The role of vibrational excitation of molecular ions in collisions with neutrals

Transport and dynamic properties of O2+(X2Πg) in Kr under the action of an electrostatic field: single or multiple potential energy surface treatment

Ion transport and dynamic properties are calculated through molecular dynamics simulation of the motion of O(2)(+) in Kr under the action of an electrostatic field. The two lower potential energy surfaces X̃(2)A(") and Ã(2)A(') are considered for the interaction of the Π ground state of the ion with a closed shell noble gas. First, we study the reproduction of experimental mobility data through the use of single and multiple potential energy surfaces and establish the contribution of both lower energy states to the interactions. Further, we obtain mean energies and components of the diffusion coefficient parallel and perpendicular to the field, the latter through calculation of the velocity correlation functions. We also calculate components of the angular momentum which provide a measure of the collisional rotational alignment of the ions at high field strength.

Mixed quantum-classical molecular dynamics simulation of vibrational relaxation of ions in an electrostatic field

The vibrational relaxation of ions in low-density gases under the action of an electrostatic field is reproduced through a molecular dynamics simulation method. The vibration is treated though quantum mechanics and the remaining degrees of freedom are considered classical. The procedure is tested through comparison against analytic results for a two-dimensional quantum model and by studying energy exchange during binary ion-atom collisions. Finally, the method has been applied successfully to the calculation of the mobility and the vibrational relaxation rate of O2+ in Kr as a function of the mean collision energy using a model interaction potential that reproduces the potential minimum of a previously known ab initio potential surface. The calculation of the steady mean vibrational motion of the ions in (flow) drift tubes seems straightforward, though at the expense of large amounts of computer time.