The internal conversion of photo-excited pyrazine, which occurs rapidly on a time scale of about 20 fs, has long been considered to proceed via a conical intersection between the optically bright S₂ (¹B_2u, ππ^∗) and dark S₁ (¹B_3u, nπ^∗) states. Since 2008, several theoretical studies have raised the possibility that other dark states S₃ (¹A_u, nπ^∗) and S₄ (¹B_2g, nπ^∗) may participate dominantly in the early stage of the nonradiative decay of S₂. To clarify this issue, being motivated by the recent pump–probe experiment by Horio et al. [J. Chem. Phys. 145 (2016) 044306], we calculated vacuum ultraviolet photoelectron spectra for ionization from each of the four excited states. Comparison was made with the measured time-resolved photoelectron spectrum exhibiting a temporally varying multi-band structure. We confirmed no contribution of S₃ or S₄ and thus the validity of the conventional two-state (S₂ → S₁) picture for ultrafast nonradiative transition in pyrazine.

长期以来，人们一直认为光激发的吡嗪的内部转换是在光学上明亮的S ₂（¹ B _2u，ππ ^∗）和黑暗的S ₁（¹ B _3u，nπ ^∗）状态。自2008年以来，一些理论研究提出了其他暗态S ₃（¹ A _u，nπ ^∗）和S ₄（¹ B _2g，nπ ^∗）的可能性^。）可能主要参与S ₂的非辐射衰变的早期阶段。为了澄清这个问题，受Horio等人最近进行的泵浦探针实验的推动。[J. 化学 物理 145（2016）044306]，我们从四个激发态的每一个计算了用于离子化的真空紫外光电子能谱。与显示出随时间变化的多带结构的所测量的时间分辨光电子光谱进行比较。我们确认没有S ₃或S _4的贡献，因此确认了传统的两态（S ₂  →S ₁ ）照片对于吡嗪中超快非辐射跃迁的有效性。