Fourier transform microwave spectrum and ab initio study of dimethyl methylphosphonate
Fourier transform microwave spectrum and ab initio study of dimethyl methylphosphonate
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DOI：
10.1006/jmsp.2001.8486
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发表时间：
2002-01-01
影响因子：
1.4
通讯作者：
Samuels, AC
中科院分区：
文献类型：
--
作者：
Suenram, RD;Lovas, FJ;Samuels, AC
使用脉冲分子束傅立叶变换微波光谱仪研究了甲基膦酸二甲酯 (DMMP) 的旋转光谱。分子中三个甲基顶部的内旋转运动以及两个甲氧基的相互转化运动使光谱变得复杂。在这里，我们介绍了微波谱、从头计算以及分子刚性转子 A 对称态的分配。此状态的旋转常数为 A = 2828.753(2) MHz、B = 1972.360(3) MHz 和 C = 1614.267(2) MHz。在下面的论文中，我们对 DMMP 进行了群论分析。观察到的分子构象不具有点群对称性，所有三种电偶极子选择规则均有效，其中 c 型跃迁最为强烈。从头计算在 Hartree-Fock 6-31G* 和 MP2/6-311G* 理论水平上进行。这些计算表明两个低能量构象可能被小于 170 cm(-1) 的能量分开。此外，计算出的最低能量构象异构体与实验观察到的一致。两种低能构象异构体的相对能量从HF水平的34 cm(-1)上升到MP2水平的170 cm(-1)。 (C) 2002 年爱思唯尔科学。
The rotational spectrum of dimethyl methylphosphonate (DMMP) has been studied using a pulsed molecular beam Fourier transform microwave spectrometer. The spectrum is complicated by the internal rotation motions of the three methyl tops in the molecule as well as an interconversion motion of the two methoxy groups. Here, we present the microwave spectrum, the ab initio calculations, and the assignment of the rigid-rotor A-symmetry state of the molecule. The rotational constants for this state are A = 2828.753(2) MHz, B = 1972.360(3) MHz, and C = 1614.267(2) MHz. In the following paper, a group theoretical analysis is developed for DMMP. The observed conformation of the molecule has no point-group symmetry and all three electric-dipole selection rules are active, with c-type transitions being the most intense. Ab initio calculations were carried out at both the Hartree-Fock 6-31G* and MP2/6-311G* levels of theory. These calculations indicate that two low-energy conformations are possible separated by energies of less than 170 cm(-1). Furthermore, the calculated lowest energy conformer is in agreement with the one observed experimentally. The relative energies of the two low-energy conformers rise from 34 cm(-1) at the HF level to 170 cm(-1) at the MP2 level. (C) 2002 Elsevier Science.