Collision-induced dissociation dynamics in O-2(+)+Ne(Ar) collisions: The role of electronic excitation

Integral collision-induced dissociation (CID) cross sections at center-of-m ass (CM) energies ranging from threshold to 22 eV and product ion recoil ve locity distributions are presented for O-2(+)+Ne(Ar) collisions. The O-2(+) ions are produced in an electron impact ion source and thus have similar t o0.5 eV of vibrational energy. The O-2(+)+Ne CID cross sections are observe d at energies below the 0 K thermodynamic threshold of 6.66 eV, implying th e 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 O-2(+)+Ar CID cross section rises rapidly above a relative translational energy onset of 7.5 +/-0.2 eV and r eaches a maximum value of similar to0.8 Angstrom (2) at 14 eV (CM). A CT on set of 6.0 +/-0.2 eV is observed which is close to the thermodynamic thresh old 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 beco mes efficient. The CID recoil velocity distributions near threshold are cen tered at the CM velocity and shift to forward preference at higher energies . The O-2(+)+Ar CT recoil velocities are forward scattered near threshold a nd become centered with respect to the CM velocity at energies where compet ition with CID is apparent. (C) 2000 American Institute of Physics. [S0021- 9606(00)00243-9].