Collision-induced dissociation dynamics in O2++Ne(Ar) collisions: The role of electronic excitation

Abstract

Integral collision-induced dissociation (CID) cross sections at center-of-mass (CM) energies ranging from threshold to 22 eV and product ion recoil velocity distributions are presented for O2++Ne(Ar) collisions. The O2+ ions are produced in an electron impact ion source and thus have ∼0.5 eV of vibrational energy. The O2++Ne CID cross sections are observed at energies below the 0 K thermodynamic threshold of 6.66 eV, implying the possibility of significant vibrational effects. A second CID threshold is apparent at 9±1 eV. This is close to the charge-transfer (CT) threshold energy. No CT products are observed. The O2++Ar CID cross section rises rapidly above a relative translational energy onset of 7.5±0.2 eV and reaches a maximum value of ∼0.8 Å2 at 14 eV (CM). A CT onset of 6.0±0.2 eV is observed which is close to the thermodynamic threshold for CID. The energy dependence of the CT cross section is very similar to the CID cross section except for a small step at energies where CID becomes efficient. The CID recoil velocity distributions near threshold are centered at the CM velocity and shift to forward preference at higher energies. The O2++Ar CT recoil velocities are forward scattered near threshold and become centered with respect to the CM velocity at energies where competition with CID is apparent.