Raman study of Fermi resonance, hydrogen bonding, and molecular reorientation in liquid ammonia

Abstract

The Fermi resonance between the ν₁ and 2ν₄ bands in the polarized Raman spectrum of liquid ammonia was studied as a function of temperature. The resonance interaction was quantitatively analyzed at all temperatures through utilization of the coupled damped oscillator model. The results of this analysis furnish convincing evidence for reversal of the assignment of these bands from that most commonly assumed in the past. An analysis of the temperature dependence of the parameters obtained from the coupled oscillator model (linewidths, uncoupled peak frequencies, and the resonance interaction constant) showed all the results to be self‐consistent and in agreement with the behavior which has been found in other strongly hydrogen‐bonded systems. The polarized and depolarized linewidths of other bands in the spectrum were examined, and they, too, were found to be consistent, given the strong hydrogen bonding in liquid ammonia.