COLLISION DYNAMICS OF OH(X2-PI, V=9)

Collisional removal rate constants for the OH(X2PI, v = 9) radical are measured for the colliders O2, CO2, and N2O and upper limits are established for He, H-2, Ar, and N2. OH(v = 6) molecules, generated in a microwave discharge flow cell by the reaction of hydrogen atoms with ozone, are excited to v = 9 by the output of a pulsed infrared laser via direct vibrational overtone excitation. The temporal evolution of the v = 9 population is probed as a function of the collider gas partial pressure by a time-delayed pulsed ultraviolet laser. The probe laser light is resonant with the B2SIGMA+-X2PI (0,9) transition and the resulting visible B2SIGMA+-A2SIGMA+ fluorescence is detected with a filtered photomultiplier tube. We measure rate constants for N2O: (6.4 +/- 1.0) x 10(-11) ; CO2: (5.7 +/- 0.6) x 10(-11); O2: (1.7 +/- 1.1) x 10(-11); H-2: < 3 x 10(-12): He: < 2 x 10(-12); N2: < 5 x 10(-13); Ar: < 2 x 10(-13) (all in units of cm3 s-1). For O2 and CO2 these rate constants are significantly faster than those for low vibrational levels and comparable to those for v = 12.