Kazuhiro Sakimoto

Influence of the Dipole Interaction on the Low-Energy Ion-Molecule Reactions

Collision dynamics of an ion-polar molecule system is influenced considerably by the dipole interaction. The recently-developed PRS (Perturbed Rotational State) approach is applied to the problem. It is found that the ion-polar molecule reaction rate is more than ten times larger in interstellar molecular clouds than the widely-used Langevan value. A scaling law holds approximately for the effective cross section as a function of the collision energy.

Low-Energy Ion-Polar Molecule Collision –Further Study in Perturbed Rotational State Approach–

A good convergency of the semiclassical PRS method, developed recently by K. Takayanagi (J. Phys. Soc. Jpn. 45 (1978) 976, referred to as I), has been confirmed. The straight-line trajectory treatment has proved to be a good approximation for the low-energy ion-polar molecule collision where the long-range dipole interaction is dominant. A scaling low derived in I is found useful for predicting rotational excitation cross sections for a large number of collision pairs.

Rotational Excitation of Symmetric-Top Molecules by Low-Energy Ion Impact

Theory of collisions between ions and symmetric-top molecules is formulated. This work is to investigate the adiabatic nature of low energy ion-polar molecule collisions. When the angular momentum quantum number projected on the symmetry axis of symmetric-top molecules is not zero, the elastic collision is significantly different from that where the molecule is linear, but not so much for the inelastic collision. Some discussions about the scaling law obtained by Takayanagi and about the modified Born approximation are given.

Semiclassical Decoupling Schemes in Molecular Collisions

Several decoupling schemes are discussed for the semiclassical impact parameter treatment of collisions between atoms and linear rigid rotors. First, a decoupling method analogous to the quantum mechanical one originated from the conservation of parity is found also in the semiclassical treatment. Next, presently derived semiclassical versions of l -dominance and decoupled l -dominance approximations provide us with an intuitive understanding of the physical meaning of these approximations. Numerical applications are performed for the H + –CO collision system.