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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Rotational spectrum and conformational composition of cyanoacetaldehyde, a compound of potential prebiotic and astrochemical interest
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Rotational spectrum and conformational composition of cyanoacetaldehyde, a compound of potential prebiotic and astrochemical interest

机译：氰基乙醛的旋转光谱和构象组成

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摘要

The rotational spectrum of cyanoacetaldehyde (NCCH _2CHO) has been investigated in the 19.5-80.5 and 150-500 GHz spectral regions. It is found that cyanoacetaldehyde is strongly preferred over its tautomer cyanovinylalcohol (NCCH=CHOH) in the gas phase. The spectra of two rotameric forms of cyanoacetaldehyde produced by rotation about the central C-C bond have been assigned. The C-C-C-O dihedral angle has an unusual value of 151(3)° from the synperiplanar (0°) position in one of the conformers denoted I, while this dihedral angle is exactly synperiplanar in the second rotamer called II, which therefore has C _s symmetry. Conformer I is found to be preferred over II by 2.9(8) kJ/mol from relative intensity measurements. A double minimum potential for rotation about the central C-C bond with a small barrier maximum at the exact antiperiplanar (180°) position leads to Coriolis perturbations in the rotational spectrum of conformer I. Selected transitions of I were fitted to a Hamiltonian allowing for this sort of interaction, and the separation between the two lowest vibrational states was determined to be 58794(14) MHz [1.96112(5) cm ~(-1)]. Attempts to include additional transitions in the fits using this Hamiltonian failed, and it is concluded that it lacks interaction terms to account satisfactorily for all the observed transitions. The situation was different for II. More than 2000 transitions were assigned and fitted to the usual Watson Hamiltonian, which allowed very accurate values to be determined not only for the rotational constants, but for many centrifugal distortion constants as well. Two vibrationally excited states were also assigned for this form. Theoretical calculations were performed at the B3LYP, MP2, and CCSD levels of theory using large basis sets to augment the experimental work. The predictions of these calculations turned out to be in good agreement with most experimental results.
机译：氰基乙醛（NCCH _2CHO）的旋转光谱已在19.5-80.5和150-500 GHz光谱区域中进行了研究。发现在气相中，氰基乙醛比其互变异构体氰基乙烯基醇（NCCH ＝ CHOH）更优选。已经指定了通过绕中心C-C键旋转而产生的两种旋转异构形式的氰基乙醛的光谱。在表示为I的一个构象异构体中，CCCO二面角与上平面（0°）的位置之间的异常值为151（3）°，而在称为II的第二旋转异构体中，该二面角恰好在上平面，因此具有C _s对称性。从相对强度测量中发现，符合标准品I比标准品II高2.9（8）kJ / mol。围绕中心CC键旋转的最小双倍势能，在精确的反周平面（180°）位置具有较小的势垒最大值，会导致构象异构体I的旋转谱中出现科里奥利扰动。I的选定跃迁适合于哈密顿量，可以进行这种分类相互作用，两个最低振动状态之间的间隔确定为58794（14）MHz [1.96112（5）cm〜（-1）]。使用此哈密顿量尝试在拟合中包括其他过渡的尝试失败了，并且得出的结论是，它缺少交互项来令人满意地解释所有观察到的过渡。 II的情况有所不同。已为通常的Watson Hamiltonian分配了超过2000个过渡并将其拟合，从而不仅可以确定非常精确的值，而且不仅可以确定旋转常数，还可以确定许多离心变形常数。还为该形式指定了两个振动激发态。理论计算是在B3LYP，MP2和CCSD的理论水平上进行的，使用大的基础集来扩大实验工作。这些计算的预测结果与大多数实验结果非常吻合。

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