We report two complementary experimental investigations of the absorption spectrum of molecular oxygen between 243 and 258 nm. In the first experiment, excitation of O2 is inferred by detecting oxygen atoms resulting from chemical reaction. In the second experiment, absorption by O2 is observed directly by cavity ring-down spectroscopy. Absorption strengths for the Herzberg I [Formula: see text], Herzberg II [Formula: see text], and Herzberg III [Formula: see text] band systems are modeled with the DIATOM spectral simulation computer program using the best available branch intensity formulas. Absolute oscillator strengths are derived for all three systems and compared with values in the literature.

OH collisional removal rate constants for υ=8, 10, and 11 with O2, N2, CO2, N2O, and He are measured. Vibrationally excited OH molecules in υ=5, 7, and 8 are prepared from the reaction of atomic hydrogen with ozone, and selectively excited to υ=8, 10, and 11, respectively, with a pulsed infrared laser via direct overtone excitation. Subsequent collisional deactivation of these laser-populated levels is probed as a function of collider gas partial pressure using a time-delayed, pulsed ultraviolet laser resonant with OH(B 2Σ+−X 2Π) transitions. Fluorescence from OH(B 2Σ+−A 2Σ+) is detected. These results complete a series of removal rate constant measurements for OH(X 2Π) up to υ=12. Resonance enhancement effects in vibration-to-vibration energy transfer for CO2 and N2O factor significantly in the vibrational-level-dependent rate constants.

Laser double resonance study of collisional removal of O2(A 3Σ u +,υ=7) with O2 J. Chem. Phys. 100, 744 (1994); 10.1063/1.466943 Collisional transitions obeying nondipolar selection rules between M levels of FCN, a lasermicrowave doubleresonance study Appl. Phys. Lett. 31, 268 (1977); 10.1063/1.89656Double resonance study of collisional relaxation on the frequency coincidence between the ν2 R (2,0) line of 15NH3 and the R (42) line of CO2 laserThe collisional removal of O 2 molecules prepared in selected vibrational levels of the A 3~: state is studied using a two-laser double-resonance technique. The output of the first laser excites the O 2 to A 3~:, v=6, 7, or 9, and the ultraviolet output of the second laser monitors these levels via resonance-enhanced ionization through either the v=5 level of the C 3IIg Rydberg state, or the valence state or states tentatively associated with the 5 3IIg state. The temporal evolution of the A 3'k: state vibrational level is observed by scanning the time delay between the two pulsed lasers. Collisional removal rate constants are obtained for A 3'k:, v=7 and 9 colliding with O 2 , N 2 , CO 2 , Ar, and He; and for v=6 colliding with O 2 and N 2 . We find the collisional removal of the A 3~: state to be fast (k;;:.10 -11 cm 3 s -1) for all colliders studied. The rate constants vary by about an order of magnitude from the fastest collisional deactivator, CO 2 to the slowest studied, the rare gases Ar and He. The rate constants for the atmospherically important colliders O 2 and N2 are similar in magnitude and suggest that N z collisions will dominate the removal rate in the Earth's atmosphere.

Collisional removal rate constants for the OH (X 2Π,ν=7) radical are measured for the colliders O2, CO2, and N2O, and an upper limit is established for N2. OH(ν=4) molecules, generated in a microwave discharge flow cell by the reaction of hydrogen atoms with ozone, are excited to ν=7 by the output of a pulsed infrared laser via direct vibrational overtone excitation. The temporal evolution of the ν=7 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 (0,7) band of the B 2Σ+−X 2Π transition. Fluorescence from the B 2Σ+ state is detected in the visible spectral region. We measure rate constants for CO2, (6.7±1.0)×10−11; N2O, (3.0±0.6)×10−11; O2, (7±2)×10−12; and N2, <6×10−13 (all in units of cm3 s−1).