Infrared spectra of the Kr-CO and Xe-CO van der Waals complexes

The infrared spectra of the weakly bound complexes Kr-CO and Xe-CO have bee n studied in the region of the CO stretching vibration (4.7 mu m) using a h igh-resolution tuneable diode laser probe. The complexes were observed in a long path (200 m) low temperature (76 K) gas cell (Kr-CO) and in a pulsed supersonic jet expansion (Kr-CO and Xe-CO). Previous long path cell measure ments on these complexes at lower resolution analysed only the K = 0 and 1 stacks of rotational levels in the ground intermolecular vibrational state. The new data extend up to K = 3 (Xe-CO) or 4 (Kr-CO), and also include K = 0 and 1 stacks in the excited bending state, nu(2) = 1. The bending freque ncies for Kr-CO and Xe-CO (in the nu(CO) = 1 upper state) were determined t o be 13.156 cm(-1) and 13.794 cm(-1), respectively. Detailed molecular para meters were determined to describe the rotational energy levels of each com plex using a simple empirical Hamiltonian. These results enable parameters to be compared for the entire series of rare gas-carbon monoxide complexes, from He-CO to Xe-CO. Also they will guide the future development and evalu ation of accurate intermolecular potential energy surfaces for Kr-CO and Xe -CO.