Locking of the intrinsic angular momentum in the capture of quadrupole diatoms by ions

Abstract

The capture dynamics of rotationally polarised homonuclear diatoms in low-energy collisions with ions is studied theoretically. The interaction potential includes charge-quadrupole and charge-induced dipole terms. The former, taken in the perturbed rotor approximation, exhibits an R À3 anisotropic dependence and causes an only gradual locking of the intrinsic angular momentum of the diatom to the collision axis. As a result, the capture occurs in a regime of incomplete locking, and the passage over centrifugal barriers is accompanied by considerable gyroscopic effects. The j-specific capture cross-sections for rotationally-aligned diatoms show a marked dependence on the polarisation state which is not described by the conventional adiabatic channel model. The latter, however, provides a fair approximation for the cross-sections of unpolarised diatoms. These features are due to a considerable angle of rotation of the collision axis before the barrier is reached and to a small angle of rotation during the passage across the barrier. The numerically determined, scaled, capture cross-sections are represented by an approximate analytical expression that interpolates between two limiting cases, very small (adiabatic channel model) and very large (fly-wheel model) gyroscopic effects of the rotating diatom.

Relocking of intrinsic angular momenta in collisions of diatoms with ions: Capture of H2(j = 0,1) by H2+

“…(2.2) by averaging H over the angle of proper rotation of the diatom in a state with fixed j. 1,2 Then, H PRCl depends on the conjugate dynamical variables (R, P R ) and (ϕ, p ϕ ) where ϕ denotes the precession angle of the vector j about the collision axis and p ϕ is the projection of j onto the collision axis. In addition, H PRCl depends parametrically on the total and intrinsic angular momenta J and j.…”

Electronic nonadiabatic effects in low temperature radical-radical reactions. I. C(3P) + OH(2Π)

“…32 and Eqs. (18) and (19) from Ref. 57) are determined by the asymptotic radial behavior of the valence 2p (q = 1) and inner 2s (q = 3) atomic orbitals of C(2s 2 2p 2 , 3 P) and the valence 1π (q = 2) and upper inner 3σ (q = 4) molecular orbitals of OH(3σ 2 1π 3 , 2 ) (the molecular orbitals being approximated by atomic 2p-orbitals centered at the center-ofmass of OH close to the nucleus of O).…”

“…[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. For example, one determines numbers of open channels W(E,l) (i.e., numbers of ACs for which E > E 0,i (l)) or activated complex partition functions Q * defined by…”

“…14 On the other hand, quantum models are required for ultralow temperature applications. [15][16][17][18] One should note that the AC concept can be exploited in a variety of ways. Besides capture rate constants also capture cross sections in scattering theory have been expressed in terms of numbers of open ACs, see, e.g., Refs.…”

Quantum effects in the capture of charged particles by dipolar polarizable symmetric top molecules. II. Interplay between electrostatic and gyroscopic interactions

“…An extension of this treatment to very low collision energies, where a small number of partial waves contribute to the capture, was done for anisotropic charge-induced dipole interaction, 5 resonance dipole-dipole interaction, 6,7 and charge-quadrupole interaction. 8 In all these cases, the energy-dependent capture rate coefficient approaches a constant value at zero-energy, i.e., it conforms with the Bethe law. 9 For an ion and a dipolar molecule possessing a nonzero average dipole moment in a given rotational state, the first-order charge-dipole interaction falls off as the centrifugal interaction.…”