Theoretical Chemistry, Institute of Physical Chemistry, University of Heidelberg, Im Neuenheimer Feld 229, D-69120 Heidelberg, Germany.
J Chem Phys. 2011 Oct 21;135(15):154310. doi: 10.1063/1.3651536.
There has been a substantial amount of theoretical investigations on the photodynamics of pyrrole, often relying on surface hopping techniques or, if fully quantal, confining the study to the lowest two or three singlet states. In this study we extend ab initio based quantum dynamical investigations to cover simultaneously the lowest five singlet states, two π-σ∗ and two π-π∗ excited states. The underlying potential energy surfaces are obtained from large-scale MRCI ab initio computations. These are used to extract linear and quadratic vibronic coupling constants employing the corresponding coupling models. For the N-H stretching mode Q(24) an anharmonic treatment is necessary and also adopted. The results reveal a sub-picosecond internal conversion from the S(4) (π-π∗) state, corresponding to the strongly dipole-allowed transition, to the S(1) and S(2) (π-σ∗) states and, hence, to the ground state of pyrrole. The significance of the various vibrational modes and coupling terms is assessed. Results are also presented for the dissociation probabilities on the three lowest electronic states.
已有大量关于吡咯光动力学的理论研究，这些研究通常依赖于表面跳跃技术，或者如果是完全量子的，则将研究局限于最低的两个或三个单重态。在这项研究中，我们扩展了基于从头算的量子动力学研究，以同时覆盖最低的五个单重态、两个π-σ∗和两个π-π∗激发态。基础势能面是通过大规模的 MRCI 从头算计算获得的。这些被用来利用相应的耦合模型提取线性和二次振子耦合常数。对于 N-H 伸缩模式 Q(24)，需要采用非谐处理，并且也被采用。结果揭示了从 S(4)（π-π∗）态到 S(1)和 S(2)（π-σ∗）态的亚皮秒内的内部转换，这对应于强烈的偶极允许跃迁，然后是吡咯的基态。评估了各种振动模式和耦合项的重要性。还给出了三个最低电子态上的离解概率的结果。
