McCann Kathleen, Wagner Martin, Guerra Aaron, Coronado Paul, Villarreal J R, Choo Jaebum, Kim Sungwhan, Laane Jaan
Department of Chemistry, Texas A&M University, College Station, TX 77843, USA.
J Chem Phys. 2009 Jul 28;131(4):044302. doi: 10.1063/1.3169504.
The laser-induced fluorescence spectra (both fluorescence excitation and dispersed fluorescence) of jet-cooled 1,3-benzodioxan along with its ultraviolet absorption spectra have been recorded and analyzed in order to determine the vibrational quantum levels in both the ground and S(1)(pi,pi()) electronic excited states. A detailed energy map of the vibrational levels involving the six lowest frequency vibrations was established and utilized to better understand the structural and conformational differences between the ground and excited electronic states. The energies of more than a dozen vibrational excited states involving the out-of-plane ring twisting (nu(47)) and the out-of-plane ring bending (nu(48)) modes were determined for both S(0) and S(1) electronic states. Ab initio and density functional theory (DFT) calculations were also carried out to complement the experimental work. The data allowed one-dimensional potential energy functions in terms of the ring-twisting coordinate to be calculated. These show the molecule to have a twisting angle of 33 degrees and a barrier to planarity of 4300+/-500 cm(-1) for the S(0) ground state and an angle of 24 degrees and a barrier of 1500+/-200 cm(-1) for the S(1)(pi,pi()) excited state.
为了确定基态和S(1)(π,π*)电子激发态的振动量子能级，已记录并分析了喷射冷却的1,3 - 苯并二恶烷的激光诱导荧光光谱（包括荧光激发光谱和色散荧光光谱）及其紫外吸收光谱。建立了涉及六个最低频率振动的振动能级的详细能量图，并利用该图更好地理解基态和激发电子态之间的结构和构象差异。确定了S(0)和S(1)电子态中涉及面外环扭转（ν(47)）和面外环弯曲（ν(48)）模式的十多个振动激发态的能量。还进行了从头算和密度泛函理论（DFT）计算以补充实验工作。这些数据使得能够根据环扭转坐标计算一维势能函数。结果表明，对于S(0)基态，分子的扭转角为33度，平面化势垒为4300±500 cm(-1)；对于S(1)(π,π*)激发态，扭转角为24度，势垒为1500±200 cm(-1)。
