Jensen E T
Department of Physics, University of Northern BC, 3333 University Way, Prince George B.C., V2N 4Z9, Canada.
Phys Chem Chem Phys. 2021 Feb 19;23(6):3748-3760. doi: 10.1039/d0cp05844k.
The mechanisms for photodissociation of methyl halides (CH3X, X = Cl, Br, I) have been studied for these molecules when adsorbed on thin films of C6H6 or C6F6 on copper single crystals, using time-of-flight spectroscopy with 248 nm and 193 nm light. For CH3Cl and CH3Br monolayers adsorbed on C6H6, two photodissociation pathways can be identified - neutral photodissociation similar to the gas-phase, and a dissociative electron attachment (DEA) pathway due to photoelectrons from the metal. The same methyl halides adsorbed on a C6F6 thin film display only neutral photodissociation, with the DEA pathway entirely absent due to intermolecular quenching via a LUMO-derived electronic band in the C6F6 thin film. For CH3I adsorbed on a C6F6 thin film, illumination with 248 nm light results in CH3 photofragments departing due to neutral photodissociation via the A-band absorption. When CH3I monolayers on C6H6 thin films are illuminated at the same wavelength, additional new photodissociation pathways are observed that are due to absorption in the molecular film with energy transfer leading to dissociation of the CH3I molecules adsorbed on top. The proposed mechanism for this photodissociation is via a charge-transfer complex for the C6H6 layer and adsorbed CH3I.
利用248纳米和193纳米光的飞行时间光谱，研究了吸附在铜单晶上的苯（C6H6）或六氟苯（C6F6）薄膜上的卤代甲烷（CH3X，X = Cl、Br、I）分子的光解离机制。对于吸附在C6H6上的CH3Cl和CH3Br单层，可识别出两种光解离途径——类似于气相的中性光解离，以及由于来自金属的光电子导致的解离电子附着（DEA）途径。吸附在C6F6薄膜上的相同卤代甲烷仅显示中性光解离，由于通过C6F6薄膜中源自最低未占分子轨道（LUMO）的电子能带进行分子间猝灭，DEA途径完全不存在。对于吸附在C6F6薄膜上的CH3I，用248纳米光照射会导致CH3光碎片通过A带吸收因中性光解离而离开。当以相同波长照射C6H6薄膜上的CH3I单层时，会观察到额外的新光解离途径，这是由于分子薄膜中的吸收以及能量转移导致顶部吸附的CH3I分子解离。这种光解离的 proposed机制是通过C6H6层和吸附的CH3I形成的电荷转移复合物。 （注：原文中“proposed”未翻译完整，推测可能是“提出的”之类意思，结合语境补充完整了译文）
