AB Initio HF SCF Calculation of the Effect of Protonation on Vibrational Spectra of Adenine
Vibrational spectroscopy represents a powerful tool for studying the proton transfer phenomena [1,2]. It is highly desirable to interpret the observed spectral changes, which might be caused by protonation, on the basis of theoretical calculations. Such calculations must include vibrational spectra of series differently protonated, and often relatively large biological molecules, and take the effect of environment, mostly aqueous solution, into account. As a best suited for this purpose seems to be a combination of a low-cost ab initio HF SCF method, able to handle molecules up to 25 atoms, and normal coordinate calculation where the SCF force field is fitted by means of a few scaling factors to the observed frequencies. The resulting scaling factors implicitly involve the effects of electron correlation, weak intermolecular interactions, incompleteness of basis set, and anharmonicity. The transferability of scale factors among related molecules has been shown to be a good approximation [3,4].
KeywordsVibrational Spectrum Vibrational Spectroscopy Potential Energy Distribution Weak Intermolecular Interaction Stretch Force Constant
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