Theoretical and experimental studies of the isotope effects for He-CO and Ne-CO complexes.

In this work, we have studied the isotope effects for the He-CO and Ne-CO complexes by means of theoretical calculations and experimental measurements, which were carried out using a distributed quantum cascade laser to probe a pulsed supersonic jet expansion. Firstly, infrared spectra have been recorded for the He/Ne-CO complexes. Spectroscopic parameters including band origin ν, rotational constants A, B, C, and centrifugal distortion constants Δ were obtained by fitting a Watson A-reduced Hamiltonian with 13 assigned rovibrational transitions for He-CO. For Ne-CO, the observed spectrum produces a set of spectroscopic parameters including the band origin, rotational constants and all the quartic centrifugal distortion constants with more than 100 rovibrational transitions (40 new transitions). Secondly, we have calculated the rovibrational energy levels, vibrational shifts, and rotational constants for the He/Ne-CO complexes based on potential energy surfaces (PESs) and bound state calculations for ground and vibrationally excited states. The obtained results show that the spectroscopic characteristics (vibrational shifts and rotational constants) for Ne-CO are analogous to those of Ar-CO, while those for He-CO show some differences especially for the rotational constants. Finally, according to the available experimental data and our theoretical calculations, infrared spectra were predicted for six isotopologues with C symmetry of Ne-CO complex.