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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >X-tilde~1A_1, a-tilde~3B_1, and A-tilde~1B_1 States of SiCl_2: Ab Initio Calculations and Simulation of Emission Spectra
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X-tilde~1A_1, a-tilde~3B_1, and A-tilde~1B_1 States of SiCl_2: Ab Initio Calculations and Simulation of Emission Spectra

机译：SiCl_2的X-tilde〜1A_1，a-tilde〜3B_1和A-tilde〜1B_1状态：从头算计算和发射光谱模拟

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A variety of correlated molecular orbital methods and basis sets have been employed to obtain the minimumenergy geometries, harmonic vibrational frequencies, and relative energies of the X-tilde~1A_1, a-tilde~3B_1, and A-tilde~1B_1 states of SiCl_2. The ab initio results obtained have been comnpared with experimental values, where available. It was found that ab initio methods which are based on unrestricted-spin (UHF) wave functions employing spin-unprojected energies, including the QCISD(T) and CCSD(T) methods and the composite methods of G1 and G2, failed to give a reliable A-tilde~1B_1-X-tilde~1A-tilde_1 separation, whereas methods using spin-projected energies or the restricted multireference method MR-CISD/6-311G (2df) gave relable A-tilde-X-tilde and a-tilde-X-tilde separations. The A-tilde~1B_1-X-tilde~1A-tilde_1 and a-tilde~3B_1-X-tilde~1A_1 emission spectra of SiCl_2 were simulated, employing MP2/6-311G (2df) force constants and compared with available experimental spectra. The geometry of the X-tilde state was held fixed at the geometry determined by microwave spectroscopy, and the geometries of the a-tilde~3B_1 and A-tilde~1B_1 states were adjusted via an iterative Franck-Condon analysis (IFCA) procedure until the simulated spectra matched best with the observed spectra. The IFCA derived geometry for the A-tilde~1B_1 state is r(SiCl) = 2.055 +- 0.008 A and #theta#(ClSiCl) = 119.4 deg +- 0.4 dge. For the a-tilde~3B_1 state, r(SiCl) = 2.041 +- 0.005 A, while the (ClSiCl) angle can have a value of either 115.4 deg or 114.5 deg, depending on the vibrational assignments of the experimental spectra.
机译：已经使用各种相关的分子轨道方法和基集来获得SiCl_2的X-tilde〜1A_1，a-tilde〜3B_1和A-tilde〜1B_1状态的最小能量几何形状，谐波振动频率和相对能量。从头开始的结果已与实验值（如果有）进行了比较。发现基于自旋非投影能量的无限制自旋（UHF）波函数的从头算方法，包括QCISD（T）和CCSD（T）方法以及G1和G2的复合方法，未能给出结论。可靠的A-tilde〜1B_1-X-tilde〜1A-tilde_1分离，而使用自旋投影能量的方法或受限多参考方法MR-CISD / 6-311G（2df）给出了可靠的A-tilde-X-tilde和a-波浪线X波浪线分隔。利用MP2 / 6-311G（2df）力常数模拟了SiCl_2的A-tilde〜1B_1-X-tilde〜1A-til_1和a-tilde〜3B_1-X-tilde〜1A_1发射光谱，并与可用的实验光谱进行了比较。 X-波浪形的几何形状保持固定，由微波光谱法确定，通过迭代弗兰克-康登分析（IFCA）程序调整a-tilde〜3B_1和A-tilde〜1B_1状态的几何形状，直到模拟光谱与观察光谱最匹配。 IFCA得出的A-tilde〜1B_1状态的几何形状为r（SiCl）= 2.055 +-0.008 A和＃theta＃（ClSiCl）= 119.4度±0.4 dge。对于a-tilde〜3B_1状态，r（SiCl）= 2.041 +-0.005 A，而（ClSiCl）角的值可以为115.4度或114.5度，具体取决于实验光谱的振动分配。

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