Preliminary analysis of CH3D from 3250 to 3700 cm−1

The infrared spectrum of CH3D from 3250 to 3700 cm−1 was studied for the first time to assign transitions involving the ν2 + ν3, ν2 + ν5, ν2 + ν6, ν3 + 2ν6 and 3ν6 vibrational states. Line positions and intensities were measured at 0.011 cm−1 resolution using Fourier transform spectra recorded at Kitt Peak with isotopically enriched samples. Some 2852 line positions (involving over 900 upper state levels) and 874 line intensities were reproduced with RMS values of 0.0009 cm−1 and 4.6%, respectively. The strongest bands were found to be ν2 + ν3 at 3499.7 cm−1 and ν2 + ν6 at 3342.5 cm−1 with integrated strengths, respectively, of 8.17 × 10−20 and 2.44 × 10−20 (cm−1/molecule · cm−2) at 296 K (for 100% CH3D). The effective Hamiltonian was expressed in terms of irreducible tensor operators and adapted to symmetric top molecules. Its present configuration in the MIRS package permitted simultaneous consideration of the four lowest polyads of CH3D: the Ground State (G.S.), the Triad from 6.3 to 9.5 μm, the Nonad from 3.1 to 4.8 μm and now the Enneadecad (19 bands) from 2.2 to 3.1 μm. The CH3D line parameters for this interval were calculated to create a new database for the 3 μm region.