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Comment On: The Relation Between Intensity and Dipole Moment for Bending Modes in Linear Molecules

Gwaltney, S. R., & Bartlett, R. J. (1993). Comment On: The Relation Between Intensity and Dipole Moment for Bending Modes in Linear Molecules. Journal of Chemical Physics. 99, 3151-3152.

Abstract

In a recent paper [J. Chem. Phys. 97, 4616 (1992)] that examines the relationship between experimental and computed intensities for bending modes of linear molecules, Sørensen and Jørgensen state that ‘‘most recent quantum mechanical computations predict band intensities of the bending modes in linear molecules that are approximately a factor of 2 bigger than observed intensities, and it is shown that the problem relates to the ab initio treatment.’’ It is further stated that ‘‘the disturbingly big discrepancies...are real, and the cause of the discrepancies has to be sought in the ab initio computation of the dipole moment.’’ This apparent failing of theory is addressed here by demonstrating that coupled‐cluster calculations provide intensities for the bending modes of acetylene, carbon dioxide and nitrous oxide, of 177, 55, and 8 km/mol which compare favorably with the experimental values of 177, 55, and 7; while that for HCN is 70 compared to an experimental value of 58. The discrepancy in the latter might recommend some reconsideration of the experimental value, including the role of electrical and mechanical anharmonicity.