Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 6 1 2006 10.5194/acpd-6-1275-2006 http://www.atmos-chem-phys-discuss.net/6/1275/2006/ http://www.atmos-chem-phys-discuss.net/6/1275/2006/acpd-6-1275-2006.html http://www.atmos-chem-phys-discuss.net/6/1275/2006/acpd-6-1275-2006.pdf 1275 1299 2006-02-17 The quantitative infrared and NIR spectrum of CH₂I₂ vapor: vibrational assignments and potential for atmospheric monitoring T. J. Johnson T. Masiello S. W. Sharpe Pacific Northwest National Laboratory, Richland, WA 99354, USA Diiodomethane (CH₂I₂) photolysis in the presence of ozone is a suggested precursor to new particle aerosol formation, particularly in coastal areas. As part of the PNNL database of gas-phase infrared spectra, the quantitative absorption spectrum of CH₂I₂ has been acquired at 0.1 cm^−1 resolution. Two strong b₂ symmetry A-type bands at 584 and 1114 cm^−1 are observed, but are not resolved at 760 Torr and appear as B-type. In contrast, the b₁ symmetry C-type bands near 5953, 4426 and 3073 cm^−1 are resolved with rotational structure, including Q-branches with widths ≤1 cm^−1. The quantitative infrared and near-infrared vapor-phase spectra (600–10 000 cm^−1) are reported for the first time and discussed in terms of atmospheric monitoring. FT-Raman spectra and ab initio calculations are used to complete vibrational assignments in the C_2v point group.