Collect. Czech. Chem. Commun. 2003, 68, 447-462

MR-CISD and MR-AQCC Calculation of Excited States of Malonaldehyde: Geometry Optimizations Using Analytical Energy Gradient Methods and a Systematic Investigation of Reference Configuration Sets

Silmar A. do Montea,*, Michal Dallosa, Thomas Müllerb and Hans Lischkaa,*

a Institute for Theoretical Chemistry and Structural Biology, University of Vienna, Währingerstrasse 17, A-1090, Austria
b Central Institute for Applied Mathematics, Research Centre Juelich, D-52425 Juelich, Germany


Extended MR-CISD and MR-AQCC calculations have been performed on the ground state and the first two excited states of malonaldehyde. Full geometry optimizations have been carried for Cs and C2v structures both at MR-CISD and MR-AQCC levels. Vertical and minimum-to-minimum excitation energies and oscillator strengths have been computed. Systematic studies have been undertaken concerning several types of reference spaces. Agreement with the experimental 0-0 transition energy to the S1 state (expt. 3.50 eV, calc. 3.56 eV) and for the vertical excitation to S2 (expt. band maximum 4.71 eV, best estimate 4.86 eV) is very good. In agreement with the CASSCF/CASPT2 results by Sobolewski and Domcke (J. Phys. Chem. A 1999, 103, 4494), we find that the hydrogen bond in malonaldehyde is weakened by excitation to the S1 state. The barrier for proton transfer in the S1 state is increased in comparison with the ground state.

Keywords: Excited states; Multireference configuration interaction; Proton transfer; Hydrogen bond; Malonaldehyde; Ab initio calculations.

References: 36 live references.