Evolution of the νHF absorption bands of B⋯HF complexes on transition from the gas to liquid phase

Abstract

Abstract FTIR spectra of the νHF bands in B/HF mixtures (B=Xe, CO2, CO, HCN, CH3CN) have been recorded with densities varying from the dilute gas to liquid at room temperature. The vibration–rotational bands of free HF molecules in all systems were calculated for the density ranging from 1 to 400 amagat, and, by separating the bands, the νHF band shape of bound molecules were determined. It was shown that on transition from the gas to liquid phase the νHF band of B ⋯ HF complexes shifts toward low frequencies and symmetrizes. The vibration–rotational νHF band of these complexes in the gas phase was calculated using a model with the anharmonic coupling between νHF and low-frequency vibrational modes. It was established that the model taking into account the spectral exchange applied to a system consisting of rotational and low-frequency vibrational subsystems provides a correct description of evolution of the νHF complex band with increasing density.