Theoretical and Experimental Study of the Rovibrational Spectrum of He2-CO

We report calculated microwave and infrared ro-vibrational transitions of the van der Waals complex He-2-CO. The calculations were done using a product basis and a Lanczos eigensolver, together with He-CO and He-He potential functions taken from the literature. The results are found to be in good agreement with previously reported experimental results, and they enable the experimental assignments to be clarified, augmented, and (in one case) corrected. Unlike some other van der Waals complexes with two He atoms such as He-2-N2O, it is not possible to associate a set of energy levels with the torsional motion of the two He atoms oil a ring encircling the dopant (in this case CO). Although we assume that the dipole moment is along the CO axis we find nonetheless that many transitions have appreciable intensity due to ro-vibrational coupling.