VIBRATIONAL RELAXATION TIMES FROM INFRARED EMISSION INTENSITIES

Abstract

Two general processes can contribute to the rate of change of population of a molecular energy level in a gaseous sample. These are (a) emission or absorption of radiation, and (b) collisional excitation or de-excitation. A simple steady state treatment gives the intensity of emission, which is proportional to an excited state population, in terms of the rate constants for processes (a) and (b). The two processes have different dependences on pressure, (a) being first order and (b) second order; thus measurement of intensity of emission as a function of pressure allows a comparison of the rate constants of (a) and (b). Since the emission and absorption constants may be found from absolute absorption intensity measurements, it should be possible to determine vibrational relaxation times by this method. Some experimental results obtained on gases heated to $2-300^{\circ} K$ at pressures down to a few tenths of a millimeter will be presented and experimental difficulties discussed.