Equilibrium Structures of Heterocyclic Molecules with Large Principal Axis Rotations upon Isotopic Substitution

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• 作者：Jean Demaison ; Attila G. Cs谩sz谩r ; Laurent D. Margul猫s ; Heinz Dieter Rudolph
• 刊名：Journal of Physical Chemistry A
• 出版年：2011
• 出版时间：December 8, 2011
• 年：2011
• 卷：115
• 期：48
• 页码：14078-14091
• 全文大小：955K
• 年卷期：v.115,no.48(December 8, 2011)
• ISSN：1520-5215

文摘

Equilibrium structures, r_e, of the heterocyclic molecules oxirane, furazan, furan, ethylene ozonide, and 1,3,4-oxadiazole have been determined using three different, somewhat complementary techniques: a completely experimental technique (r_m), a semiexperimental technique (r_e^SE, whereby equilibrium rotational constants are derived from experimental effective ground-state rotational constants and corrections based principally on an ab initio cubic force field), and an ab initio technique (r_e^BO, whereby geometry optimizations are usually performed at the coupled cluster level of theory including single and double excitations augmented by a perturbational estimate of the effects of connected triple excitations [CCSD(T)] using quadruple-味 Gaussian basis sets). All these molecules are asymmetric tops with the moment of inertia I_c much larger than the other two moments of inertia, I_a and I_b. Molecules of this shape experience a large rotation of the principal axis system upon certain isotopic substitutions. For such isotopologues it is difficult to obtain a good structural fit to the semiexperimental moments of inertia I_a and I_b, which may significantly reduce the accuracy of the r_e^SE structural parameters. The origin of this difficulty is explained. For the heavy-atom skeleton of these molecules it was possible to determine a rather accurate empirical mass-dependent structure without a priori knowledge of the equilibrium structure.