Translational and Internal State Distributions of NO Produced in the 193 nm Explosive Vaporization of Cryogenic NO Films: Rotationally Cold Translationally Fast NO Molecules.

摘要

The translational, rotational, and spin-orbit state distributions are reported for fast NO molecules which are generated by the 193 nm laser vaporization of 30 K multilayer NO films. Rotational distributions in nu=0 are obtained by laser multiphoton ionization for five different velocities ranging from 900 to 2200 m/s, corresponding to translational energies E sub t = 0.14 to 0.71 eV. In every case, the average molecular rotational energy is more than 10 times smaller than the component of translational energy normal to the surface. Average rotational energies (E sub R) range from 0.009 + or - 0.002 to 0.024 + or - 0.006 eV (with corresponding best fit temperatures, T sub Rot = 105 to 220 K). For the molecules with E sub t 0.14 and 0.22 eV, the spin-orbit population ratios are typically comparable with T sub Rot and increase to a value F2/F1 of 1.1 + .05 or - .04 (statistical ratio) for NO molecules with E sub T = 0.71 eV. In some cases, the rotational distributions have a non-Boltzmann, high J component. Preliminary investigations for molecules with E sub T = 0.56 eV indicate that the vibrational distribution nu = 1/nu=0 is 3 + or - 1% (T about T 785 K). The rotations in nu = 1 are also cold ((Er about 0.01 eV, T sub rot about 130 K). The mechanisms that causes the ejection of translationally fast, rotationally cold NO molecules is considered in terms of either a collisional cooling process following desorption or rotationally constrained desorption dynamics. Reprints. (jhd)