Microwave spectroscopy of nonlinear free radicals - I. General theory and application to the Zeeman effect in HCO

Abstract

A general theory for the description of the microwave spectra of nonlinear open-shell molecules in the presence of external electric or magnetic fields is presented using irreducible tensor methods. This theory provides the basis for discussion of the possible detection of electric dipole transitions between states of a nonlinear free radical. Detection of the four components of a K -doubling transition in small magnetic fields for the free radical HCO between 8.3 and 8.7 GHz is described and the spectrum is analysed in terms of the theory presented earlier. The molecular parameters which result from this analysis are compared with those obtained from solid-state studies.