Investigation of Transient Dispersion and Absorption Phenomena with a Bridge Type Superheterodyne Microwave Spectrometer

Abstract

A bridge type superhet spectrometer for time resolved investigation of rotational relaxation is described. Allowing the application of both Stark- and pump-modulation techniques the arrangement may be used for single and double resonance experiments, showing a lot of advantages compared with a conventional Stark- or double resonance-spectrometer. These features are discussed in detail. By means of a MW-pulse method the following two-level experiments have been carried out. The rotational relaxation time T2 was measured by detection of M-unresolved transient emission signals for J = 1 - 2 of 16O12C32S, 16O12C34S and 16O13C32S in natural isotopic abundance and for eight transitions of SO2 up to J = 43. The signals of transient dispersion were detected and compared with those of transient absorption. Their theoretical description in terms of the two-level Bloch equations is discussed.