COLLISION DYNAMICS OF OH(X2-PI-I,V=12)

Collisional removal rate constants for the OH radical in v = 12 of the ground electronic state are measured for the colliders CO2, O 2, N2, H2, He, and Ar. OH molecules, generated in v = by the reaction of hydrogen atoms with ozone, are excited to v = 12 by direct overtone excitation with pulsed infrared laser light. The temporal evolution of the v = 12 radicals is probed as a function of collider gas pressure by a time-delayed pulsed ultraviolet probe laser. The probe laser is used to excite the molecules via the B 2Σ+ -X 2Πi (0,12) electronic transition, and the resulting B 2Σ+ -A2Σ+ fluorescence is detected. We measure rate constants for CO2:(5.6 ± 1.5) × 10-11; O2:(1.6 ± 0.2)×10 -11; He:(3.6±0.6)×10-12; H 2:(3.0±0.8)×10-12; Ar:(2.6±0.5)XlO- 12;N2:(2.5±0.7)×10-12 (all in units of cm3 s-1). These rate constants are over fifty times faster in all cases than the vibrational relaxation rate constants for the lower levels (v = 1 and v = 2) of the ground state. © 1990 American Institute of Physics.