On the vibrational relaxation of diatomic molecules at intermediate excitation

The theory of quasistationary vibrational distributions of diatomic molecules at low gas temperatures is developed for the case of intermediate excitation temperatures when the flow of quanta is nondiffusional in Treanor's part of the distribution. In certain conditions the distribution contains a region of inversion which is followed by a plateau.     

Squeezing the ground vibrational state of diatomic molecules

We study the squeezing of minimal width vibrational wave packets of diatomic molecules, like Na₂, by using several laser schemes that couple the ground and excited electronic configurations of the molecule. The different schemes imply diabatic and adiabatic laser transformations, or a combination of both, whose efficiency and required physical resources are compared and analyzed.     

Calculation of vibrational constants of diatomic molecules

We apply Wigner's effective-harmonic-oscillator (EHO) function with the Morse potential to the calculation of vibrational constants of diatomic molecules. A one-particle system is described by the operator representation of Wigner's function. We find the EHO parameters both for a single molecule and for an equilibrium ensemble of molecules. We obtain numerical values of the constants for the iodine molecule.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 485–487, July–August, 1988.     

On irregular oscillatory structures in resonant vibrational excitation cross-sections in diatomic molecules

We examine in detail the origin of irregular oscillatory structures in the cross-sections of low-energy resonant vibrational excitation of several diatomic molecules by electron impact. We show that these irregularities are caused by a combination of two phenomena: enhancing of the magnitude of the nuclear wave function in the vicinity of poles in the complex energy plane corresponding to quasi-bound vibrational states of the molecular anion, and energy variations of the phase of the nuclear wave function which corresponds to the reflection in the potential well of the molecular anion and which are sometimes called boomerang oscillations. These two phenomena are usually both involved in the nuclear dynamics. The former one is usually dominant at lower energies (NO molecule) and in systems where the potential energy of the molecular anion (H₂ in high rotational states) possesses an outer potential well. The latter one dominates if the width of the quasi-bound vibrational states of the molecular anion is relatively large (e.g. at higher energies for NO and N₂ molecule, H₂ in ground state).     

Effects of rotation on vibrational relaxation in diatomic molecules

An approximate method is presented for allowing for the effects of rotation on the rate of vibrational relaxation in a diatomic molecule; this is based on local separation of the variables in the interaction region. An interpretation is given for experiments on the vibrational relaxation of HI in a shock wave.     

A poisson equation for vibrational potentials of diatomic molecules

A Poisson equation for nuclear motions in diatomic molecules is derived. The working formula is whereV _α ² is the Laplacian operator for the position of nucleusα, W is the Born-Oppenheimer molecular energy, is the atomic number ofα, and ? _β (α) is the electronic charge density evaluated atα due to orbitals centered onβ. Harmonic, anharmonic and quartic equilibrium force constants are calculated using Hartree-Fock molecular and atomic electronic charge densities, for a number of first and second row diatomic molecules. A charge-model field gradient formula for harmonic force constants $$k_e = {3 \mathord{\left/ {\vphantom {3 {R_e^3 ,}}} \right. \kern-\nulldelimiterspace} {R_e^3 ,}}$$ wherek _e is the force constant andR _e the equilibrium internuclear distance, which offers general improvement over a similar formula due to Bratoz, is presented.     

A model potential for vibrational excitation of diatomic molecules

A model interaction potential for the vibrational excitation of H₂ by Li⁺ of the form C exp(−αx+βy) is studied using non-iterative integral techniques. The results show that vibrational excitation is sensitive to small quantitative change in qualitatively similar surfaces.     

Simultaneous vibrational relaxation and thermal dissociation of diatomic molecules

A model of a truncated harmonic oscillator with equidistant levels and one-quantum transitions is applied. The balance equations for O₂ have been solved numerically with 26 levels, with the transition probabilities taken as P _k,k +1k exp (k) P ₁₀, in which k is the number of the level and is an adjustable parameter that takes account of the anharmonicity. A Boltzmann distribution is obtained up to level 19 with =0, but for 0 there are deviations from that distribution in lower levels. Levels with k=1, 2, 3 are populated with relaxation times substantially less than the relaxation time for the vibrational energy. Dissociation depletes levels with k 19.     

Relaxation effects accompanying core ionization in diatomic molecules

The influence of electronic relaxation on the bond-length charges following inner-shell ionisation in diatomic molecules is studied. CO and N₂ are treated explicitly. Transition operators are used for predicting renormalized vibrational coupling constants and slopes of relaxation energy surfaces.     

Tunable raman excitation and vibrational relaxation in diatomic molecules

A generalization of the Raman vibrational excitation technique is presented. It is applied here to the room temperature study of V→T transfer in pure N₂ and O₂ or in mixtures with H₂ and He. The results on N₂ are the first obtained at room temperature, those on O₂ are in good agreement with existing data and provide a check of validity of the method.     

