Overtone spectroscopy of formic acid

Vibrational assignments of fundamental, combination and overtone bands in the main isotopomer of gaseous transformic acid are reported from spectra either newly or previously [J. Chem. Phys. 113 (2000) 1535] recorded using high-resolution Fourier transform and intracavity laser absorption spectroscopies. A total of 62 bands, with 32 newly reported ones, are observed from the lowest energy band, nu(7) at 626.16 cm(-1) up to 4nu(1) at 13284.1 cm(-1). Among these bands, 43 are firmly assigned, and 16 tentatively. Effective vibrational constants are obtained. The normal modes of vibrations are further characterised using ab initio calculations providing fundamental band intensities and picturing normal mode nuclear displacements. The effective investigation of the rotational structure in the first CH stretch overtone band (2nu(2)) and in the second OH stretch overtone band (3nu(1)) is detailed. Rotational information is also presented for 3nu(2) and two close-lying bands, that could be extracted from the strong overlapping formic acid dimer bands using artificial filtering procedures. (C) 2002 Elsevier Science B.V. All rights reserved.