Collisional relaxation of vibrationally excited O/sub 2//sup +/ ions
Vibrationally excited O/sub 2//sup +/ ions were produced and injected into a helium flow tube and found to survive more than 10/sup 5/ collisions with He atoms without significant relaxation. The first, second, and higher vibrational states of O/sub 2//sup +/ were detected by their enhanced reactions with Xe, SO/sub 2/, and H/sub 2/O. Using these reactions as probes for vibrational excitation, the relaxation of O/sub 2//sup +/ (v = 1) and O/sub 2//sup +/ (v = 2) ions was studied for collisions with Ne, Ar, Kr, H/sub 2/, D/sub 2/, N/sub 2/, CO, CO/sub 2/, H/sub 2/O, CH/sub 4/, SO/sub 2/, SF/sub 6/, and O/sub 2/. The resulting quenching rate constants were found to vary from 1(-9) to <2(-15) cm/sup 3/ s/sup -1/. The quenching rate constant of O/sub 2//sup +/ (v = 2) was approximately twice that of O/sub 2//sup +/ (v = 1) in each case. The rate constants were found to correlate with the bond energy of the ion--molecule collision complex. For CO/sub 2/, Kr, and O/sub 2/, the energy dependence of the quenching rate constant was investigated in the range 0.04--0.3 eV. The results indicate that the relaxation process proceeds through a long-lived complex where the vibrational excitation is transferred into the weak complex bond resulting in dissociation, analogous to vibrational predissociation in van der Waals complexes. In the special case of O/sub 2//sup +/ (v)--O/sub 2/ collisions, the relaxation is clearly dominated by the resonant charge transfer process and the rate constants for v = 1 and v = 2 are found to be equal.
- Research Organization:
- Aeronomy Laboratory, NOAA Environmental Research Laboratories, Boulder, Colorado 80303
- OSTI ID:
- 5636823
- Journal Information:
- J. Chem. Phys.; (United States), Vol. 79:9
- Country of Publication:
- United States
- Language:
- English
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640304* - Atomic
Molecular & Chemical Physics- Collision Phenomena