Sun Ge, Zheng Xianfeng, Song Yu, Zhou Weidong, Zhang Jingsong
Department of Chemistry, University of California at Riverside, Riverside, California 92521, USA.
J Chem Phys. 2023 Sep 14;159(10). doi: 10.1063/5.0166757.
The photodissociation dynamics of jet-cooled ethyl radical (C2H5) via the Ã2A'(3s) states are studied in the wavelength region of 230-260 nm using the high-n Rydberg H-atom time-of-flight (TOF) technique. The H + C2H4 product channels are reexamined using the H-atom TOF spectra and photofragment translational spectroscopy. A prompt H + C2H4(X̃1Ag) product channel is characterized by a repulsive translational energy release, anisotropic product angular distribution, and partially resolved vibrational state distribution of the C2H4(X̃1Ag) product. This fast dissociation is initiated from the 3s Rydberg state and proceeds via a H-bridged configuration directly to the H + C2H4(X̃1Ag) products. A statistical-like H + C2H4(X̃1Ag) product channel via unimolecular dissociation of the hot electronic ground-state ethyl (X̃2A') after internal conversion from the 3s Rydberg state is also examined, showing a modest translational energy release and isotropic angular distribution. An adiabatic H + excited triplet C2H4(ã3B1u) product channel (a minor channel) is identified by energy-dependent product angular distribution, showing a small translational energy release, anisotropic angular distribution, and significant internal excitation in the C2H4(ã3B1u) product. The dissociation times of the different product channels are evaluated using energy-dependent product angular distribution and pump-probe delay measurements. The prompt H + C2H4(X̃1Ag) product channel has a dissociation time scale of <10 ps, and the upper bound of the dissociation time scale of the statistical-like H + C2H4(X̃1Ag) product channel is <5 ns.
利用高里德堡氢原子飞行时间（TOF）技术，在230 - 260 nm波长区域研究了喷射冷却的乙基自由基（C2H5）通过Ã2A'(3s)态的光解离动力学。使用氢原子TOF光谱和光碎片平动光谱对H + C2H4产物通道进行了重新研究。一个快速的H + C2H4(X̃1Ag)产物通道的特征是平动能释放具有排斥性、产物角分布呈各向异性以及C2H4(X̃1Ag)产物的振动状态分布部分可分辨。这种快速解离从3s里德堡态开始，通过一个氢桥构型直接生成H + C2H4(X̃1Ag)产物。还研究了一个类似统计的H + C2H4(X̃1Ag)产物通道，它是在从3s里德堡态内转换后，热电子基态乙基（X̃2A'）单分子解离产生的，表现出适度的平动能释放和各向同性角分布。通过能量依赖的产物角分布确定了一个绝热的H + 激发三重态C2H4(ã3B1u)产物通道（一个次要通道），其平动能释放较小、角分布呈各向异性且C2H4(ã3B1u)产物有显著的内部激发。使用能量依赖的产物角分布和泵浦 - 探测延迟测量来评估不同产物通道的解离时间。快速的H + C2H4(X̃1Ag)产物通道的解离时间尺度小于10 ps，类似统计的H + C2H4(X̃1Ag)产物通道的解离时间尺度上限小于5 ns。
