Parameters of pulsed supersonic jets of SF 6 and NH 3 molecules studied using a spectrometer with tunable diode lasers

Abstract

A qualitative pattern of cooling molecules in a pulsed supersonic jet is given on the basis of literature data. A procedure of measurements is described and known relations are presented which allow the determination of rotational temperatures and concentrations of molecules in a jet using the measured intensities of infrared absorption lines. The parameters of SF<SUB>6</SUB> and NH<SUB>3</SUB> jets have been determined for various pulsed valves by means of tunable diode lasers. We used pulsed supersonic jets to study collisionless infrared excitation of SF<SUB>6</SUB> and NH<SUB>3</SUB> molecules by an intensive laser field. An important point in the treatment of these experiments was to know with sufficient accuracy the concentration of molecules in a jet and their distribution over rotational levels of the ground vibrational state (characterized by the rotational temperature T<SUB>rot</SUB> in the case of Boltzman distribution). We determined these parameters from the measurements made by means of tunable diode lasers. Various pulsed valves were tried which allowed us to obtain jets with different gas temperatures and different concentrations of molecules.