Direct observation of rotational transitions of the CO–CO dimer

Abstract

Measurements of five pure rotational transitions of a mixed isotopomer of the CO–CO van der Waals dimer with a Fourier transform microwave spectrometer in the frequency range from 3 to 19 GHz are reported. For symmetry reasons, pure rotational transitions in the vibrational ground state are not accessible in the symmetric 12C16O–12C16O species, and the mixed 12C16O–13C16O isotopomer was studied instead. The observed lines were identified as belonging to the 12C16O–13C16O dimer by isotopomeric variation of the sample composition, monitoring of the microwave excitation pulse conditions, and comparison of the measured frequencies with those predicted in a recent infrared study. [M. D. Brookes and A. R. W. McKellar, J. Chem. Phys. (submitted).]