Experimental and theoretical study of the photodissociation reaction of thiophenol at 243 nm: intramolecular orbital alignment of the phenylthiyl radical.
Experimental and theoretical study of the photodissociation reaction of thiophenol at 243 nm: intramolecular orbital alignment of the phenylthiyl radical.
复制标题
DOI：
10.1063/1.2424939
复制
发表时间：
2007-01
期刊：
影响因子：
--
通讯作者：
Ivan S. Lim;Jeong Sik Lim;Yoon Sup Lee;Sang Kyu Kim
中科院分区：
文献类型：
--
作者：
Ivan S. Lim;Jeong Sik Lim;Yoon Sup Lee;Sang Kyu Kim
用H(D)离子速度图成像技术研究了243 nm泵浦的硫酚(C(6)H(5)SH)或硫酚d(1)(C(6)H(5)SD)的光致脱氢反应。光解产物对应于H(或D)离子图像中观察到的两个不同的各向异性环，被鉴定为苯硫基的两个最低电子态(C(6)H(5)S)。从头算结果表明，苯硫基的单占据分子轨道位于硫原子上，对于基态(B(1))和第一激发态(B(2))物种，它分别垂直于或平行于分子平面.这两个态之间的实验能量间隔为2600+/-200 cm(-1)，与作者在CASPT2水平上的2674 cm(-1)的理论预测非常一致。在D从C(6)H(5)SD解离得到的大平移能下的各向异性参数(β)为-1.0+/-0.0 5，表明在2 43 nm处与这种光学跃迁相关的跃迁偶极矩垂直于解离的S-D键，这反过来又意味着在排斥势能面上存在一个超快的D+C(6)H(5)S(B(1))解离通道.在较小的平动能下观察到的约化各向异性参数为-0.76+/-0.04，这表明D+C(6)H(5)S(B(2))通道可能沿着反应坐标与初始激发态与其他低位电子态的耦合所导致的绝热反应路径进行。采用多参考波函数的详细的高水平从头计算表明，C(6)H(5)S(B(1))通道可以通过243 nm处的a(1)(n(Pi)，sigma(*))光激发直接进入，而C(6)H(5)S(B(2))通道的光解离动力学的主要特征是(3)(n(Pi)，pi(*))->的参与；(3)(n(西格玛)，西格玛(*))分布和自旋轨道避免了地面和(3)(n(Pi)，西格玛(*))态的交叉。准确地估算了苯硫酚-d(1)的S-D键离解能为D(0)=79.6+/-0.3kcalol。S-氢键的解离能也被估算为D(0)=76.8+/-0.3kcalmoL，比以前报道的至少小2kcalmo.发现苯基团的C-H键产生了H片段。由pi-pi(*)n(Pi)-pi(*)跃迁引起的开环反应可能是碎片各向同性宽平动能分布的原因。
The photoinduced hydrogen (or deuterium) detachment reaction of thiophenol (C(6)H(5)SH) or thiophenol-d(1) (C(6)H(5)SD) pumped at 243 nm has been investigated using the H (D) ion velocity map imaging technique. Photodissociation products, corresponding to the two distinct and anisotropic rings observed in the H (or D) ion images, are identified as the two lowest electronic states of phenylthiyl radical (C(6)H(5)S). Ab initio calculations show that the singly occupied molecular orbital of the phenylthiyl radical is localized on the sulfur atom and it is oriented either perpendicular or parallel to the molecular plane for the ground (B(1)) and the first excited state (B(2)) species, respectively. The experimental energy separation between these two states is 2600+/-200 cm(-1) in excellent agreement with the authors' theoretical prediction of 2674 cm(-1) at the CASPT2 level. The experimental anisotropy parameter (beta) of -1.0+/-0.05 at the large translational energy of D from the C(6)H(5)SD dissociation indicates that the transition dipole moment associated with this optical transition at 243 nm is perpendicular to the dissociating S-D bond, which in turn suggests an ultrafast D+C(6)H(5)S(B(1)) dissociation channel on a repulsive potential energy surface. The reduced anisotropy parameter of -0.76+/-0.04 observed at the smaller translational energy of D suggests that the D+C(6)H(5)S(B(2)) channel may proceed on adiabatic reaction paths resulting from the coupling of the initially excited state to other low-lying electronic states encountered along the reaction coordinate. Detailed high level ab initio calculations adopting multireference wave functions reveal that the C(6)H(5)S(B(1)) channel may be directly accessed via a (1)(n(pi),sigma(*)) photoexcitation at 243 nm while the key feature of the photodissociation dynamics of the C(6)H(5)S(B(2)) channel is the involvement of the (3)(n(pi),pi(*))-->(3)(n(sigma),sigma(*)) profile as well as the spin-orbit induced avoided crossing between the ground and the (3)(n(pi),sigma(*)) state. The S-D bond dissociation energy of thiophenol-d(1) is accurately estimated to be D(0)=79.6+/-0.3 kcalmol. The S-H bond dissociation energy is also estimated to give D(0)=76.8+/-0.3 kcalmol, which is smaller than previously reported ones by at least 2 kcalmol. The C-H bond of the benzene moiety is found to give rise to the H fragment. Ring opening reactions induced by the pi-pi(*)n(pi)-pi(*) transitions followed by internal conversion may be responsible for the isotropic broad translational energy distribution of fragments.