On the meaning of ?Collision Rate Constants? for ion-molecule reactions: Association of hydrogen atoms with C6H5+ and small alkyl radicals with C7H7+ ions

C. J. COBOS; H.-J. TROE; A. I. MAERGOIZ; A. A. VIGGIANO; S. G. ARD; N. S. SHUMAN

INTERNATIONAL JOURNAL OF MASS SPECTROMETRY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2020 vol. 458

1387-3806

Limiting high pressure rate constants for the association of H with C6H5 + and of CH3,C2H5, and n-C3H7 radicals with C7H7 + molecular ions are analyzed in terms of ?rigidity factors? arising from the anisotropy of the interaction potentials and ?collision rate constants? in the absence of anisotropy (the latter corresponding to phase space theory, PST). Model calculations based on ab initio potential energy surfaces show that the PST rate constants k PST(T) exceed collision rate constants fromconventional ion-molecule capture theory (in this case given by Langevin rate constants kL). They can be represented by k PST(T) = kL + kh.sph. where kh.sph. denotes hard-sphere collision numbers with collision radii r0. The r0 derived from the modelled k PST(T) are related to properties of the interaction potentials. Application to other ionmolecule reactions are proposed.