Applications of pulsed microwave-microwave double resonance: I. Relaxation studies in gases

Abstract

The time-resolved response of a gas absorber exposed to two independent sources of microwave radiation, one steady and the other pulsed, is described using a formalism based on the Bloch equations for a three-level system. This predicts that a series of experiments can be made on the resonant and off-resonant recoveries of the absorptive and dispersive properties of a single sample by which the individual collisional relaxation parameters that characterise its rotational states may be separately measured. Some of these can be determined only by double-resonance experiments. The construction and operation of amicrowave double-resonance bridge spectrometer capable of carrying out these experiments is described, and results obtained for the (J=2 from 1)-(J=1 from 0) system of OCS are discussed in detail. The polarisation relaxation rate for the 2 from 1 transition is found to be 38.2(2) mu s-1 Torr-1 and its population relaxation rate, including cross-relaxation effects, is found to be 38.9(1.9) mu s-1 Torr-2. Values for the cross-relaxation parameters are obtained for the first time.