Density functional theory with the combined Becke's three-parameter exchange functional in combination with the Lee, Yang, and Parr correlation functional (B3LYP) exchange-correlation energy functions using the 6-31G * basis set was applied to study the structures and vibrational infrared (IR) spectra of 9-methyladenine and the related compounds purine and adenine. The calculated force fields were scaled with the scale factors determined from purine. The predicted vibrational frequencies and isotopic shifts of IR bands of adenine and 9-methyladenine were compared with the available observed matrix-isolated IR spectra with a mean deviation of about 6.4 cm −1 . The results made it possible to give reliable assignments of the IR spectra of these molecules. This study shows that the scaled density functional force field approach enables, through the transferability of scale factors, good interpretation of vibrational spectra of large molecules.

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The electronic structure of the Keggin anion ( P W ,~O~U )~-has been calculated by the DV-Xa method. The nature of the chemical bonds of the Keggin anion and the relationship between electronic structure and catalytic behavior are discussed. At the same time, the difference in electronic structure and the relationship in catalytic behavior between (PW12040)~-and (PMo,zO,)'-are compared.

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