Absolute Line Intensities and Accurate Line Broadening Parameters for the 5.7µm and 3.6µm Bands of Formaldehyde

The goal of this study was to achieve absolute line intensities and reliable line broadening parameters for the strong 5.7 µm and 3.6 µm bands of formaldehyde (H2CO) and to generate, for both spectral regions, a complete linelist for atmospheric applications. Indeed in common access spectroscopic databases there exists, up to now, no line parameters for the 5.7 µm region (the _2 band), while, at 3.6 µm (_1 and _5 bands together with nine dark bands), the quality of the line parameters is quite unsatisfactory. High-resolution Fourier transform spectra were recorded at LADIR for the whole 1600 _ 3200 cm_1 spectral range and for different path-length-pressure products conditions. Using these spectra, a large set of H2CO individual line intensities and of self- and N2- broadening linewidths were measured. For the line widths of the _2 transitions at 5.7 µm, Complex Robert Bonamy (CRB) calculations were performed, and the calculations and measurements were compared. The experimental intensities were least squared fitted, leading to a set of high quality intensities parameters for both spectral regions. Finally, a linelist was generated in the 5.7 and 3.6 µm regions, and for this task we used the line positions generated previously for the 5.7 µm 1 and 3.6 µm 2 regions. The calculated band intensities derived for the 5.7 µm and 3.6 µm bands are in excellent agreement with the values achieved recently by medium resolution band intensity measurements. It has to be mentioned that intensities in the 3.6 µm achieved in this work are, on the average, about 28 % stronger than those quoted in the HITRAN database. Also at 3.6 µm the quality of the individual line parameters are significantly improved as compared to our previous study performed in 2006b .