Relative rate constants for removal of vibrationally excited OH(X 2 π i ) v =9 by some small molecules at room temperature

Vibrationally excited OH in v = 9 [designated OH † (9)] was generated by the reaction of hydrogen atoms with ozone in a fast‐flow discharge system at 300 ± 3 K and a total pressure of 1.1 ± 0.1 torr, with argon as the carrier gas. The addition of a species X, which can deactivate the OH † (9) or react with it, led to a decrease in the Meinel band chemiluminescent emission intensities at both 626 nm (9 → 3 band) and 519 nm (9 → 2 band), which were monitored as a function of the concentration of X. Application of the kinetic scheme developed previously for this chemical system gave the relative rate constant for the removal of OH † (9) by X. The relative rate constants determined in this study, taking O 2 as the reference deactivator ( k   O   2= 1.0), are as follows: He ≤ 0.02; H 2 ≤ 0.05; SF 6 0.09 ± 0.01; CF 4 0.19 ± 0.01; N 2 O 3.5 ± 0.4; NO 17.7 ± 1.5; H 2 O 74.3 ± 2.9; D 2 O 57.6 ± 2.0; NH 3 61.3 ± 1.9; ND 3 58.7 ± 1.6; SO 2 7.1 ± 1.4; COS 8.4 ± 1.7; H 2 S 33.7 ± 8.4; CH 4 1.56 ± 0.03; CD 4 1.06 ± 0.06. Application of these relative rate constants to conditions in the upper atmosphere (60–100 km) suggests that OH † (9) is removed primarily by deactivation by O 2 , and at altitudes ≳90 km, possibly by O( 3 P ). However, since O 2 is unusually efficient for a homonuclear diatomic in deactivating OH † (9), it may not be the primary deactivator for the lower ( v ≤ 8) vibrational levels. These results are compared to earlier studies of OH † (9), and possible mechanisms of interaction of OH † (9) with these molecules are discussed.