The Infrared Spectrum and the Structure of Gaseous Nitrous Acid

An investigation of the infrared spectrum of nitrous acid has shown that in the gaseous state this substance exists in two tautomeric species which are believed to be trans- and cis-forms. The cis-form is of higher energy by about 506 calories mole–1. A complete vibrational analysis is given and the OH in plane bending frequencies are found to be 1260 cm–1 and ~1292 cm–1, and the out of plane frequencies 543 cm–1 and 637 cm–1 for the trans- and cis-molecules, respectively. From the rotational constants the O[Single Bond]N[Single Bond]O angle is estimated to be 118° for the trans-form and 114° for the cis-form, from which conclusions are drawn regarding the electronic structure of the molecule. The standard entropy of nitrous acid at 25° is calculated