Nichols Bethan, Sullivan Erin N, Neumark Daniel M
Department of Chemistry, University of California, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
J Chem Phys. 2020 Jun 28;152(24):244301. doi: 10.1063/5.0006913.
The photodissociation dynamics of the tert-butyl perthiyl (t-BuSS) radical are investigated by fast-beam coincidence translational spectroscopy. A fast (6 keV-8 keV) beam of neutral t-BuSS radicals is produced via photodetachment of the corresponding anion, followed by photodissociation at 248 nm (5.00 eV) or 193 nm (6.42 eV) and coincident detection of the neutral products. Photofragment mass and translational energy distributions are obtained at both wavelengths. At 248 nm, the dominant product channel (90%) is found to be S loss, with a product translational energy distribution that peaks close to the maximum available energy and an anisotropic photofragment angular distribution, indicating dissociation along a repulsive excited state. A minor channel (10%) leading to the formation of S + t-Bu is also observed. At 193 nm, both two- and three-body dissociation are observed. The formation of S + t-Bu is the dominant two-body product channel, with multiple electronic states of the S molecule produced via excited-state dissociation processes. The formation of S + t-BuS is a minor two-body channel at this dissociation energy. The three-body channels are S + H + isobutene, S + CH + propene, and S + SH + isobutene. The first two of these channels result from a sequential dissociation process in which the loss of S from t-BuSS results in ground-state t-Bu with sufficient internal energy to undergo secondary fragmentation. The third three-body channel, S + SH + isobutene, is attributed to the loss of internally excited HS from t-BuSS, which then rapidly dissociates to form S + SH in an asynchronous concerted dissociation process.
通过快束符合平移光谱法研究了叔丁基过硫自由基（t-BuSS）的光解离动力学。通过相应阴离子的光剥离产生快速（6 keV - 8 keV）的中性t-BuSS自由基束，随后在248 nm（5.00 eV）或193 nm（6.42 eV）处进行光解离，并对中性产物进行符合检测。在两个波长下均获得了光碎片质量和平移能量分布。在248 nm处，发现主要产物通道（90%）是硫损失，其产物平移能量分布在接近最大可用能量处达到峰值，且光碎片角分布呈各向异性，表明是沿着排斥激发态进行解离。还观察到一个导致形成S + t-Bu的次要通道（10%）。在193 nm处，观察到了二体解离和三体解离。S + t-Bu的形成是主要的二体产物通道，通过激发态解离过程产生了S分子的多个电子态。在该解离能量下，S + t-BuS的形成是一个次要的二体通道。三体通道为S + H + 异丁烯、S + CH + 丙烯和S + SH + 异丁烯。前两个通道源于一个连续解离过程，其中t-BuSS中硫的损失导致具有足够内能的基态t-Bu发生二次碎片化。第三个三体通道S + SH + 异丁烯归因于t-BuSS中内部激发的HS的损失，然后HS在一个异步协同解离过程中迅速解离形成S + SH。
