Rotational and vibrational temperatures in a 77 K collisionally cooled cell

Abstract

The rotational and vibrational temperatures of CH 3F and SO 2 in a collisionally cooled cell have been investigated. This cell, which uses liquid nitrogen as the cryogen and has an injector whose temperature can be varied between ∼200 and 1300 K, is a variant of liquid helium based systems which we have previously described. The work reported in this paper shows that the rotational temperature is equal to that of the buffer gas, which in turn is variable from 77 K up to the trapping temperature of the spectroscopically active gas by adjustment of the wall temperature of the cell. The vibrational temperature is determined by the vibrational temperature with which the gas is injected, the number of collisions with the buffer gas, and the vibrational deactivation probability of these collisions. Thus, it is shown that the vibrational and rotational temperatures of spectroscopic samples can be separately adjusted over a wide range of temperature with a very simple experimental device. Applications are discussed.