Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, People's Republic of China.
Chemistry College, Beijing Normal University, Beijing 100875, People's Republic of China.
J Chem Phys. 2017 Mar 21;146(11):114305. doi: 10.1063/1.4977763.
The excited-state structural dynamics and the decay mechanism of 2(1H)-pyridinone (NHP) after excitation to the S(2ππ) light-absorbing state were studied using resonance Raman spectroscopy and complete-active space self-consistent field (CASSCF) calculations. The B-band absorption cross-section and the corresponding absolute resonance Raman cross-sections were simulated using a simple model based on time-dependent wave-packet theory. The geometric structures of the singlet electronic excited states and their curve-crossing points were optimized at the CASSCF level of theory. The obtained short-time structural dynamics in easy-to-visualize internal coordinates were then compared with the CASSCF-predicted structural-parameter changes of S(2ππ)/S(2nπ)-MIN, S(2ππ)/S(1nπ)-MIN, and S(2ππ)-MIN. Our results indicate that the initial population of NHP in the S state bifurcates in or near the Franck-Condon region, leading to two predominant (SS-MIN and SS-MIN) internal conversion pathways. The lowest-lying S(1ππ) excited state is finally formed via subsequent internal conversions S(2nπ)/S(1ππ)-MIN and S(1nπ)/S(1ππ)-MIN. The enol-keto tautomeric mechanism does not seem to play a role. The decay mechanism in the singlet realm is proposed.
采用共振拉曼光谱和完全活性空间自洽场（CASSCF）计算研究了 2（1H）-吡啶酮（NHP）在激发到 S（2ππ）光吸收态后的激发态结构动力学和衰减机制。基于含时波包理论的简单模型模拟了 B 带吸收截面和相应的绝对共振拉曼截面。在 CASSCF 理论水平上优化了单重态电子激发态的几何结构及其曲线交叉点。然后，将获得的易于可视化的内坐标的短时间结构动力学与 CASSCF 预测的 S（2ππ）/S（2nπ）-MIN、S（2ππ）/S（1nπ）-MIN 和 S（2ππ）-MIN 的结构参数变化进行了比较。结果表明，NHP 在 S 态的初始布居在 Franck-Condon 区域或其附近分叉，导致两条主要的（SS-MIN 和 SS-MIN）内转换途径。最终通过后续内转换 S（2nπ）/S（1ππ）-MIN 和 S（1nπ）/S（1ππ）-MIN 形成最低的 S（1ππ）激发态。烯醇-酮互变异构机制似乎不起作用。提出了单重态衰减机制。
