PHOTOFRAGMENTATION INFRARED-EMISSION STUDIES OF VIBRATIONALLY EXCITED FREE-RADICALS CH3 AND CH2L

Time and wavelength-resolved infrared fluorescence techniques are used to study the photofragmentation dynamics of CH2I2 and CH 3I at the excimer laser wavelengths of 248 and 308 nm. Emission is detected from vibrationally excited CH2I and CH3 radicals as well as from the excited iodine atoms [I*(2P 1/2→2P3/2)] produced in the photolysis. A complete infrared fluorescence spectrum of the highly excited CH2I radical is obtained as a function of time after the 248 nm dissociating laser pulse, providing both spectroscopic and vibrational deactivation data for the radical. Significant CH2I emission is observed at all wavelengths, indicating that excitation occurs into a very high density of states, nearing the vibrational quasicontinuum. Stronger emission features are observed in the region of the C-H stretching vibrations, the CH2 bending motion, and a combination band of these two modes. Deactivation rates for various spectral features of the highly excited CH2I radical with CH2I 2 and argon are presented, along with a discussion concerning the relaxation of the highly excited radical spectrum. In the photolysis of CH 3I at 248 nm, infrared fluorescence is observed directly from the out-of-plane bend of the CH3 radical. In addition, at 248 nm, the quantum yield (Φ1*) for I*(2P 1/2) production is measured to be 0.81±0.03 for CH 3I and 0.46±0.04 for CH2I2, while dissociation of CH2I2 at 308 nm yields Φ1* = 0.25±0.02. The I* quenching rates with CH3I and CH2I2 are measured to be (2.5±0.4)10-13 and (3.6±0.3)10-13 cm 3 molecule-1 sec-1, respectively. © 1980 American Institute of Physics.