Jet-cooled and room temperature FTIR spectra of the dimer of formic acid in the gas phase

Room temperature absorption spectra of the gaseous (C-2h) dimer of formic acid were recorded from the lowest energy fundamental, v(16), with origin at 69.2 cm(-1), up to the CH overtone bands with Deltav = 4, with origin at 11,103 cm(-1), using a high resolution Fourier transform interferometer. These spectra are complemented with liquid phase data in the NIR region. In addition, jet-cooled spectra were recorded over the range 1850-3750 cm(-1). The origin of the many observed bands is listed, together with relative intensities for those recorded under jet-cooled conditions. Systematic problems encountered with vibrational assignments for bands other than fundamentals are highlighted and, as a rule, left unsolved except for the bands at 167.26 and 2586.34 cm(-1) tentatively assigned to v(15) + v(16) - v(16) and v(5) + v(22) or v(6) + v(21), respectively. For the first, FIR band the assignment is supported by partly unravelling the hot band pattern around v(15) at 168.47 cm(-1). The jet-cooled rotational contour of the second, MIR band was simulated, allowing the rotational temperature in the jet to be estimated to 35 K. (C) 2004 Elsevier B.V. All rights reserved.