Kaneshima Keisuke, Ninota Yuki, Sekikawa Taro
Opt Express. 2018 Nov 12;26(23):31039-31054. doi: 10.1364/OE.26.031039.
We report the first time-resolved high-harmonic spectroscopy (TR-HHS) study of a chemical bond rearrangement. We investigate the transient change of the high-harmonic signal from 1,3-cyclohexadiene (CHD), which undergoes ring-opening and isomerizes to 1,3,5-hexatriene (HT) upon photoexcitation. We associated the harmonic yield variation with the changes in the molecule's electronic state and vibrational frequencies, which are caused by isomerization. This showed us that the electronic excited state of CHD created through two-photon absorption of 3.1 eV photons relaxes almost completely within 100 fs to the electronic ground state of CHD with vibrational excitation. Subsequently, the molecule isomerizes to HT (i.e., ring-opening occurs, around 400 fs after the excitation). The present results demonstrate that TR-HHS, which can track both electronic and nuclear dynamics, is a powerful tool for studying ultrafast photochemical reactions.
我们报道了首次对化学键重排进行的时间分辨高次谐波光谱（TR-HHS）研究。我们研究了1,3-环己二烯（CHD）高次谐波信号的瞬态变化，该分子在光激发下会发生开环并异构化为1,3,5-己三烯（HT）。我们将谐波产率的变化与分子电子态和振动频率的变化联系起来，这些变化是由异构化引起的。这向我们表明，通过双光子吸收3.1 eV光子产生的CHD电子激发态在100 fs内几乎完全弛豫到具有振动激发的CHD电子基态。随后，分子异构化为HT（即开环发生，在激发后约400 fs）。目前的结果表明，能够追踪电子和核动力学的TR-HHS是研究超快光化学反应的有力工具。
