COLLISIONAL REMOVAL OF O-2(C (1)SIGMA(-)(U), NU=9) BY O-2, N-2, AND HE

The collisional removal of O-2 molecules in selected vibrational level s of the c(1) Sigma(u)(-) state is studied using a two-laser double-re sonance technique. The output of the first laser excites the O-2 to nu = 9 or 10 of the c(1) Sigma(u)(-) state, and the ultraviolet output o f the second laser monitors specific rovibrational levels via resonanc e-enhanced ionization. The temporal evolution of the c(1) Sigma(u)(-) state vibrational level is observed by scanning the time delay between the two pulsed lasers. Collisional removal rate constants for c(1) Si gma(u)(-) nu = 9 colliding with O-2, N-2, and He are (5.2 +/- 0.6) x 1 0(-12), (3.2 +/- 0.4) x 10(-12), and (7.5 +/- 0.9) x 10(-12) cm(3) s(- 1), respectively. As the rate constants for O-2 and N-2 are similar in magnitude, N-2 collisions dominate the removal rate in the earth's at mosphere. For nu = 10 colliding with O-2, we find a removal rate const ant that is 2-5 times that for nu = 9 and that single quantum collisio n cascade is an important pathway for removal. (C) 1996 American Insti tute of Physics.