School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom.
J Chem Phys. 2011 Nov 21;135(19):194307. doi: 10.1063/1.3659231.
Time-resolved photoelectron spectroscopy was used to obtain new information about the dynamics of electronic relaxation in gas-phase indole and 5-hydroxyindole following UV excitation with femtosecond laser pulses centred at 249 nm and 273 nm. Our analysis of the data was supported by ab initio calculations at the coupled cluster and complete-active-space self-consistent-field levels. The optically bright (1)L(a) and (1)L(b) electronic states of (1)ππ∗ character and spectroscopically dark and dissociative (1)πσ∗ states were all found to play a role in the overall relaxation process. In both molecules we conclude that the initially excited (1)L(a) state decays non-adiabatically on a sub 100 fs timescale via two competing pathways, populating either the subsequently long-lived (1)L(b) state or the (1)πσ∗ state localised along the N-H coordinate, which exhibits a lifetime on the order of 1 ps. In the case of 5-hydroxyindole, we conclude that the (1)πσ∗ state localised along the O-H coordinate plays little or no role in the relaxation dynamics at the two excitation wavelengths studied.
采用时间分辨光电子能谱技术，利用中心波长为 249nm 和 273nm 的飞秒激光脉冲对吲哚和 5-羟基吲哚的气相分子进行激发，获得了关于其电子弛豫动力学的新信息。我们通过耦合簇和完全活性空间自洽场水平的从头算计算，对数据进行了分析。具有（1）ππ∗特征的光学明亮（1）L(a)和（1）L(b)电子态，以及光谱上暗的和离解的（1）πσ∗态，都被发现对整体弛豫过程起到了作用。在这两个分子中，我们推断初始激发的（1）L(a)态通过两条竞争途径非绝热地衰减，在 100fs 以内，要么弛豫到随后的长寿命（1）L(b)态，要么弛豫到沿 N-H 坐标局域的（1）πσ∗态，其寿命约为 1ps。在 5-羟基吲哚的情况下，我们推断沿 O-H 坐标局域的（1）πσ∗态在研究的两个激发波长下对弛豫动力学几乎没有或没有作用。