Structural dependence of the fragmentation of naphthalenesulfonyl halide and naphthalenesulfonamide molecules under electron ionization

By mass spectrometry it is found that naphthalene, 1-naphthalenesulfonyl chloride, 2-naphthalenesulfonyl fluoride, 2-naphthalenesulfonyl chloride, 1,5-naphthalenedisulfonyl chloride, 1-naphthalenesulfonamide, and 2-naphthalenesulfonamide evaporate congruently on heating and their saturated vapor is presented by the corresponding monomeric molecular forms. The relationship is established between the character of the fragmentation of molecules during electron ionization and the specific features of their geometric and electronic structures.     

Semiclassical three-dimensional model for vibrational energy transfer in diatomic molecules

A semiclassical model for calculation of rate constants for vibrational excitation in diatomic gases at low temperatures (below 1000 K) is suggested. The model has been tested by its ability to predict the relaxation times of hydrogen (τ_H1 in the temperature region 40–1000 K. The agreement with experimental values is excellent. The isotopic ratio τ_D2/τ_H2 as a function of temperature is predicted.     

Accurate electron affinities of several diatomic and triatomic molecules

The electron affinity of several diatomic and triatomic molecules is computed with an error of less than 0.1 eV using the second-order Møller-Plesset method and a 6.311 + G(2d,2p) basis set. The importance of the zero-point energy correction is tested and a comparison with the results obtained with other basis sets is made.     

Threshold peaks in the vibrational excitation of molecules by electron impact: a time-dependent view

Resonance and threshold effects in low-energy electronmolecule collisions are analyzed in a time-dependent picture. Time-dependent wave packets reflecting the non-Markovian open-system dynamics of electron-molecule collision complexes are explicitly generated for two representative models of pures-wave scattering and dipole-modifieds-wave scattering, respectively. The numerical results demonstrate the relevance of the adiabatic potential-energy curves of resonances, virtual states and bound states for a qualitative understanding of the dynamics and lucidly reveal the existence of nonadiabatic processes in such systems.     

Spectroscopic calculations of electron diffraction parameters of diatomic molecules

Using spectroscopic data, the electron diffraction parameters r_g and l_e for the iodine and oxygen molecules are calculated at various temperatures by numerical diagonalization of the vibrational hamiltonian matrix and by the density matrix approach. The results are discussed and compared with available experimental data. A comparison is also made with the results of second-order perturbation calculations for iodine reported in the literature.     

On the preference for vibrational energy in diatomic dissociation

Recent measurements of dissociation and relaxation rates, and of dissociation induction times, are shown to indicate very serious depletion of vibrational state populations during thermal dissociation. The large measured dissociation rates are then only compatible with dissociation from low vibrational states, i.e., there can be at most a very weak bias favoring vibrational excitation in thermal dissociation. It is suggested that dissociation from low vibrational states is assisted by rotational excitation.     

Master equation approach to vibrational energy transfer between two diatomic molecules

In this paper a semiclassical non-markovian master equation is derived. We begin by using the well-known tetradic form of the Liouville equation for a reduced density operator. By projecting the diagonal matrix elements of the operator, we obtain an infinite-order master equation. This equation is then applied in the lowest-order approximation to collinear collisions between the diatomic molecules: H₂H₂, N₂N₂ and Cl₂Cl₂. With an assumed form of the interaction potential for such a problem we have also derived an analytical expression for the V—V transition probabilities. They are then calculated over a wide range of velocities of the colliding molecules and compared with exact semiclassical ones. An excellent agreement of the results is found for small velocities (i.e. υ ≈ 10⁴ cm/s). For larger values of υ (≈ 10⁵ cm/s) the results obtained from the master equation approach agree with the exact ones only in the low-velocity range for light molecules and low oscillatory states.     

The absorption spectrum resonance structure of diatomic molecules near the ionization threshold

The problem of the near-threshold photoionization of the non-symmetrical molecules XY is formulated in connection with the problem of scattering of the emitted electrons by molecular ions using the integral multichannel quantum defect methods and results of the adiabatic approximation. In addition to the general theory, analytical formulae are obtained describing the simplest two-channel cases which demonstrate specific features of interference structure of absorption spectra as well as the role of various factors in the formation of the line profile     

Disparate effects of rotational energy excitation on the electron impact ionization of diatomic molecules: H2 versus N2

Rotational energy excitation produces disparate effects on the ionization efficiency curves of H₂ and N₂. While no observable shift in the N₂ ionization curve occurs on heating, the H₂ ionization curve is displaced significantly, indicating that, in the case of H₂, rotational energy is being efficiently converted into electronic energy.