ, the decay width of a compound system, on the internuclear spacing is taken into account. Results of a computation for the molecule N2 are in good agreement with experiment.

Role of the Born-Oppenheimer approximation in the vibrational excitation of molecules by electrons

The role of the Born-Oppenheimer approximation in the resonant vibrational excitation of diatomic molecules by electrons is reexamined in the light of a recent paper on the hybrid theory and calculation of $e+{\mathrm{N}}_{2}$ scattering by Chandra and Temkin. It is pointed out that it is not necessary to resort to a nonadiabatic vibrational close-coupling expansion to reproduce the substructure seen in the resonant vibrational excitation cross section of ${\mathrm{N}}_{2}$ by electrons. Finally, comment is made on the reasons for the slow convergence of the vibrational close-coupling treatment from a compound-state point of view of the scattering process.

Impulse approximation for three-dimensional inelastic atom—diatomic-molecule collisions

The impulse approximation of Chew is applied to the calculation of the cross sections for rotational and vibrational excitation of diatomic molecules by collisions with an atom. The assumptions underlying the impulse approximation are discussed and found to be justified for these processes. A closure approximation is used to perform the sums over rotational quantum numbers in the expression for the vibrational-excitation cross section and the resulting expression depends on two factors; an oscillator form factor and the scattering amplitudes for atom-atom scattering. Vibrational-transition probabilities, evaluated for oxygen-carbon monoxide collisions assuming that the oscillator is harmonic and using a rough estimate for the typical atom-atom scattering amplitudes, are in qualitative agreement with experiment. Further refinements and extensions of the model are discussed.

Application of the Adiabatic-Nuclei Theory to Vibrational Excitation

The adiabatic-nuclei theory is shown to be quantitatively applicable to vibrational excitation of diatomic molecules by electron impact. When the dependence of the fixed-nuclei phase shifts on internuclear separation is approximated by a two-term Taylor series, the resulting formulas are transparent and easily evaluated. Application to e-H2 excitation is made, phase-shift derivatives are estimated, and the theory is found to fit experimental data.

A model potential for vibrational excitation of diatomic molecules

A model interaction potential for the vibrational excitation of H 2 by Li + of the form C exp(−α x +β y ) is studied using non-iterative integral techniques. The results show that vibrational excitation is sensitive to small quantitative change in qualitatively similar surfaces.

Post-Threshold Energy Dependence of the Cross Section for Endoergic Processes: Vibrational Excitation and Reactive Scattering

The essential features of the translational energy dependence or excitation function σ(Etr) for two types of endoergic collisional processes are deduced on the basis of information on the inverse, exoergic processes. Microreversibility is conveniently exploited via the symmetric yield function, Y(E), which is uniquely determined at a given total energy, E. In the case of the vibrational excitation of diatomic molecules by atomic or molecular impact (T → V), use is made of the abundant data on the temperature dependence of the V → T relaxation time τ. The usual semiempirical two-parameter representation of the relaxation process is transformed to yield an explicit functionality for the translational energy dependence of the inelastic excitation cross section σ0 → 1 (Etr), in the adiabatic region. For diatomics whose relaxation is slow (e.g., slow enough to be studied in a shock tube) the vibrational excitation cross section σ0 → 1 is exponentially small in the post-threshold region. These systems would be unsuitable for study by the crossed beam technique; the latter thus complements rather than replaces the more traditional relaxation methods. Also considered are endoergic chemical reactions whose inverse processes involve negligible activation barriers (e.g., ion—molecule reactions, reactive atom—molecule reactions, etc.). In all cases the dominant post-threshold energy dependence of the reactive cross section σR(Etr) for the endoergic process is fixed via the microreversibility constraint, so experimental data in this region do not provide as much information as is available from studies of the exoergic process. The deviation from a simple Arrhenius cross section functionality is determined by the long-range final product interaction.

Application of the Adiabatic-Nuclei Theory to Vibrational Excitation

The adiabatic-nuclei theory is shown to be quantitatively applicable to vibrational excitation of diatomic molecules by electron impact. When the dependence of the fixed-nuclei phase shifts on internuclear separation is approximated by a two-term Taylor series, the resulting formulas are transparent and easily evaluated. Application to $e\ensuremath{-}{\mathrm{H}}_{2}$ excitation is made, phase-shift derivatives are estimated, and the theory is found to fit experimental data.

Qualitative interpretation of resonance effects in vibrational excitation cross sections of diatomic molecules by slow electrons

It is suggested to solve the problem of resonance vibrational excitation of diatomic molecules colliding with slow electrons without using a formal expansion in wave functions with complex eigenvalues. The main point is to overcome the difficulties associated with the necessity of considering at the same time a large number of inelastic channels so as to account for the long range part of the interaction potential. In the model proposed inelastic scattering is determined by the parameters of a single interaction potential, determining also elastic scattering. As a result we obtain as a special case an equation similar in structure to that of Herzenberg and Mandl [1] for evaluating cross sections. As an example numerical calculations were performed for spherical square well potentials, indicating the presence of characteristic resonance cross sections already in this simplest case.