New analysis of the 2 ν4, ν4+ ν6, 2 ν6, ν3+ ν4, ν3+ ν6, ν1, ν5, ν2+ ν4, 2 ν3, ν2+ ν6 and ν2+ ν3 bands of formaldehyde H 212C 16O: Line positions and intensities in the 3.5 μm spectral region

Abstract

This work is mainly motivated by the atmospheric importance of formaldehyde. The 3.5 μm region is indeed commonly used for the infrared detection of this molecule in the troposphere and the line parameters which are presently available in the atmospheric databases for H 2CO are of rather poor quality in this spectral range. Using New Fourier transform spectra recorded in LPMA and in GSMA it has been possible to perform an extensive study of the 2ν 4, ν 4+ν 6, 2ν 6, ν 3+ν 4, ν 3+ν 6, ν 1, ν 5, ν 2+ν 4, 2ν 3, ν 2+ν 6 and ν 2+ν 3 bands of formaldehyde. Combining these data with previous frequency and intensity measurements for the ν 3+ν 4, ν 3+ν 6, ν 1, ν 5, ν 2+ν 4, 2ν 3 and ν 2+ν 6 bands [L.R. Brown R.H. Toth and A.S. Pine J. Mol. Spectosc. 406–428 and references therein] and an adequate theoretical model, it proved possible to reproduce rather satisfactorily the experimental data and to generate a list of line positions and intensities for the 3.5 μm region. The Hamiltonian model accounts for the various Coriolis-type resonances and anharmonic resonances which perturb the energy levels of the 4 2, 4 16 1, 6 2, 3 14 1, 3 16 1, 1 1, 5 1, 2 14 1, 3 2, 2 16 1, and 2 13 1 vibrational states. This is also the case for the line intensity calculations, which allow one to reproduce satisfactorily the line-by-line intensity measurements as well as the integrated intensities available in the literature.