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 (Ã 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 Ã 1B2 state was shown to be clearly higher than for the ground X̃ 1A 1 state. Finally, the experimentally observed diminution of the splitting upon deuteration of the transferring hydrogen is also accounted for by our theoretical results. © 1995 American Institute of Physics.