环丙酮光解离和热异构机理的从头算研究

Ab initio Study on Mechanisms of Photodissociation and Thermal Isomerization of Cyclopropanone

运用精确的量子化学计算方法CASSCF,B3LYP和MP2,结合cc-pVDZ基组,优化了环丙酮的基态和激发态势能面上的驻点结构,计算了它们的相对能量.在此基础上,深入探讨了环丙酮光解离反应的机理.在292～365nm波长的光的激发下,环丙酮被激发至S1态,最可能的初始过程是αC—C键断裂.我们的理论研究发现,在αC—C键断裂途径上,存在基态和第一激发势能面的交叉点,它在随后的反应过程中起着重要作用.一方面可形成单态双自由基中间体,然后发生另一个C—C键的断裂,生成基态产物一氧化碳和乙烯.另一方面,经过S1/S0交叉点可以回到热的基态.在这种情况下,体系具有足够的能量,克服基态途径上的势垒,生成同样的基态产物乙烯和一氧化碳.此外,还对环丙酮基态异构化反应进行了理论研究.

In the present work, the potential energy profiles, governing the dissociation of cyclopropanone to CO＋C2H4 in the S0, S1 and T1 states, have been determined using complete active space self-consistent field （CASSCF）, density functional theory （DFT）, and the second-order Moller-Plesset perturbation theory （MP2） in conjugation with the correlation-consistent atomic natural orbital basis set, cc-pVDZ. Upon photoexcitation in the range of 292～365 nm, the initial process was determined to be the α C-C bond cleavage after the cyclopropanone was excited to the S1 state. Our research found that the S1/S0 intersection point played an important role in the subsequent processes. On one hand, the singlet diradical is produced as an intermediate, which is followed by formation of CO and CH2=CH2 in the S0 state. On the other hand, the ＂hot＂ parent molecule can be formed through the S1/S0 intersection point, which has enough internal energies to overcome the barrier on the pathway to CO and CH2=CH2. Besides, the isomerization reactions of cyclopropanone in the ground state were investigated in this work.