The effect of dynamics on band shapes of hydrogen bonded complexes in solution

We study the IR absorption of the νs (XH) mode of a hydrogen bonded species (XH---Y) in solution. Our theory assumes that the dephasing of the νs dipole transition is due to coupling to the low frequency stochastic νσ (XH---Y) stretching mode. Our approach is novel in that it uses Kubo’s stochastic Liouville equation to include both dynamics and Fermi resonance coupling of the νs levels with other intramolecular levels. Spectra assuming three bath models (Smoluchowski, Ornstein–Uhlenbeck, and Zwanzig) are compared and discussed. The theory gives good overall qualitative agreement with experiments involving moderate strength hydrogen bonds. It also demonstrates that the overall shape of the band can be analyzed in terms of parameters that affect primarily νs, and that dynamics should be included for a realistic description of these bands.