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

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 ≤1 cm−1. The quantitative infrared and near-infrared vapor-phase spectra (600– 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 C2v point group.