Molecular Structure of Methyldifluoroisocyanato Silane: A Combined Microwave Spectral and Theoretical Study

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• 作者：Gamil A. Guirgis ; Jason S. Overby ; Michael H. Palmer ; Rebecca A. Peebles ; Sean A. Peebles ; Lena F. Elmuti ; Daniel A. Obenchain ; Brooks H. Pate ; Nathan A. Seifert
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：August 2, 2012
• 年：2012
• 卷：116
• 期：30
• 页码：7822-7829
• 全文大小：352K
• 年卷期：v.116,no.30(August 2, 2012)
• ISSN：1520-5215

文摘

The structure of methyldifluoroisocyanato silane, MeF₂SiNCO (2), has been studied by molecular rotational spectroscopy. The rotational spectrum has a complicated structure from ¹⁴N nuclear quadrupole coupling and internal rotation of the methyl group. Cavity Fourier-transform microwave spectroscopy measurements were important for providing high spectral resolution to analyze the quadrupole and internal rotation fine structure. Broadband chirped-pulse Fourier-transform microwave spectroscopy was used to achieve high measurement sensitivity making it possible to observe the lower abundance C, N, O, and Si isotopologues in natural abundance for structure determination. Analysis of the microwave spectrum of the most abundant isotopomer of MeF₂SiNCO (2) yields the rotational constants: A = 3827.347(7), B = 1264.5067(14), and C = 1240.6182(11) MHz. The spectrum has been analyzed in the I^r representation for C_s symmetry, with inclusion of the 3-fold rotor (V₃ = 446(50) cm^鈥?). A partial substitution structure was obtained for the C, Si, N, and O atoms. The analysis was assisted by calculations of the equilibrium structure, using a 6-311++G (3df, 3pd) basis set, with calculations at each of the B3LYP, MP2, and CCSD(T) levels. The calculated and experimental rotational constants are only consistent with a trans-orientation at each of the HCSiN, CSiNC, and SiNCO centers; there is relatively close agreement between the experimental and the theoretical structures, especially at the CCSD(T) level. In addition, the observed low value for the ¹⁴N quadrupole coupling term (蠂_bb 鈥?蠂_cc) implies a wide SiNC angle, which is consistent with the calculated values: 165.3掳 (B3LYP), 157.6掳 (MP2), and 157.4掳 (CCSD(T)). The skeletal bending potential is discussed.