Spectroscopic Study of the I2 Formation from the Photolysis of Iodomethanes (CHI3, CH2I2, CH3I, and CH2ICl) at Different Wavelengths

Emission spectra following the photolysis of iodomethanes (CHI3, CH2I2, CH3I, and CH2ICl) at 266 nm were recorded in a slow flow cell. In addition to emission from the electronically excited species including CH (A2Δ, B2Σ–, and C2Σ+), C2 (d3Πg), and atomic iodine (4Po), a series of emission bands was observed in the 12 000–19 000 cm–1 region. The dominant structure of these emission bands was verified as the I2 B3Π+ 0,u–X1Σ+ g emission at the 532 nm excitation, and the observed I2 was formed from collisions between iodine atoms generated from the C–I bond dissociation in these iodomethanes. The I2 emission spectra following the photolysis of CH2I2 at different wavelengths were acquired, and the threshold energy for the first C–I bond cleavage was determined to be 208 ± 1 kJ mol–1. We also obtained the emission spectra of pure I2 at several visible excitation wavelengths for comparison with those from the photolysis of iodomethanes, and a least-squares global fit of the observed I2 emission bands yields more accurate anharmonicity parameters for the vibrational structure in the I2 B–X transition.