Recent microwave studies of internal rotation and molecular structure

Abstract

The microwave spectra of several molecules with a sixfold barrier are described. These barriers are expected to be low but the practical method of spectroscopic analysis depends on the reduced barrier height. Molecules with a light internal top such as CH 3NO 2 and CH 3BF 2 are treated in the free-rotor limit. On this basis the spectrum of CH 3BCl 2, a new microwave molecule, has been analysed; the structure and 35Cl quadrupole coupling constants are reported. Molecules possessing a heavy internal symmetric top such as SiF 3BF 2, CF 3NO 2, (CH 3) 3CNO 2 and (CH 3) 3CBF 2 exhibit microwave spectra of intermediate barrier type. Recent barrier and structural results are discussed.