Bidimensional tunneling splitting in the à 1B2 and X̃ 1A1 states of tropolone

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Abstract
The intramolecular proton transfer in tropolone has been theoretically analyzed. Ab initio calculations using a variety of basis sets have been performed for both the singlet ground state (X̃ 1A1) and the first excited singlet state (à 1B2). A configuration interaction all single excitation method (CIS) has been used to deal with the excited singlet state. Tunneling splittings in both electronic states have been obtained by fitting a bidimensional surface into the ab initio results. This way, a new strategy designed to avoid calculations of the intrinsic reaction coordinate (IRC), which require a very long computer time, is proposed and shown to give accurate results. Our calculations provide a theoretical interpretation of previous extensive spectroscopical data from which the tunneling splitting for the excited à 1B2 state was shown to be clearly higher than for the ground X̃ 1A1 state. Finally, the experimentally observed diminution of the splitting upon deuteration of the transferring hydrogen is also accounted for by our theoretical results.