Photodissociation dynamics of methanol at 157 nm

Photofragment time-of-flight (TOF) spectra at m/e = 1(H), 2(H-2, D), 3(HD), and 4(D-2) have been measured for CH3OH, CH3OD, and CD3OH at 157 nm excitation, TOF spectra for photofragments at m/e = 12, 13, 14, 15, 29, 30 from the photodissociation of CH3OH at 157 nm were also obtained. Analysis of these experimental results reveals three different atomic H loss processes: one type of direct hydroxyl H elimination and two types of methyl H elimination. Experimental results also indicate that two molecular hydrogen elimination channels are present: 3-center elimination from the methyl group, which displays two different micro-pathways, and 4-center elimination involving hydrogen atoms on both the C and O sites. The relative branching of the atomic versus molecular hydrogen elimination channels was found to be 1:0.21, indicating that the atomic hydrogen process is still much more significant than the molecular hydrogen process. The C-O bond cleavage channel was also experimentally observed. These results present a uniquely clear picture of methanol photodissociation at 157 nm and thus provide an excellent case for quantitative theoretical investigations.