Department of Chemistry, University of Missouri - Kansas City, Kansas City, Missouri 64110-2499, USA.
J Phys Chem A. 2010 Apr 1;114(12):4131-7. doi: 10.1021/jp911614d.
The microwave spectra of seven isotopomers of fluoromethylsilane, CH(2)FSiH(3), 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: |mu(a)| = 1.041(5), |mu(b)| = 1.311(6), and |mu(t)| = 1.674(4) D. Structural parameters have been determined and the heavy atom distances (r(0)) in Angstroms are: Si-C = 1.8942(57) and C-F = 1.4035(55) and the angle in degree, angleSiCF = 109.58(14). A semi-experimental r(e) structure was also determined from experimental ground state rotational constants and vibration-rotation constants derived from ab initio force fields. The internal torsional fundamental, SiH(3), 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 r(0) 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.
七氟甲基硅烷 CH(2)FSiH(3) 的七种同位素的微波光谱在基态振动能级下进行了测量和分析，频率范围为 18-40GHz。通过对 a-和 b-型 R-和 b-型 Q-跃迁的观测频率进行最小二乘处理，评估了旋转和离心畸变常数。通过对 a-和 b-型跃迁的斯塔克效应的测量得到了偶极矩分量的值，确定的值为：|mu(a)| = 1.041(5)，|mu(b)| = 1.311(6)，|mu(t)| = 1.674(4) D。结构参数已经确定，重原子距离（r(0)）以埃为单位：Si-C = 1.8942(57)，C-F = 1.4035(55)，角度 SiCF = 109.58(14)。还从实验基态旋转常数和从从头算力场得出的振动-旋转常数确定了半经验 r(e)结构。SiH(3)的内部扭转基频在 149.2cm(-1)处观测到，两个伴随的热带分别在 138.8cm(-1)和 127.5cm(-1)处。通过结合微波 A 和 E 分裂以及扭转基频和热带频率的分析，得到了内部旋转的势垒为 717.3(16)cm(-1)（2.051(46) kcal mol(-1))。通过二阶微扰法与几种不同的基组进行全电子相关计算，直至 MP2/6-311+G(d,p)，得到了几何参数、内部旋转势垒和离心畸变常数。通过将从头算 MP2/6-311+G(d,p)预测值与氟化物的确定旋转常数以及先前报道的氯代和溴代化合物的微波数据相结合，获得了调整后的 r(0)结构参数。将这些实验结果与碳类似物的相应参数进行了比较。
