環硫乙烯和1,3環硫丙烷光游離解離動態學：門檻光電子光離子同現質譜研究與量子理論計算研究

Abstract

本論文利用門檻光電子光離子同現質譜技術和量子理論G3方法的計算，研究環硫乙烯和1,3環硫丙烷光游離解離動態學。我們由環硫乙烯在光能量範圍10.6-11.8 eV的同現質譜譜線的面積和半高寬，得到c-C2H4S+、CH3CS+和HCS+在各個光能量的分枝比和釋放的平均動能。實驗中觀察到環硫乙烯離子解離成CH3CS+ + H的解離通道釋放出大量的平均動能，並採用G3計算預測環硫乙烯離子的解離通道，推測環硫乙烯離子異構化至次穩定態CH3CSH+結構，再經過渡態結構，斷裂S-H鍵生成C2H3S+和H，同時釋放出大量的動能。另一方面，形成HCS+ + CH3解離通道線性擬合的門檻値10.99 ± 0.04 eV與G3計算値11.05 eV一致，釋放的平均動能與統計計算値相當吻合，以理論計算推測解離途徑也顯示此解離通道沒有逆反應能障。 我們由1,3環硫丙烷在光能量範圍10.2-10.9 eV的同現質譜譜線的飛行時間和半高寬，得到c-C3H6S+和H2CS+在各個光能量的分枝比，和唯一的解離通道H2CS+ + C2H4釋放的平均動能。實驗値和統計方法的準平衡理論的預測平均動能相吻合；G3的解離門檻預測値10.35 eV與線性擬合的實驗値10.41 ± 0.05 eV相符，我們也預測解離途徑，顯示完成此反應途徑無逆反應能障，和c-C2H4S解離形成HCS+ + CH3的情形相似。

Dissociations of energy-selected c-C2H4S+ and c-C3H6S+ were investigated with a threshold photoelectron photoion coincidence technique and quantum-chemical calculations with Gaussian-3 method. For dissociation of c-C2H4S+ in a region 10.6□11.8 eV, branching ratios and average releases of kinetic energy in channels of formation of c-C2H4S+, CH3CS+ and HCS+ were obtained from well-resolved coincidence mass spectra. A large releases of kinetic energy for channel CH3CS++ H of least energy might result from a dissociation mechanism according to which c-C2H4S+ isomerizes to a local minimum CH3CSH+ and then dissociates through a transition state to form CH3CS++ H. On the other hand, a predicted dissociation energy 11.05 eV for c-C2H4S □ HCS+ + CH3 agrees with a linearly extrapolated threshold at 10.99 □ 0.04 eV and a predicted dissociation mechanism that c-C2H4S+ isomerizes to CH3CHS+ before dissociating to HCS+ + CH3 supports the experimental results. For dissociation of c-C3H6S+ in a region ~10.2□10.9 eV, only dissociation channel H2CS+ + C2H4 was observed. Measured average releases of kinetic energy agree satisfactorily with statistical calculations near the appearance threshold; a predicted dissociation energy 10.35 eV for this channel also agrees with a linearly extrapolated threshold at 10.41 □ 0.05 eV. Plausible dissociation mechanisms of c-C3H6S+ to form H2CS+ + C2H4 was reported on the basis of experimental results and G3 calculations.