Knowledge Bank

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 (CHBr$3$, CHBr$2$Cl, CHBrCl$2$, CH$2$Br$2$, CHI$3$, CH$2$I$2$, and CH$3$I), several excited species such as CH (A$2\Delta$, B$2\Sigma -$, and C$2\Sigma +$), atomic Br or I, and C$2$ (d$3\Pi g$) 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 ~{A}$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}A\prime \prime$(0,v$2$,0)$\leftarrow$~{X}$\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}A\prime$(0,0,0) transitions. Interestingly, CHBr was seen only in the photolysis of CHBr$3$, whereas CHCl was only discovered when the precursor is CHBr$2$Cl or CHBrCl$2$. 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 (CHBr$3$, CHBr$2$Cl, CHBrCl$2$, and CH$2$Br$2$) and that of iodomethanes (CHI$3$, CH$2$I$2$, and CH$3$I). Our recent progress will be presented.