Spectroscopic study of the v6=1 and v8=1 vibrational states of formic acid, HCOOH:: New assignments of laser transitions

The FTIR spectra of the Coriolis-coupled nu(6) and nu(8) bands of formic acid, HCOOH. were measured with a resolution of ca. 0.003 cm(-1). A total of 4878 and 1203 transitions of the nu(6) and nu(8) bands with J' values up to 70 and 44, respectively, were assigned. A combined fit of the assigned FTIR transitions together with the available microwave, laser-saturated, and newly measured millimeter- and submillimeter-wave transitions made it possible to improve significantly the parameters of these states and to determine for the first time five new coupling parameters. The RMS deviation of the infrared data was 0.00022 cm(-1). Thirteen previously unassigned optically pumped transitions have been identified. (C) 2002 Elsevier Science (USA).