Rotational Energy Transfer in Molecular Collisions and Parameters of Power-Gap "Law"

The quantum mechanical integral inelastic cross-sections for the rotation transitions in a diatomic molecule with an atom were computed and analysed by using the empirical power-gap "law" over a wide range of collision energy. A well-known parameter, |ΔE|$\text{}^{*}$, of the power-gap "law" was estimated by observing a rapid fall of cross-sections for the rotational energy transfer, |ΔE| ≥ |ΔE|$\text{}^{*}$. It was found that |ΔE|$\text{}^{*}$ corresponds to classical limit of maximum amount of rotational energy transfer permissible by the angular momentum conservation constraints and the hard ellipsoid potential model provided the hard ellipsoid potential surface is represented by the classical turning point surface of the real potential employed in the computation of cross-sections. Such an agreement is shown to be useful in the determination of the difference of major and minor axes of the intermolecular-potential ellipsoid from the knowledge of the cross-sections and the power-gap "law"

The Hard Ellipsoid Potential Model for the Rotational Energy Transfer and its Region in Molecular Systems

The hard ellipsoid potential model for understanding the mechanism of the rotational energy transfer in a diatomic molecule due to collisions with an atom was explored by performing quasi-classical trajectory calculations on N$\text{}_{2}$-He and N$\text{}_{2}$- Ne systems governed by a sum of pairwise atom-atom Morse interactions. It is found that the conversion of the orbital angular momentum into the angular momentum of the molecule takes place when the colliding atom is very close to the classical turning point ellipsoid. The quantitative measures to define such closeness were introduced. Further, it is observed that nearly 50% of the total angular momentum transfer takes place when the colliding atom approaches the classical turning point ellipsoid and the remaining 50% transfer takes place while the atom bounces back