The quantitative infrared and NIR spectrum of CH₂I₂ vapor: vibrational assignments and potential for atmospheric monitoring

• Main Authors: T. J. Johnson, T. Masiello, S. W. Sharpe
• Format: Article
• Language: English
• Published: Copernicus Publications 2006-01-01
• Series: Atmospheric Chemistry and Physics
• Online Access: http://www.atmos-chem-phys.net/6/2581/2006/acp-6-2581-2006.pdf
• ISSN: 1680-7316; 1680-7324

Diiodomethane (CH₂I₂) has recently become a molecule of significant atmospheric interest as it can contribute to coastal IO formation. 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 when broadened to 760 Torr with nitrogen 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 &le;1 cm^-1. The quantitative infrared and near-infrared vapor-phase spectra (600&ndash;10 000 cm^-1) are reported for the first time. Some bands are discussed in terms of their potential for atmospheric monitoring and theoretical detection limits on a selected basis. FT-Raman spectra and ab initio calculations are used to complete vibrational assignments in the C_2<i>v</i> point group.