Fourier transform microwave spectra of the very weakly bound He–CO2 dimer

Abstract

Spectra of pure rotational transitions of the very weakly bound He–CO2 van der Waals complex were investigated using a pulsed molecular beam Fourier Transform microwave spectrometer. The complex exhibits very large amplitude internal vibrational motions and the rotational transitions were, as a consequence, difficult to locate and to assign. Eight isotopomers, namely He–CO2, He–13CO2, He–OC18O, He–O13C18O, He–18OC18O, He–18O13C18O, He–OC17O, and He–O13C17O, were studied in order to establish the assignments. The hyperfine structures due to the quadrupolar 17O nucleus were resolved and analyzed in the two 17O containing isotopomers. The observed nuclear quadrupole hyperfine structures not only provide further confirmation for the assignment but also give new information about the angular anisotropy of the He–CO2 interaction potential.