Scuola Normale Superiore, Piazza dei Cavalieri, 7 I-56126 Pisa, Italy.
Chemphyschem. 2011 Jul 11;12(10):1957-68. doi: 10.1002/cphc.201001080. Epub 2011 May 3.
A quantum mechanical study of the interplay between the bright ππ*(S(π)) and the dark nπ*(S(n)) excited states of thymine in the gas phase is reported. TD-PBE0 calculations indicate that within a relevant region of the S(π) surface, connecting the Franck-Condon point with the planar and non-planar S(π) plateau, S(π) and S(n) are almost isoenergetic and that a S(π)→S(n) population transfer is therefore likely. This latter process has been studied by two complementary quantum dynamical approaches, a three-dimensional anharmonic (quartic) model, and a full-dimensional harmonic linear vibronic coupling model. Although providing slightly different quantitative indications, both approaches predict a very fast and effective S(π)→S(n) population transfer: already at 50 fs the S(n) state is significantly populated (20-40%) and this population persists or even increases on a longer time scale.
报道了气相中天冬嘧啶的亮ππ*（S(π)）和暗 nπ*（S(n)）激发态之间相互作用的量子力学研究。TD-PBE0 计算表明，在 S(π)表面的一个相关区域内，连接 Franck-Condon 点与平面和非平面 S(π)平台，S(π)和 S(n)几乎等能量，因此 S(π)→S(n)的种群转移很可能发生。后一种过程已通过两种互补的量子动力学方法进行了研究，即三维非谐（四次）模型和全维谐波线性耦合模型。尽管提供了略有不同的定量指示，但两种方法都预测了非常快速和有效的 S(π)→S(n)种群转移：在 50 fs 时，S(n)态已显著占据（20-40%），并且这种种群在较长时间尺度上持续存在甚至增加。
