Biswas Partha, Panja Sujit S, Manogaran S, Chakraborty Tapas
Department of Chemistry, Indian Institute of Technology Kanpur, UP 208016 India.
J Phys Chem A. 2005 Apr 14;109(14):3225-34. doi: 10.1021/jp045383s.
Laser-induced fluorescence excitation and resolved fluorescence spectra following excitations of the single vibronic levels (SVL) of p-vinyltoluene (p-VT) and p-vinylfluorobenzene (p-VFB) have been measured in a seeded supersonic free-jet expansion. A complete vibronic assignment of the fluorescence spectrum measured following excitation of the 0(0)0-band of p-VT has been presented. Normal vibrational modes in the S0 and S1 states of the molecule have been calculated by CASSCF method, and the correlation between the two set of modes is made by expressing the excited-state normal modes in terms of those of the ground state. The calculations predict that in the excited state methyl and vinyl torsional motions of p-VT are extensively mixed with many of the out-of-plane modes of the aromatic ring. Our resolved fluorescence spectral data measured following SVL excitations essentially agree with such predictions. In the excited state, the molecule exhibits a dramatically low threshold for the rotor-induced IVR in a supersonic jet expansion. Several mechanisms have been discussed to explain the phenomenon.
在种子超声速自由射流膨胀中，测量了对乙烯基甲苯（p-VT）和对乙烯基氟苯（p-VFB）的单振动能级（SVL）激发后的激光诱导荧光激发光谱和分辨荧光光谱。给出了对p-VT的0(0)0带激发后测量的荧光光谱的完整振转归属。通过CASSCF方法计算了分子基态S0和激发态S1的正常振动模式，并通过将激发态正常模式用基态模式表示来建立两组模式之间的关联。计算预测，在激发态下，p-VT的甲基和乙烯基扭转运动与芳环的许多面外模式广泛混合。我们在SVL激发后测量的分辨荧光光谱数据基本与这些预测一致。在激发态下，该分子在超声速射流膨胀中表现出极低的转子诱导内禀振动弛豫阈值。已经讨论了几种机制来解释这一现象。
