Two HCl-Elimination Channels and Two CO-Formation Channels Detected with Time-Resolved Infrared Emission upon Photolysis of Acryloyl Chloride [CH2CHC(O)Cl] at 193 nm

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• 作者：Pei-Wen Lee ; Preston G. Scrape ; Laurie J. Butler ; Yuan-Pern Lee
• 刊名：Journal of Physical Chemistry A
• 出版年：2015
• 出版时间：July 16, 2015
• 年：2015
• 卷：119
• 期：28
• 页码：7293-7304
• 全文大小：626K
• ISSN：1520-5215

文摘

Following photodissociation of gaseous acryloyl chloride, CH₂CHC(O)Cl, at 193 nm, temporally resolved vibration鈥搑otational emission spectra of HCl (v 鈮?7, J 鈮?35) in region 2350鈥?250 cm^鈥? and of CO (v 鈮?4, J 鈮?67) in region 1865鈥?300 cm^鈥? were recorded with a step-scan Fourier-transform spectrometer. The HCl emission shows a minor low-J component for v 鈮?4 with average rotational energy E_rot = 9 卤 3 kJ mol^鈥? and vibrational energy E_vib = 28 卤 7 kJ mol^鈥? and a major high-J component for v 鈮?7 with average rotational energy E_rot = 36 卤 6 kJ mol^鈥? and vibrational energy E_vib = 49 卤 9 kJ mol^鈥?; the branching ratio of these two channels is 鈭?.2:0.8. Using electronic structure calculations to characterize the transition states and each intrinsic reaction coordinate, we find that the minor pathway corresponds to the four-center HCl-elimination of CH₂ClCHCO following a 1,3-Cl-shift of CH₂CHC(O)Cl, whereas the major pathway corresponds to the direct four-center HCl-elimination of CH₂CHC(O)Cl. Although several channels are expected for CO produced from the secondary dissociation of C₂H₃CO and H₂C鈺怌鈺怌鈺怬, each produced from two possible dissociation channels of CH₂CHC(O)Cl, the CO emission shows a near-Boltzmann rotational distribution with average rotational energy E_rot = 21 卤 4 kJ mol^鈥? and average vibrational energy E_vib = 10 卤 4 kJ mol^鈥?. Consideration of the branching fractions suggests that the CO observed with greater vibrational excitation might result from secondary decomposition of H₂C鈺怌鈺怌鈺怬 that was produced via the minor low-J HCl-elimination channel, while the internal state distributions of CO produced from the other three channels are indistinguishable. We also introduce a method for choosing the correct point along the intrinsic reaction coordinate for a roaming HCl elimination channel to generate a Franck鈥揅ondon prediction for the HCl vibrational energy.