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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Microwave Spectrum, r0 Structure, Dipole Moment, Barrier to Internal Rotation, and Ab Initio Calculations for Fluoromethylsilane
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Microwave Spectrum, r0 Structure, Dipole Moment, Barrier to Internal Rotation, and Ab Initio Calculations for Fluoromethylsilane

机译：氟甲基硅烷的微波光谱，r0结构，偶极矩，内旋壁垒和从头算

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摘要

The microwave spectra of seven isotopomers of fluoromethylsilane, CH2FSiH3, in the ground vibrational state were measured and analyzed in the frequency range 18-40 GHz. The rotational and centrifugal distortion constants were evaluated by the least-squares treatment of the observed frequencies of a- and b-type R- and b-type Q-transitions. The values for the components of the dipole moment were obtained from the measurements of Stark effects from both a- and b-type transitions and the determined values are: |μa| ) 1.041(5), |μb| ) 1.311(6), and |μt| ) 1.674(4) D. Structural parameters have been determined and the heavy atom distances (r0) in Angstroms are: Si-C ) 1.8942(57) and C-F ) 1.4035(55) and the angle in degree, ∠SiCF ) 109.58(14). A semi-experimental re structure was also determined from experimental ground state rotational constants and vibration-rotation constants derived from ab initio force fields. The internal torsional fundamental, SiH3, was observed at 149.2 cm-1 with two accompanying hot bands at 138.8 and 127.5 cm-1. The barrier to internal rotation was obtained as 717.3(16) cm-1 (2.051(46) kcal mol-1) by combining the analysis of the microwave A and E splittings and the torsional fundamental and hot band frequencies. Ab initio calculations have been carried out with full electron correlation by the second-order perturbation method with several different basis sets up to MP2/6-311+G(d,p) to obtain geometrical parameters, barriers to internal rotation, and centrifugal distortion constants. Adjusted r0 structural parameters have been obtained by combining the ab initio MP2/6-311+G(d,p) predicted values with the determined rotational constants for the fluoride as well as with the previously reported microwave data for the chloro- and bromo- compounds. These experimental results are compared to the corresponding parameters for the carbon analogues.
机译：在18-40 GHz的频率范围内，对七种氟甲基硅烷CH2FSiH3的异构体的微波光谱进行了测量和分析。通过最小二乘法对观察到的a型和b型R型和b型Q转变的频率进行评估，以评估旋转和离心变形常数。偶极矩分量的值是从a型和b型跃迁的Stark效应的测量值获得的，确定的值为：|μa|。 ）1.041（5），|μb| ）1.311（6）和|μt| ）1.674（4）D.确定了结构参数，以埃为单位的重原子距离（r0）为：Si-C）1.8942（57）和CF）1.4035（55）以及度数角∠SiCF）109.58（ 14）。还根据实验的基态旋转常数和从头算力场得出的振动-旋转常数确定了半实验性的重构结构。在149.2 cm-1处观察到内部扭转基波SiH3，并在138.8和127.5 cm-1处出现两个伴随的热带。通过结合微波A和E分裂的分析以及扭转基带和热带频率，获得了内部旋转的屏障，为717.3（16）cm-1（2.051（46）kcal mol-1）。已经通过二阶摄动方法，使用具有MP2 / 6-311 + G（d，p）的几种不同基本设置的二阶摄动方法，以全电子相关性进行了从头计算，以获得几何参数，内部旋转的障碍和离心畸变常数。调整后的r0结构参数是通过从头算起MP2 / 6-311 + G（d，p）预测值与确定的氟化物旋转常数以及先前报道的氯和溴的微波数据相结合而获得的化合物。将这些实验结果与碳类似物的相应参数进行比较。

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