THE ROTATIONAL SPECTRUM OF CIS- AND TRANS-FORMIC ACID, REVISITED

Abstract

The initial experimental confirmation of the existence of the cis rotamer of formic acid, HCOOH, was based on a small number of pure rotational transitions in the microwave region [W. H. Hocking, Z Naturforsch. 31a, 1113-1121 (1976)]. Since then, there have been no further report of the observation of spectral features attributable to this species. In order to extend the study of the spectrum of cis-HCOOH we have recorded the far infrared spectrum of HCOOH from 30 to $100 cm^{-1}$ (Oberpfaffenhofen). This spectrum has now been supplemented by millimeter wave measurements (Kharkov) and submillimeter wave measurements (K\""oln), so that a very extensive set of data is now available for both rotamers. The analysis of the spectrum (Giessen, Kharkov)has now yielded a more complete set of ground state constants for each rotamer than was previously available, providing in particular a sound basis for the search for infrared transitions of cis-HCOOH.