Sivaranjana Reddy V, Venkatesan T S, Mahapatra S
School of Chemistry, University of Hyderabad, Hyderabad 500 046, India.
J Chem Phys. 2007 Feb 21;126(7):074306. doi: 10.1063/1.2434978.
Photodetachment spectroscopy of phenide anion C6H5- is theoretically studied with the aid of electronic structure calculations and quantum dynamical simulations of nuclear motion. The theoretical results are compared with the available experimental data. The vibronic structure of the first, second, and third photoelectron bands associated with the ground X 2A1 and low-lying excited A 2B1 and B 2A2 electronic states of the phenyl radical C6H5 is examined at length. While the X state of the radical is energetically well separated and its interaction is found to be rather weak with the rest, the A and B electronic states are found to be only approximately 0.57 eV apart in energy at the vertical configuration. Low-energy conical intersections between the latter two states are discovered and their impact on the nuclear dynamics underlying the second and third photoelectron bands is delineated. The nuclear dynamics in the X state solely proceeds through the adiabatic path and the theoretically calculated vibrational level structure of this state compares well with the experimental result. Two Condon active totally symmetric (a1) vibrational modes of ring deformation type form the most dominant progression in the first photoelectron band. The existing ambiguity in the assignment of these two vibrational modes is resolved here. The A-B conical intersections drive the nuclear dynamics via nonadiabatic paths, and as a result the second and third photoelectron bands overlap and particularly the third band due to the B state of C6H5 becomes highly diffused and structureless. Experimental photodetachment spectroscopy results are not available for these bands. However, the second band has been detected in electronic absorption spectroscopy measurements. The present theoretical results are compared with these absorption spectroscopy data to establish the nonadiabatic interactions between the A and B electronic states of C6H5.
借助电子结构计算和核运动的量子动力学模拟，对苯阴离子C6H5-的光剥离光谱进行了理论研究。将理论结果与现有的实验数据进行了比较。详细研究了与苯基自由基C6H5的基态X 2A1以及低激发态A 2B1和B 2A2电子态相关的第一、第二和第三光电子能带的振转结构。虽然自由基的X态在能量上分离良好，且发现其与其他态的相互作用相当弱，但发现A和B电子态在垂直构型下能量仅相差约0.57 eV。发现了后两个态之间的低能锥形交叉点，并描述了它们对第二和第三光电子能带背后的核动力学的影响。X态中的核动力学仅通过绝热路径进行，该态的理论计算振动能级结构与实验结果吻合良好。两种环变形类型的完全对称（a1）振动模式构成了第一光电子能带中最主要的跃迁。这里解决了这两种振动模式归属上存在的模糊性。A - B锥形交叉点通过非绝热路径驱动核动力学，结果第二和第三光电子能带重叠，特别是由于C6H5的B态导致的第三能带变得高度弥散且无结构。目前尚无这些能带的实验光剥离光谱结果。然而，在电子吸收光谱测量中已检测到第二能带。将当前的理论结果与这些吸收光谱数据进行比较，以确定C6H5的A和B电子态之间的非绝热相互作用。
