Electron diffraction studies of laser‐pumped molecules. IV. SF6, experiment and theory

Abstract

A model of absorption of infrared radiation by supersonic jets proposed in paper III was tested experimentally. New nozzle designs permitted pumping the ν3 mode of SF6 at power densities in excess of 104 W/cm2. Vibrational excitation corresponding to the absorption of up to 3.6 photons/molecule was deduced from the increased amplitudes of vibration of the SF, FFcis, and FFtrans atom pairs and the lengthening of the SF bond. At high excitations, electron diffraction intensities were accounted for best if it was assumed that two subsets of molecules were produced, one much hotter than the other. Vibration–vibration relaxation from ν3 to the other stretching modes was too fast to be followed. Relaxation of stretching to bending could be monitored, crudely, at lower pressures where approximately 30 collisions were needed at the depressed temperatures in the jet. At higher pressures and excitations V‐T/R relaxation was observed, corresponding to a transfer of perhaps one‐tenth of the vibrational excitation in the course of 103 collisions. Excitation as a function of gas density, power density, and nozzle diameter was accounted for satisfactorily by the model of paper III.