Imaging Momentum Orbital Densities of Conformationally Versatile Molecules: A Benchmark Theoretical Study of the Molecular and Electronic Structures of Dimethoxymethane

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• 作者：Y. R. Huang ; S. Knippenberg ; B. Hajgat&oacute ; J.-P. Franç ; ois ; J. K. Deng ; M. S. Deleuze
• 刊名：Journal of Physical Chemistry A
• 出版年：2007
• 出版时间：July 5, 2007
• 年：2007
• 卷：111
• 期：26
• 页码：5879 - 5897
• 全文大小：668K
• 年卷期：v.111,no.26(July 5, 2007)
• ISSN：1520-5215

文摘

The main purpose of the present work is to predict from benchmark many-body quantum mechanicalcalculations the results of experimental studies of the valence electronic structure of dimethoxymethaneemploying electron momentum spectroscopy, and to establish once and for all the guidelines that shouldsystematically be followed in order to reliably interpret the results of such experiments on conformationallyversatile molecules. In a first step, accurate calculations of the energy differences between stationary pointson the potential energy surface of this molecule are performed using Hartree-Fock (HF) theory and post-HFtreatments of improving quality (MP2, MP3, CCSD, CCSD(T), along with basis sets of increasing size. Thisstudy focuses on the four conformers of this molecule, namely the trans-trans (TT), trans-gauche (TG),gauche-gauche (G⁺G⁺), and gauche-gauche (G⁺G^-) structures, belonging to the C_2v, C₁, C₂, and C_s symmetrypoint groups, respectively. A focal point analysis supplemented by suited extrapolations to the limit ofasymptotically complete basis sets is carried out to determine how the conformational energy differences at0 K approach the full CI limit. In a second step, statistical thermodynamics accounting for hindered rotationsis used to calculate Gibbs free energy corrections to the above energy differences, and to evaluate the abundanceof each conformer in the gas phase. It is found that, at room temperature, the G⁺G⁺ species accounts for 96%of the conformational mixture characterizing dimethoxymethane. In a third step, the valence one-electronand shake-up ionization spectrum of dimethoxymethane is analyzed according to calculations on the G⁺G⁺conformer alone by means of one-particle Green's function [1p-GF] theory along with the benchmark third-order algebraic diagrammatic construction [ADC(3)] scheme. A complete breakdown of the orbital picture ofionization is noted at electron binding energies above 22 eV. A comparison with available (e,2e) ionizationspectra enables us to identify specific fingerprints of through-space orbital interactions associated with theanomeric effect. At last, based on our 1p-GF/ADC(3) assignment of spectral bands, accurate and sphericallyaveraged (e,2e) electron momentum distributions at an electron impact energy of 1200 eV are computedfrom the related Dyson orbitals. Very significant discrepancies are observed with momentum distributionsobtained for several outer-valence levels using standard Kohn-Sham orbitals.