Newby Josh J, Liu Ching-Ping, Müller Christian W, Zwier Timothy S
Department of Chemistry, Purdue University, West Lafayette, IN 47907-2084, USA.
Phys Chem Chem Phys. 2009 Oct 1;11(37):8316-29. doi: 10.1039/b903827b. Epub 2009 Jul 7.
The vibronic excitation spectrum of phenylcyclopenta-1,3-diene (PCP3D) has been recorded in a supersonic expansion using resonant-two-photon ionization (R2PI) and laser-induced fluorescence (LIF) techniques. The spectrum is dominated by the S(0)-S(1) origin transition (31,739 cm(-1)), with several low-frequency vibronic bands in the first 400 cm(-1), followed by a sharp cut-off in intensity due to turn-on of a non-radiative process. Single vibronic level fluorescence (SVLF) spectra were recorded for the S(1) origin and several vibronic bands of PCP3D. The excitation and emission spectra show that the molecule is planar with C(s) symmetry in both the ground and excited states. Torsional potentials were simulated from the observed torsional structure in the excitation and emission spectra. The S(0) potential (V(2) = 1237 cm(-1), V(4) = -256 cm(-1)) is associated with a flat-bottomed potential supporting large inter-ring angular changes with little cost in energy (+/-36 degrees at 200 cm(-1)), with a barrier of 1237 cm(-1) at the perpendicular geometry. The S(1) potential is much stiffer about the planar geometry, with a calculated barrier five times larger than in S(0) (V(2) = 6732 cm(-1), V(4) = -477 cm(-1)). Based on the torsional assignments, weak bands in the same frequency region assigned earlier to the structural isomer phenylcyclopenta-1,4-diene [J. J. Newby, J. A. Stearns, C. P. Liu and T. S. Zwier, J. Phys. Chem. A, 2007, 111, 10914-10927] have been re-assigned as hot bands arising from v'' = 1 in the inter-ring torsion, nu(57).
利用共振双光子电离（R2PI）和激光诱导荧光（LIF）技术，在超声速膨胀条件下记录了苯基环戊 - 1,3 - 二烯（PCP3D）的振转激发光谱。该光谱以S(0)-S(1)起始跃迁（31,739 cm⁻¹）为主，在前400 cm⁻¹内有几个低频振转带，随后由于非辐射过程的开启，强度急剧截止。记录了PCP3D的S(1)起始态和几个振转带的单振子能级荧光（SVLF）光谱。激发光谱和发射光谱表明，该分子在基态和激发态均具有C(s)对称性的平面结构。根据在激发光谱和发射光谱中观察到的扭转结构模拟了扭转势能。S(0)势能（V(2) = 1237 cm⁻¹，V(4) = -256 cm⁻¹）与一个平底势能相关，支持大环间角度的大幅变化且能量成本很小（在200 cm⁻¹时为±36°），在垂直几何构型处有1237 cm⁻¹的势垒。S(1)势能在平面几何构型附近要硬得多，计算出的势垒比S(0)中的大五倍（V(2) = 6732 cm⁻¹，V(4) = -477 cm⁻¹）。基于扭转归属，先前归属于结构异构体苯基环戊 - 1,4 - 二烯[J. J. 纽比、J. A. 斯特恩斯、C. P. 刘和T. S. 兹维尔，《物理化学杂志A》，2007年，111卷，10914 - 10927页]的同一频率区域内的弱带已被重新归属于环间扭转ν(57)中v'' = 1产生的热谱带。
