The pure rotational spectrum of the less stable conformer of methyl vinyl ether has been measured in an electric-resonance optothermal spectrometer. Analysis of the microwave spectrum shows that the less stable conformer is effectively planar with a low barrier between two gauche forms of the conformer. The rotational constants for the high-energy conformer, obtained from a least-squares fit to a threefold barrier internal rotation Hamiltonian are A = 39 192.490(26) MHz, B = 4527.5496(39) MHz, and C = 4181.2146(43) MHz. The threefold barrier to internal rotation is determined to be V3 = 427.516(71) cm-1. The dipole moment for the conformer has been measured using the Autler-Townes splitting of states in a strong, resonant microwave field. The dipole moment is µtot = 1.9(2) D [µa = 1.3(1) D, µb = 1.4(1) D]. The effectively planar structure of the conformer and the magnitude of the dipole moment are in good agreement with previous ab initio calculations. The experimentally determined threefold barrier to methyl rotation of the present study also agrees well with the value calculated from ab initio methods, 515 cm-1. Copyright 1999 Academic Press.

中文翻译：

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甲基乙烯基醚不稳定构象体旋转光谱的分子束电共振光热光谱研究

甲基乙烯基醚不太稳定的构象异构体的纯旋转光谱已在电共振光热光谱仪中测量。微波光谱分析表明，不太稳定的构象异构体是有效的平面，构象异构体的两种形式之间具有低势垒。从三重势垒内旋转哈密顿量的最小二乘拟合获得的高能构象异构体的旋转常数为 A = 39 192.490(26) MHz、B = 4527.5496(39) MHz 和 C = 4181.2146(43) MHz . 内部旋转的三重障碍被确定为 V3 = 427.516(71) cm-1。构象异构体的偶极矩已使用强共振微波场中的 Autler-Townes 状态分裂进行测量。偶极矩为 µtot = 1.9(2) D [µa = 1.3(1) D, µb = 1.4(1) D]。构象异构体的有效平面结构和偶极矩的大小与之前的 ab initio 计算非常一致。本研究通过实验确定的甲基旋转三重障碍也与从 ab initio 方法计算的值 515 cm-1 非常吻合。版权所有 1999 学术出版社。