Solvent-Induced Red-Shifts for the Proton Stretch Vibrational Frequency in a Hydrogen-Bonded Complex. 1. A Valence Bond-Based Theoretical Approach

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• 作者：Philip M. Kiefer ; Ehud Pines ; Dina Pines ; James T. Hynes
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：July 17, 2014
• 年：2014
• 卷：118
• 期：28
• 页码：8330-8351
• 全文大小：745K
• ISSN：1520-5207

文摘

A theory is presented for the proton stretch vibrational frequency 谓_AH for hydrogen (H鈭? bonded complexes of the acid dissociation type, that is, AH路路路B A^{鈥?/sup>路路路HB+(but without complete proton transfer), in both polar and nonpolar solvents, with special attention given to the variation of 谓_AH with the solvent鈥檚 dielectric constant 蔚. The theory involves a valence bond (VB) model for the complex鈥檚 electronic structure, quantization of the complex鈥檚 proton and H-bond motions, and a solvent coordinate accounting for nonequilibrium solvation. A general prediction is that 谓_AH decreases with increasing 蔚 largely due to increased solvent stabilization of the ionic VB structure A鈥?/sup>路路路HB+ relative to the neutral VB structure AH路路路B. Theoretical 谓_AH versus 1/蔚 slope expressions are derived; these differ for polar and nonpolar solvents and allow analysis of the solvent dependence of 谓_AH. The theory predicts that both polar and nonpolar slopes are determined by (i) a structure factor reflecting the complex鈥檚 size/geometry, (ii) the complex鈥檚 dipole moment in the ground vibrational state, and (iii) the dipole moment change in the transition, which especially reflects charge transfer and the solution phase proton potential shapes. The experimental proton frequency solvent dependence for several OH路路路O H-bonded complexes is successfully accounted for and analyzed with the theory.}