Excited State Energetics and Proton Transfer Barriers in Malonaldehyde
Journal of Physical Chemistry
American Chemical Society
The ground and first four excited electronic states of malonaldehyde are examined by ab initio methods, using a variety of basis sets including 4-31G, 6-311G**, and 6-31+G**. The lowest-energy excited state is found to be ~T-T*, followed in order by 3n-~*, In**, and IT-*. At the CIS level, the proton-transfer barriers in the excited states are all higher than the ground-state barrier; the exception is IT-* for which the barrier is lower. An inverse correlation is noted between the height of each barrier and the strength of the intramolecular H bond. Correlation, when added via second-order Maller-Plesset perturbation theory, reduces the excitation energy of each state. As is typical of the ground state, electron correlation lowers the proton-transfer barrier in the excited states as well. Their correlated barriers are all smaller than that in the ground state. Indeed, in a number of excited states, the transfer potential is likely to contain only a single symmetric minimum.
Excited State Energetics and Proton Transfer Barriers in Malonaldehyde K. Luth, S. Scheiner J. Phys. Chem. 1994 98, 3582-3587.