Measurement of rotational energy transfer rates for HD (v=1) in collisions with thermal HD

Abstract

We report state-to-state rotational energy transfer rates for HD excited to the first excited vibrational level of the ground electronic state. Stimulated Raman scattering is used to produce the rotationally selected, vibrationally excited HD. Subsequent collisional energy transfer from the prepared state, upon collision with a thermal distribution of HD, is monitored by multiphoton ionization through the E,F electronic state. The data are analyzed by solving the rate equations coupling the lowest six rotational states of the first excited vibrational level. In this manner, both the absolute rate constants and the shape of the energy transfer probability density function are determined. The best fit of the data to trial probability density functions indicates that the HD–HD collisions preserve the magnetic sublevel, mj. The total rotational energy transfer rate out of a particular rotational level is compared to high resolution Raman linewidth measurements in order to determine the degree to which the rotational energy transfer rate contributes to the linewidth.