Potential-energy function for intramolecular proton transfer in the malonaldehyde cation

The reaction path and the corresponding energy profile for intramolecular hydrogen transfer in the ground state of the malonaldehyde cation have been characterized employing the UHF/MP2, CASSCF and CASPT2 methods. It is found that the malonaldehyde cation represents the interesting case of a very low-barrier intramolecular hydrogen bond. The relevance of these findings for the infrared spectroscopy of cations of intramolecularly hydrogen-bonded π-systems and for femtosecond time-resolved photoelectron spectroscopy of the exited-state dynamics of these systems are briefly discussed.