Müller Christian, Klöppel-Riech Michael, Schröder Frauke, Schroeder Jörg, Troe Jürgen
Institut für Physikalische Chemie der Universität, Tammannstr. 6, D-37077 Göttingen, Germany.
J Phys Chem A. 2006 Apr 20;110(15):5017-31. doi: 10.1021/jp060366j.
We investigated the spectroscopy of the first excited singlet electronic state S1 of 2-phenylindene using both fluorescence excitation spectroscopy and resonantly enhanced multiphoton ionization spectroscopy. Moreover, we investigated the dynamics of the S1 state by determining state-selective fluorescence lifetimes up to an excess energy of approximately 3400 cm(-1). Ab initio calculations were performed on the torsional potential energy curve and the equilibrium and transition state geometries and normal-mode frequencies of the first excited singlet state S1 on the CIS level of theory. Numerous vibronic transitions were assigned, especially those involving the torsional normal mode. The torsional potentials of the ground and first excited electronic states were simulated by matching the observed and calculated torsional frequency spacings in a least-squares fitting procedure. The simulated S1 potential showed very good agreement with the ab initio potential calculated on the CIS/6-31G(d,p) level of theory. TDDFT energy corrections improved the match with the simulated S(1) torsional potential. The latter calculation yielded a torsional barrier of V2 = 6708 cm(-1), and the simulation a barrier of V2 = 6245 cm(-1). Ground-state normal-mode frequencies were calculated on the B3LYP/6-31G(d,p) level of theory, which were used to interpret the infrared spectrum, the FDS spectrum of the transition and hot bands of the FES spectrum. The fluorescence intensities of the nu49 overtone progression could reasonably be reproduced by considering the geometry changes upon electronic excitation predicted by the ab initio calculations. On the basis of the torsional potential calculations, it could be ruled out that the uniform excess energy dependence of the fluorescence lifetimes is linked to the torsional barrier in the excited state. The rotational band contour simulation of the transition yielded rotational constants in close agreement to the ab initio values for both electronic states. Rotational coherence signals were obtained by polarization-analyzed, time-resolved measurements of the fluorescence decay of the transition. The simulation of these signals yielded corroborating evidence as to the quality of the ab initio calculated rotational constants of both states. The origin of the anomalous intensity discrepancy between the fluorescence excitation spectrum and the REMPI spectrum is discussed.
我们使用荧光激发光谱和共振增强多光子电离光谱研究了2-苯基茚的第一激发单重态S1的光谱。此外，我们通过确定高达约3400 cm(-1)过剩能量的态选择性荧光寿命来研究S1态的动力学。在CIS理论水平上对第一激发单重态S1的扭转势能曲线、平衡态和过渡态几何结构以及简正模式频率进行了从头算。确定了许多振转跃迁，特别是那些涉及扭转简正模式的跃迁。通过最小二乘法拟合程序匹配观测到的和计算出的扭转频率间距，模拟了基态和第一激发电子态的扭转势能。模拟的S1势能与在CIS/6-31G(d,p)理论水平上计算的从头算势能非常吻合。TDDFT能量校正改善了与模拟的S(1)扭转势能的匹配。后一种计算得出扭转势垒V2 = 6708 cm(-1)，模拟得出的势垒为V2 = 6245 cm(-1)。在B3LYP/6-31G(d,p)理论水平上计算了基态简正模式频率，用于解释红外光谱、FES光谱的跃迁和热带的FDS光谱。通过考虑从头算预测的电子激发时的几何结构变化，可以合理地再现ν49泛频进展的荧光强度。基于扭转势能计算，可以排除荧光寿命的均匀过剩能量依赖性与激发态扭转势垒有关。跃迁的转动带轮廓模拟得出的转动常数与两个电子态的从头算值非常吻合。通过对跃迁荧光衰减进行偏振分析、时间分辨测量获得转动相干信号。这些信号的模拟为两个态的从头算计算转动常数的质量提供了确证。讨论了荧光激发光谱和REMPI光谱之间异常强度差异的起源。
