Computer simulation of the infrared spectrum of hydrogen bonded crystalline formic acid

Abstract

The theory of hydrogen-bond IR spectra in molecule crystals containing four hydrogen bonds in a unit cell is presented in order to explain the interaction mechanism determining the ν OH bandshape in the formic acid crystalline spectrum. On the basis of the vibrational hamiltonian and the vibrational transitional selection rules for the system a computer reconstitution was performed of the bandshape for the HCOOH, DCOOD, HCOOD and DCOOH crystalline spectra, which were otherwise known from the literature. The computed bandshapes and those taken from the literature agreed reasonably. Analysis of the coupling parameters taken for simulation of the spectra leads to the observation of an anomaly in the distortion parameter upon deuteration of formic acid. It is suggested that a resonance interaction between ν OH and ν CH stretching vibrations may be responsible for this.