Correlation between intramolecular bond distances and stretching vibrations for polar molecules: An ab initio study

Abstract

ABSTRACT:The correlation between intramolecular bond length and vibrational Ž . frequency shifts was calculated at the MP4 aug-cc-PVTZ ab initio level for a number of Ž y y . molecules LiH, BH, HF, OH , HDO, BF, CN , and HCl exposed to uniform electric fields in the range from y0.10 to q0.10 au. The '' vs. r '' correlation curves always e consist of two branches, each approximately linear. The slopes for the molecules y1i nvestigated here vary between y2500 and y16600 cm rA. The slopes are well described by an expression containing only the free-molecule second-and third-order force constants and the reduced mass for the stretching mode. Experimental data for polar molecules can be expected to show deviations from a linear '' vs. r '' correlation e Ž .i for molecules where the maximum of the frequency vs. field curve occurs at a positive Ž . field and ii for molecules where the maximum of the frequency vs. field curve falls on Ž . the negative-field side but very close to the zero-field case, and iii in bonding situations when there is much electron overlap. As opposed to uniform-field situations, anharmonicity and electronic overlap have a substantial influence on the ''frequency vs. r '' slopes in molecular environments.

H‐bond and electric field correlations for water in highly hydrated crystals

“…We notice that the least-squares-fitted line does not pass through the gas-phase point, for which we have no good explanation. A detailed account of the 'm(OH) versus r e (OH)' correlation and nonlinearities of this curve were investigated by Hermansson and Probst [72] for a series of polar molecules in electric fields, calculated at the MP4/aug-cc-pVTZ electronic level and the harmonic vibrational level.…”