New high-resolution analysis of the ν7and ν9 fundamental bands of trans-formic acid by Fourier transform infrared and millimeter-wave spectroscopy

The high-resolution (0.002 cm(-1)) spectrum of the v(7) (OCO scissor mode) and v(9) (COH torsion mode) fundamental bands of trans-formic acid (HCOOH) at 15.8 mum was recorded by Fourier transform infrared spectroscopy. In addition, millimeter-wave transitions within the 7(1) and 9(1) vibrational states were measured in the spectral range 340-600 GHz. Using these new experimental data, an extensive analysis of the nu(7) and nu(9) bands was performed. The model we have used accounts for the strong A- and B-type Coriolis interactions which couple the 7(1) and 9(1) vibrational states and which were already pointed out in the literature [J. C. Deroche, J. Kauppinen and E. Kyro. J. Mol, Spectrosc. 78, 379-394 (1979); E. Willemot. J. Mol. Spectrosc. 120, 246-275 (1986)]. The observed levels are fit to within the experimental accuracy leading to the determination of a precise set of band centers of nu(7) and nu(9) at 686.1656 cm(-1) and 640.7251 cm(-1), respectively, and rotational and Coriolis constants. (C) 2002 Elsevier Science (USA).