The weakly bound complex NH₃-CO: Observation and analysis of spectra in the infrared (C-O stretching) and millimetre wave (76–106 GHz) regions

Abstract

The van der Waals complex NH₃-CO has been studied in the infrared and millimetre wave regions, and analysed on the basis of the distinction between the ortho- and para- NH₃-CO nuclear spin species. The spectrum and energy level pattern of ortho-NH₃-CO are relatively simple, closely resembling those of the Ne-CO and Ar-CO complexes. The situation for para-NH₃-CO is somewhat more complicated, with observed states having K values which differ by ±1 from that of the analogous orthoNH₃-CO state. This indicates that the lowest energy orientation of para-NH₃-CO in the complex lies in a II configuration. The present results correlate very well with the only previous study of NH₃-CO, in the microwave region, and clarify the nature of the rotational series observed there. The infrared band centre of NH₃-CO is only very slightly shifted (<0.2cm⁻¹) from that of the free CO molecule, indicating that the CO vibration has little effect on the intermolecular forces.