Gao Yan, Pemberton Christine C, Zhang Yao, Weber Peter M
Department of Chemistry, Brown University, Providence, Rhode Island 02912, USA.
J Chem Phys. 2016 May 21;144(19):194303. doi: 10.1063/1.4948629.
The ultrafast relaxation pathway of α-terpinene was studied by photoionization-photoelectron spectroscopy for a range of excitation conditions. Time-resolved spectra were obtained upon optical excitation with ultrashort laser pulses at 5.56 eV, 4.96 eV, 4.76 eV, and 4.56 eV, followed by ionization with 3.06 eV pulses. The experiments yielded spectra of the initially excited state, which decays with a time constant of 66 fs, independent of the excitation wavelength. We also observed a sequential series of Rydberg peaks, including the s, p, and d states with n = 3-6, which capture the travel times on the ensuing reaction path. There is no statistically significant dependence of the travel time on the excitation energy. A comparison of the time-dependent signals with those of the un-substituted parent molecule, 1,3-cyclohexadiene, shows that the substituents on α-terpinene slow the reaction down by a factor of about 2.
通过光电离光电子能谱在一系列激发条件下研究了α-萜品烯的超快弛豫途径。用5.56 eV、4.96 eV、4.76 eV和4.56 eV的超短激光脉冲进行光激发，随后用3.06 eV脉冲进行电离，获得了时间分辨光谱。实验得到了初始激发态的光谱，其以66 fs的时间常数衰减，与激发波长无关。我们还观察到一系列连续的里德堡峰，包括n = 3-6的s、p和d态，这些峰记录了后续反应路径上的传播时间。传播时间对激发能量没有统计学上的显著依赖性。将时间相关信号与未取代的母体分子1,3-环己二烯的信号进行比较，结果表明α-萜品烯上的取代基使反应减慢了约2倍。
