Spectroscopic Investigation of the Multiphoton Photolysis Reactions of Bromomethanes (CHBr3, CHBr2Cl, CHBrCl2, and CH2Br2) at Near-Ultraviolet Wavelengths

Nascent emission and laser-induced dispersed fluorescence spectra of products or intermediates from the multiphoton photolysis reaction of bromomethanes (CHBr3, CHBr2Cl, CHBrCl2, and CH2Br2) at 266 nm were recorded in a slow flow cell. Electronically excited species including CH (A2Δ, B2Σ−, and C2Σ+), C2 (d3Πg), and atomic Br (4DJ and 4PJ) were observed in the nascent emission spectra. Free radicals such CHBr or CHCl were also successfully found using laser-induced dispersed fluorescence spectroscopy. The reactive intermediate, CHBr, was seen only in the photolysis of CHBr3, whereas CHCl was only discovered when the precursor was CHBr2Cl or CHBrCl2. More experiments including the power dependence and temporal waveform measurements were conducted. The present study reports the first direct measurements of the intermediate products in the multiphoton photodissociation reaction of these bromomethanes at 266 nm. Nascent emission spectra following the photolysis at longer near-ultraviolet wavelengths (280 and 355 nm) were also acquired. On the bassis of these results, the multiphoton photodissociation mechanism of these bromomethanes at 266 nm can be confirmed.