title: [Vibrational to rotational energy transfer between CsH (Chi1 Sigma+, nu > or = 15) and CO2].
abstract: The quenching of highly vibrational excited CsH through collisions with a 500 K bath of CO2 was investigated using the laser spectroscopy technique. CsH was formed by the Cs(7P)+H2 reaction. The pulse laser prepared CsH in the highly vibrational levels. Laser induced fluorescence was used to detect collisionally relaxed CsH. The relaxation rate coefficient of CsH (nu" = 21) with CO2 is 10 times larger than that of CsH(nu" = 15). Relaxation of CsH(nu") with H2 was also investigated. The mass effect on the collisional relaxation rate coefficients is strong. The observed collisional relaxation rate coefficients of H2 are bigger than those of CO2. Energy gain into CO2 resulting from collisions with excited CsH was probed using laser overtone spectroscopy technique. Distributions of nascent CO2 rotational population in the ground (00(0)0) state were determined. For CsH excited at nu" = 15, the scattered CO2 molecules have a rotational temperature of T(rot) = (605 +/- 50) K. For excitation at nu" = 21, the CO2 rotational temperature is T(rot) = (780 +/- 70) K. Based on the rotational temperatures, the average change in the CO2 rotational energy <deltaE(rot)> has a stronger dependence on the CsH initial energy. Using the ambient cell temperature, <deltaE(rot)> nu = 21 -2. 7 <deltaE(rot)> nu" = 15 was found. The nascent distributions of recoil velocities for collisions were determined from stimulated absorption line profiles of individual CO2 rotational states. For nu" = 15, scattered CO2 molecules with J = 36-48 have center of mass translational energy of <E(rel)> = 600-972 cm(-1). For nu" = 21, the values increase to <E(rel)> = 972-1 351 cm(-1). Based on propensity rules for collisions that favor small changes in energy and angular momentum, it is reasonable that low-J CO2 states will have lower translational energy than the high-J states. Extrapolating nu" = 15 and 21 data to the initial relative translational energy of E0 = 520 cm(-1) gives an estimate of the threshold states J(th) = 34 and 24, respectively. The onset of large <E(rel)> is likely to occur at J states that are larger than J(th).
authors: School of Physics, Xinjiang University, Urumqi 830046, China.
authors: Kang
authors: K
authors: Dai
authors: Shu-Ying
authors: SY
authors: Wang
authors: Jing
authors: J
authors: Liu
authors: Yi-Fan
authors: YF
authors: Shen