Melandri S, Maris A, Favero PG, Favero LB, Caminati W, Meyer R
Dipartimento di Chimica "G. Ciamician" dell'Universita, Via Selmi 2, Bologna, I-40126, Italy;
J Mol Spectrosc. 1997 Oct;185(2):374-83. doi: 10.1006/jmsp.1997.7391.
The rotational spectrum of p-anisaldehyde in a supersonic expansion has been investigated in the frequency range 60-78 GHz. Transitions up to J = 57 measured for the anti and syn conformers have been used to determine complete sets of fourth-order centrifugal distortion constants. Methyl group internal rotation splittings have also been observed for some of the lines and have yielded the respective barriers for both conformers. A vibrational satellite observed for each of the two conformers has been assigned to the respective first excited methoxy torsional state. The jet conditions, in particular the stagnation pressure of the carrier gas, can be adjusted to control the degree of cooling achieved in the expansion. This possibility has been exploited in the present work to enhance the intensities of the observed vibrational satellites. Applying a two-dimensional flexible model to the methoxyl and aldehydic groups torsions, the potential energy and structural deformation parameters transferred from anisole and benzaldehyde have been found to be suitable to describe these motions in p-anisaldehyde. Mixing of anti and syn conformations has been found to be insignificant within the first 82 calculated torsional eigenstates and therefore less likely to explain the intermediate bands observed in the low-resolution microwave spectrum than the internal vibrational relaxation suggested by R. K. Bohn, M. S. Farag, C. M. Ott, J. Radhakrishnan, S. A. Sorenson, and N. S. True (1992, J. Mol. Struct. 268, 107-121). A qualitative discussion of relaxation among the torsional states and its effect on the rotational spectrum is given. Copyright 1997 Academic Press. Copyright 1997Academic Press
在60 - 78GHz频率范围内研究了对甲氧基苯甲醛在超声速膨胀中的转动光谱。已测量了反式和顺式构象高达J = 57的跃迁，用于确定完整的四阶离心畸变常数集。还观察到了一些谱线的甲基内旋转分裂，并得出了两种构象各自的势垒。观察到的两种构象各自的一个振动卫星已被归属到相应的第一激发甲氧基扭转态。喷射条件，特别是载气的滞止压力，可以进行调节以控制膨胀过程中达到的冷却程度。在本工作中利用了这种可能性来增强观察到的振动卫星的强度。将二维柔性模型应用于甲氧基和醛基的扭转，发现从苯甲醚和苯甲醛转移来的势能和结构变形参数适合描述对甲氧基苯甲醛中的这些运动。已发现在计算的前82个扭转本征态内反式和顺式构象的混合不显著，因此与R. K. Bohn、M. S. Farag、C. M. Ott、J. Radhakrishnan、S. A. Sorenson和N. S. True（1992年，《分子结构杂志》268卷，107 - 121页）提出的内振动弛豫相比，不太可能解释在低分辨率微波光谱中观察到的中间谱带。给出了扭转态之间弛豫及其对转动光谱影响的定性讨论。版权所有1997年学术出版社。版权所有1997年学术出版社
