Stone SC, Philips LA, Fraser GT, Lovas FJ, Xu LH, Sharpe SW
Department of Chemistry, Cornell University, Ithaca, New York, 14853
J Mol Spectrosc. 1998 Nov;192(1):75-85. doi: 10.1006/jmsp.1998.7664.
High-resolution microwave and infrared molecular-beam spectra have been measured for 1,1,2,2-tetrafluoroethane (HFC134). For the higher energy, polar, C2 symmetry, gauche conformer, microwave spectra have been recorded for the normal and mono-13C isotopomers and analyzed to determine a C-C bond length of 1.512(4) Å, in good agreement with a recent ab initio value (MP2/6-31G**) of 1.515 Å [S. Papasavva, K. H. Illinger, and J. E. Kenny, J. Phys. Chem. 100, 10100-10110 (1996)]. A tunable microwave-sideband CO2 laser and electric-resonance optothermal spectrometer have been used to measure the infrared spectrum of the nu6, C-C stretch of the gauche conformer near 906 cm-1. Microwave-infrared double resonance and precise ground state combination differences provided by the microwave measurements guide the assignment of the spectrum. The observation of a c-type spectrum definitively establishes that the upper state vibration is of A symmetry in the C2 point group. The spectrum is fit to a Watson asymmetric-top Hamiltonian to a standard deviation of 0.24 MHz. A weak perturbation shifts the line positions for transitions near J = Kc = 20 by as much as 12 MHz. The identity of the perturber is unknown. Pulsed slit-jet diode-laser spectra have been recorded for the nu16 vibration of the anti conformer near 1127 cm-1. An a- and c-type hybrid band is observed, consistent with a Bu symmetry mode. Previous low-resolution studies have attributed the 1127-cm-1 mode to either a Bu or an Au symmetry vibration. A total of 522 nonblended transitions were assigned and fit to determine ground and excited state constants. The ground state constants of A = 5134.952(65) MHz, B = 3148.277(27) MHz, and C = 2067.106(43) MHz are the first experimental determinations of the rotational constants for this conformer. Here, type A standard uncertainties are given in the parentheses. Copyright 1998 Academic Press.
已对1,1,2,2 - 四氟乙烷（HFC134）进行了高分辨率微波和红外分子束光谱测量。对于能量较高的极性C2对称 gauche构象体，已记录了正常和单 - 13C同位素异构体的微波光谱，并进行分析以确定C - C键长为1.512(4) Å，与最近的从头算值（MP2/6 - 31G**）1.515 Å [S. Papasavva, K. H. Illinger, and J. E. Kenny, J. Phys. Chem. 100, 10100 - 10110 (1996)] 高度吻合。已使用可调谐微波边带CO2激光器和电共振光热光谱仪测量了gauche构象体在906 cm-1附近的ν6，C - C伸缩振动的红外光谱。微波测量提供的微波 - 红外双共振和精确的基态组合差异指导了光谱的归属。观察到c型光谱明确确定了C2点群中高能级振动具有A对称性。该光谱拟合到沃森非对称陀螺哈密顿量，标准偏差为0.24 MHz。一个弱微扰使J = Kc = 20附近跃迁的谱线位置偏移多达12 MHz。微扰体的身份未知。已记录了反式构象体在1127 cm-1附近的ν16振动的脉冲狭缝 - 射流二极管激光光谱。观察到一个a型和c型混合带，与B u对称模式一致。先前的低分辨率研究将1127 cm-1模式归因于B u或A u对称振动。总共指定并拟合了522条非混合跃迁以确定基态和激发态常数。基态常数A = 5134.952(65) MHz，B = 3148.277(27) MHz，C = 2067.106(43) MHz是该构象体转动常数的首次实验测定值。此处，括号内给出的是A类标准不确定度。版权所有1998年，学术出版社。
