Takayanagi Toshiyuki, Asakura Tomoko, Motegi Haruki
Department of Chemistry, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama City, Saitama 338-8570, Japan.
J Phys Chem A. 2009 Apr 23;113(16):4795-801. doi: 10.1021/jp808885x.
The lowest electronically adiabatic potential energy surface of the uracil anion has been theoretically investigated with density-functional theory methods in order to understand the mechanism of the N-H bond dissociation induced by low-energy electron attachment. We found that the BH&HLYP level can reasonably describe both the dipole-bound and valence anionic states in a balanced way. With this density-functional theory level, we have constructed two-dimensional potential energy surfaces as a function of appropriate internal coordinates and discuss the importance of electronic coupling between the dipole-bound and valence anion states in dissociative electron attachment of uracil. The transition state geometry for the electronic isomerization between the dipole-bound anion and the pi* valence anion was successfully optimized and the barrier height for this isomerization was found to be relatively low. It was found that the out-of-plane motion of H at the C6 position plays the most important role in this isomerization process. Reduced-dimensionality quantum wave packet calculations taking two active internal coordinates into account have also been performed to interpret the resonance structures observed in cross sections for the N-H dissociation channel at a qualitative level.
为了理解低能电子附着诱导的N-H键解离机制，采用密度泛函理论方法对尿嘧啶阴离子的最低电子绝热势能面进行了理论研究。我们发现，BH&HLYP水平能够以一种平衡的方式合理地描述偶极束缚态和价阴离子态。基于此密度泛函理论水平，我们构建了作为适当内部坐标函数的二维势能面，并讨论了尿嘧啶解离电子附着过程中偶极束缚态和价阴离子态之间电子耦合的重要性。成功优化了偶极束缚阴离子与π*价阴离子之间电子异构化的过渡态几何结构，发现该异构化的势垒高度相对较低。结果表明，C6位置的H原子的面外运动在该异构化过程中起最重要作用。还进行了考虑两个活性内部坐标的降维量子波包计算，以定性解释在N-H解离通道截面中观察到的共振结构。
