Mikhail L. Strekalov

Temperature dependence of the rotational relaxation time in nitrogen

Abstract An electron-beam fluorescence method has been used to study the temperature dependence of the rotational relaxation time characterizing the R-T energy transfer resulting from the free jet expansion of nitrogen for temperatures in the range 6–320 K. Theoretical values calculated in a semiclassical approximation are in good agreement with the present experimental data. The parameters of the anisotropic part of both the repulsive and attractive parts of the interaction potential have been determined earlier through a fitting procedure using the results of other experiments.

Evaluation of the contribution of elastic dephasing processes in linewidths

Abstract The contribution of elastic collisions in vibration–rotation linewidths of diatomic molecules is evaluated in the sudden collision approximation. The developed formalism is used to test the fitting and scaling laws for inelastic rates by experimental linewidths of infrared absorption and Raman spectra.

Temperature dependence of the rotational relaxation cross-section in carbon monoxide

This Letter presents an investigation into the temperature dependence of the relaxation cross-section of the mean rotational energy, σrot, in carbon monoxide. Our data obtained in a free jet at 20–200 K together with high-temperature measurements made by other authors point to non-monotonic behavior of the rotational relaxation cross-section as a function of temperature. A theoretical explanation for such a behavior of σrot with temperature is offered.

Rotational relaxation and collisional energy transfer: Calculations based on a new fitting law

The relaxation of some initially excited molecules (rigid rotators) interacting with a heat bath of other molecules is investigated. We propose a new fitting law for quantitative estimates of the rotationally inelastic rate constants, which is analytically derived from the energy corrected sudden (ECS) approximation. The quasiclassical ECS-E model is shown to give analytical expressions for energy transfer moments, Q-branch line widths and rotational relaxation time. As an example, all higher-order approximations for the rotational relaxation time are obtained in an explicit form. The validity of this model is tested for the case of energy relaxation in nitrogen.

Transition probabilities from highly excited states of anharmonic oscillators under the effect of three-dimensional collisions

Abstract The closed form solution for Morse oscillator transition probabilities valid for highly excited states has been obtained. As an example, we have considered large Δn transitions in vibrationally inelastic scattering of I 2 molecules from two isotopic targets H 2 and D 2 .

Rotational relaxation rates in CO-He mixtures

The rotational level populations of CO molecules were measured in CO(<10%) + He free jets by electron beam fluorescence (in a stationary jet) and resonantly enhanced multiphoton ionization (in a pulsed jet). The measured evolution of the non-equilibrium rotational energy was used to derive the rotational relaxation cross-sections in the temperature range from 6 K to 140 K. To compare and analyse on a common basis all available experimental data (ours and others) on rotational relaxation of CO in He, the infinite order sudden approximation was explored. The following quantities were investigated: integral rotationally inelastic cross-sections, state-to-state rate coefficients, rotational relaxation times, line broadening coefficients, and non-equilibrium rotational energy distributions in a free jet.

Temperature dependence of rotationally inelastic rate constants and fitting laws

The recently developed quasiclassical ECS-E fitting law has been employed to study the temperature dependence of rotational energy relaxation rates. By comparing the rotational energy relaxation cross-sections given by the phenomenological and microscopic approaches, we have derived the relationship between the intermolecular potential parameters and three independent parameters of the model, thus deriving the temperature-dependent form of the quasiclassical ECS-E law. The ability of our model to predict the temperature dependence of the energy relaxation cross-section and the widths of the Raman Q-branch isolated lines has been tested with nitrogen as an example. The method for the determination of anisotropy parameters of the potential (in the form of a non-spherical Morse potential) has been suggested, on the condition that numerical values of the model parameters are determined through an inversion-fitting procedure from the Q(j)-line-broadening coefficients. The primary advantage of our approach is t...

Collisional energy transfer with statistical energy exchange: an analytical solution in the statistical limit

Collisional energy transfer between highly vibrationally excited molecules and bath gas is considered with a statistical kernel, describing energy exchange in complex-forming collisions. Knowledge of the bilinear formula for the Laguerre polynomials offers a means for determining eigenvalues and eigenfunctions of the kernel. An exact solution to master equation for the conditional probability is given as an expansion in terms of these eigenfunctions. The bulk averages of internal energy moments and energy transfer moments are calculated analytically.

Laguerre polynomial solutions to master equation for vibrational energy relaxation in gases

Collisional energy transfer between highly vibrationally excited molecules and a bath gas is considered as a stochastic process occurring in energy space. An exact solution to master equation for the conditional probability is given in terms of simple analytical formulas for weak and strong collisions. The strong collisions are shown to manifest themselves in the distribution pattern composed of maxima and minima in the energy dependence of conditional probability. This effect is explained in detail on physical grounds.

Dynamically based fitting law for cross-sections of vibrational energy transfer

A three-dimensional semiclassical analytical model for cross-sections of vibrational energy transfer in collisions between an atom and a diatomic molecule has been developed. The model is based on the Bessel uniform approximation for transition probabilities valid for highly excited states of a molecule represented by the Morse oscillator. Three fitting parameters of the model are expressed in terms of the features characterizing the anisotropic intermolecular potential. The accuracy and validity of this law are tested by comparison with large Δn transitions and isotope effects in the crossed beam inelastic scattering of I2 from He, H2 and D2.