15min:

CHEN-NAN LIU, HSIANG-FU LIAO, GUANG-YI HOU, SHI-XING YANG AND BOR-CHEN CHANG, Department of Chemistry, National Central University, Jhongli 32001, Taiwan.

Emission spectroscopy including nascent emission and laser-induced dispersed fluorescence was adopted to investigate the multiphoton photolysis mechanism of halomethanes at near-ultraviolet wavelengths in a slow flow system. In the 266 nm photolysis of the interested halomethanes (CHBr₃, CHBr₂Cl, CHBrCl₂, CH₂Br₂, CHI₃, CH₂I₂, and CH₃I), several excited species such as CH (A² , B^{2 -}, and C^{2 +}), atomic Br or I, and C₂ (d³ _g) were observed in the nascent emission spectra. Halomethylenes (CHX, X= Br, Cl, I), the reactive intermediates, were not observed in nascent emission spectra, but they can be found using laser-induced dispersed fluorescence spectroscopy following excitation of their ùA''(0,v₂,0) X¹A'(0,0,0) transitions. Interestingly, CHBr was seen only in the photolysis of CHBr₃, whereas CHCl was only discovered when the precursor is CHBr₂Cl or CHBrCl₂. The photolysis laser power dependence and emission waveform measurements were also conducted. In addition, nascent emission spectra following the photolysis at longer near-ultraviolet wavelengths (280 nm and 355 nm) were acquired. The results show the distinctive differences between the photolysis of bromomethanes (CHBr₃, CHBr₂Cl, CHBrCl₂, and CH₂Br₂) and that of iodomethanes (CHI₃, CH₂I₂, and CH₃I). Our recent progress will be presented.