Near-infrared spectroscopy of H 3 O + ⋯X n (X = Ar, N 2 , and CO, n = 1-3).

Near-infrared (NIR) spectra of H 3 O + ⋯X n (X = Ar, N 2 , and CO, n = 1-3) in the first overtone region of OH-stretching vibrations (4800-7000 cm -1 ) were measured. Not only OH-stretching overtones but also several combination bands are major features in this region, and assignments of these observed bands are not obvious at a glance. High-precision anharmonic vibrational simulations based on the discrete variable representation approach were performed. The simulated spectra show good agreement with the observed ones and provide firm assignments of the observed bands, except in the case of X = CO, in which higher order vibrational mode couplings seem significant. This agreement demonstrates that the present system can be a benchmark for high precision anharmonic vibrational computations of NIR spectra. Band broadening in the observed spectra becomes remarkable with an increase of the interaction with the solvent molecule (X). The origin of the band broadening is explored by rare gas tagging experiments and anharmonic vibrational simulations of hot bands.