本研究係以全初始化理論計算及密度泛函理論，進行巴豆醛分子於單重態及三重態位能面下之解離及異構化反應途徑研究。對於各反應物、中間物、產物及過渡態結構方面，使用 B3LYP 方法搭配 6-311++G(d,p) 基底函數組來進行幾何結構之最佳化計算，並以 CCSD(T) 方法搭配 6-311G(d,p) 基底函數組進行較精確之單點能量計算，同時採用 B3LYP/6-311++G(d,p) 之振動頻率計算結果，進行零點振動能量之校正，並針對五個解離途徑進行研究：(1) 氫原子途徑、(2) 甲醛基途徑、(3) 甲基途徑、(4) 一氧化碳途徑、及 (5) 甲醛分子途徑進行研究，以及對其中四個同分異構物：(1) 1,3-丁二烯醇、(2) 3-丁烯醛、(3) 乙基乙烯酮、及 (4) CH3CHCH2CO 進行相關之研究。於單重態位能面上，巴豆醛分子具有四種幾何異構物，並可進行解離反應產生丙烯及一氧化碳或丙炔及甲醛。而在異構化途徑方面，巴豆醛分子可直接異構化至 3-丁烯醛或先異構化成 1,3-丁二烯醇再異構化至 3-丁烯醛。巴豆醛分子之第一激發態為 n → pi* 之躍遷，其能量約為 357.9 kJ/mol，而其第二激發態為 pi → pi* 之躍遷，其能量約為 579.2 kJ/mol。而位於激發態之巴豆醛分子應可藉由跨電子系統轉移之弛緩途徑至 3T (pp*) 及 3T (np*)，而由於三重態位能面之異構物較多，因此在三重態位能面上可找到更多之反應路徑。藉由計算所得，發現在單重態及三重態位能面，異構化途徑之能障均比分解途徑低。

Decomposition and isomerization pathways on both singlet and triplet surfaces of crotonaldehyde are investigated using quantum chemical calculations. The geometries of intermediates, transition states, and dissociation products involved in these electronic surfaces are optimized and their energetics are obtained at B3LYP/6-311++G(d,p) level. The accurate energies are further calculated at level CCSD(T)/6-311G(d,p) base on the optimized geometries. Five primary dissociation pathways are found: (i) H-atom, (ii) HCO, (iii) CH3, (iv) CO, and (v) H2CO elimination and four isomerization channels are correlated: (i) 1,3-butadienol, (ii) 3-butenal, (iii) ethylketene, and (iv) CH3CHCH2CO. On the singlet surface, crotonaldehyde exhibits four conformers: E-s-trans, E-s-cis Z-s-trans, and Z-s-cis. The main dissociation channels are C3H6 + CO and C3H4 + H2CO. Direct isomerization to 3-butenal is obtained to have an energy threshold 344 kJ/mol or can be formed from isomer 1,3-butadienol first with a threshold 146 kJ/mol via a two-step process. The first electronic excited singlet state is an n-p* transition at about 357.9 kJ/mol above the ground state and the second excited state a p-p* transition at 579.2 kJ/mol above. When crotonaldehyde is excited to the S2 state it undergoes rapid internal conversion to the S1 surface. Then the molecule can either relax to the 3T (pp*) surface from intersystem crossing then to 3T (np*) via the conical intersection or internally convert to the S0 surface. From the results of calculations for the triplet and singlet surfaces isomerization processes have lower energy thresholds than those for the dissociation channels. Hence for photochemical reactions of crotonaldehyde, isomerization process should be the major channel.

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