| Summary: | 碩士 === 國立交通大學 === 應用化學系碩博士班 === 105 === Photodissociation of methyl formate(HC(O)OCH3) with light at 193 nm and 248 nm has been investigated with a step-scan time-resolved Fourier-transform emission spectrometer. Rotationally-resolved bands in region 1865－2300 cm-1 werw observed and assigned as emission of CO (v≤11,J≤27) and CO(v≤4,J≤25) for the experiment at 248 nm and 193 nm, respectively.
Two different conditions were used for experiments at 248 nm. At low pressure (methyl formate 0.71 torr, Ar 0.16 torr), the average rotational energy is 3.0 ± 0.1 kJ mol-1 and the average vibrational energy is 76 ± 1 kJ mol-1. At high pressure (methyl formate 1 torr, Ar 3 torr), the average rotational energy is 2.4 ± 0.1 kJ mol-1 and the average vibrational energy is 66 ± 1 kJ mol-1. In contrast to Lin’s results[J. Phys. Chem. A. 120, 5155 (2016)], reporting that the rotational distribution of CO is bimodal at v = 1 and v = 2, with the low-J component from the roaming path, our results show that the rotational distribution of CO is Boltzmann in each vibrational state; CO comes from decomposition of HC(O)OCH3 via the conventional TS.
For the experiment at 193 nm, the average rotational energy is 3.6 ± 0.3 kJ mol-1 and the average vibrational energy is 14 ± 2 kJ mol-1. The rotational distribution of CO is Boltzmann in each vibrational state; it was produced via the secondary dissociation of HCO product rather than via the conventional transition-state for decomposition of HC(O)OCH3. A broad emission band of CO2 was observed. The vibrational distribution of CO2 is bimodal and the maximum vibrational energy is 165 kJ mol-1 for channel A and 263 kJ mol-1 for channel B. According to theroetical calculations, CO2 in channel A is produced from the direct decomposition of HC(O)OCH3 via TS7 and CO2 in channel B is from the secondary decomposition of the isomer HOCOCH3 via TS6.
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