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The excited-state intramolecular hydrogen abstraction reactions of butanal have been investigated using the CAS-MP2/6-311+G*//CASSCF/6-31G* methods. Calculated results show that the hydrogen transfer induced fluorescence quenching of the n,π*-excited state of covalent butanal with three paths: (1) The first path corresponds to direct S0-react reconstitution, which involves the first S1 decay by partial hydrogen atom transfer. (2) The second stepwise mechanism can be viewed as a full hydrogen atom transfer followed by a partial hydrogen atom back transfer, electron transfer (near S1/S0 or S0-TS) and finally a proton transfer to S0-react. (3) On the triplet surface, the surface crossing to the singlet state would be clearly much efficient at the T1/S0 region due to the large SOC value of 8.3 cm-1. The S0-react decay route from T1/S0 was studied with an intrinsic reaction coordinate (IRC) calculation at the CASSCF level, resulting in the S0-React minimum.
The excited-state intramolecular hydrogen abstraction reactions of butanal have been investigated using the CAS-MP2 / 6-311 + G * // CASSCF / 6-31G * methods. Calculated results show that the hydrogen transfer induced fluorescence quenching of the n, π * -exited state of covalent butanal with three paths: (1) The first path corresponds to direct S0-react reconstitution, which involves the first S1 decay by partial hydrogen atom transfer. (2) The second stepwise mechanism can be viewed as a full hydrogen atom transfer followed by a partial hydrogen atom back transfer, electron transfer (near S1 / S0 or S0-TS) and finally a proton transfer to SO-react. (3) On the triplet surface, the surface crossing to the singlet state would The S0-react decay route from T1 / S0 was studied with an intrinsic reaction coordinate (IRC) calculation at the CASSCF level, resulting in the S0-React minimum.