Temperature-dependent infrared spectra of torsional vibrations in acetic acid

The mid-IR and near-IR vapor phase spectrum of CH3COOH was examined with a focus on the regions of the ν17 O-H torsion and the ν1 O-H stretch. Each region showed a number of peaks that were assigned using previous ab initio work, their temperature dependence, and analysis of the deuterated species of acetic acid (CD3COOH, CH3COOD, and CD3COOD). These assignments correct and improve upon the values currently used in the literature. Many of the peaks were assigned as hot bands associated with either the ν17 O-H torsion or the ν1 O-H stretch. In addition, the first definitive assignment of the Q-branch of the ν1 O-H stretch was made. The hot bands were shown to contribute a significant amount of absorption intensity to the ν1 region at 298 K. An empirical temperature-dependent correction to the total absorption of the ν1 O-H stretching region as well as an adjusted absolute cross-section for ν1 are given and suggested for future use.