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

We report the translational, rotational, and spinhyphen;orbit state distributions of fast NO molecules which are generated by the 193 nm laser vaporization of 30 K multilayer NO films. Rotational distributions inv=0 are obtained by laser multiphoton ionization for five different velocities ranging from 900 to 2200 mthinsp;sminus;1, corresponding to translational energiesET=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 lang;ERrang; range from 0.009plusmn;0.002 to 0.024plusmn;0.006 eV (with corresponding best fit temperatures,TRot=105 to 220 K). For the molecules withET=0.14 and 0.22 eV, the spinndash;orbit population ratios are typically comparable withTRot. For higher translational energies, the typical spinndash;orbit ratios are larger than expected fromTRotand increase to a valueF2/F1of 1.1plusmn;0.50.4(statistical ratio) for NO molecules withET=0.71 eV. In some cases, the rotational distributions have a nonhyphen;Boltzmann, highJcomponent. Preliminary investigations for molecules withET=0.56 eV indicate that the vibrational distributionv=1/v=0 is 3plusmn;1percnt; (Tape;785 K). The rotations inv=1 are also cold (lang;ERrang;ape;0.01 eV,TRotape;130 K). The mechanism 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.