TUNABLE DIODE-LASER SPECTROSCOPY OF CH3F IN AN EQUILIBRIUM CELL MAINTAINED AT 7.5-K

We report the infrared measurement of rotational and translational temperatures for CH3F in the gas phase with a rotational temperature of approximately 16 K. This measurement is accomplished by extending the collisional cooling technique originally developed for the microwave spectral region to the infrared. We measured an Rand (J,0) feature centered at approximately 1475 cm(-1) in the nu(5) band of CH3F. The rotational temperature was determined by measuring relative intensities of low-J transitions and comparing these results to those predicted by the rotational partition function. We utilized measurements of the absorption linewidth to calculate a translational temperature of 19 K. (C) 1994 Academic Press, Inc.