Hydrogen bonding in the vapour phase: an unusual type of infrared band

Abstract

Abstract Association bands, due to vibrations of the hydrogen halides modified by hydrogen bonding, have been measured in the near infrared spectra of mixtures of alkyl cyanides with hydrogen chloride or deuterium chloride in the vapour phase. The vibration frequencies of the hydrogen bonds have been estimated. The association band found with mixtures of methyl cyanide and hydrogen chloride, or deutero derivatives of each of these molecules, shows a broad contour upon which a number of sharp peaks are superposed at the lower frequency side. These peaks have been interpreted as being due to an agglomeration of P lines near the band head in each of a series of hot bands which accompany the association band, and which arise from transitions from higher levels of a bending mode of low frequency. The latter appears to have a frequency in the range 20 to 60 cm-1. The spectral analysis suggests that the excitation of the hydrogen halide stretching vibration leads to a shortening of the hydrogen bond.