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Processes with Participation of Electronically and Vibrationally Excited Particles with Khimera

Quantitative data on the cross sections and rate constants of the processes of generation and relaxation of electronically and vibrationally excited particles are of great importance for kinetic modeling in materials, environmental chemistry, plasma chemistry and plasma processing.

Universal Set of Processes Accessible for Treatment by Khimera
Photoexcitation of molecules, photodissociation of molecules, predissociation of molecules, quenching of excited atoms, V-T V-R-T V-V energy transfer

The state of art models of generation and relaxation of electronically and vibrationally excited particles incorporated into Khimera are based on the qualitative physical ideas about the character of electronic potential surfaces of the systems and their dynamics. The main simplification of dynamics underlying all the models is the use of a quasiclassical or classical approximation treating the motion of nuclei.


Cross-section of CH molecule photodissociation from the X2Π electronic bound state to the upper 22Σ unbound state is calculated using theab initio potential curves. The Born–Oppenheimer approximation is used for the description of the molecular energy levels.
Example: photodissociation of CH molecule

The cross section of the photodissociation of the CH molecule from the X2Π electronic bound state to the upper 22Σ unbound state is calculated using the corresponding ab initio potential curves. The electronic dipole moment D(R) of the X2Π–22Σ electronic transition as a function of the internuclear distance R is obtained from quantum chemical calculations. The Born–Oppenheimer approximation is used for the description of the molecular energy levels. The results of calculations and a comparison of the results of calculation are shown in the figure.

 


Rate constant of the electronic quenching processes O(1D)+Ar(1S) → O(3P) + Ar(1S) evaluated using Landau-Zener model which allows calculating rate constants of electronic energy transfer induced by nonadiabatic transitions at the crossings of electronic potential curves of diatoms.
Example: electronic deactivation in atomic collisions O(1D) + Ar →O(3P) + Ar

Rate constant of the electronic quenching processes O(1D)+Ar(1S) → O(3P) + Ar(1S) was evaluated using Landau-Zener model incorporated to Khimera. The model allows calculating rate constants of electronic energy transfer induced by nonadiabatic transitions at the crossings of electronic potential curves of diatoms. In the case of the process under consideration there exist three such crossings which contribute to the overall rate constant. The parameters of the O-Ar diatom necessary for the application of the Landau-Zener model were calculated using quantum chemistry. It is seen that Landau-Zener model with the parameters obtained from quantum chemical calculations provides quantitative description of electronic quenching in atomic collision.


Rate constant of the vibrational transition from the first excited vibrational state of N2 to the ground state in collisions with He (N2(v=1)+He → N2(v=0)+He) evaluated in the framework of the Schwartz-Slawsky-Herzfeld (SSH) theory of VT energy exchange in collisions involving diatomic molecules. The parameters of interaction between N2 and He were evaluated ab initio within the framework of DFT using the Gaussian 2003 program package.
Example: vibrational energy transfer in collisions of N2 with He

The rate constant of the vibrational transition from the first excited vibrational state of N2 to the ground state in collisions with He (N2(v=1)+He → N2(v=0)+He) was evaluated in the framework of the Schwartz-Slawsky-Herzfeld (SSH) theory of VT energy exchange in collisions involving diatomic molecules. The parameters of interaction between N2 and He were evaluated ab initio within the framework of DFT using the Gaussian 2003 program package. The results are presented in the picture along with the available experimental data. It is seen from the picture that SSH theory provides a quantitative description of the vibrational relaxation of diatomic molecules.