Electronic Spectra, Excited-State Geometries, and Molecular Electrostatic Potentials of Hypoxanthine: A Theoretical Investigation

Abstract

The ground-state geometry of hypoxanthine was optimized at the MP2, B3LYP, and HF levels by employing the 6-311++G(d,p) basis set. The vertical singlet transition energies were calculated at the CASSCF/ 6-31+G(d), TD-B3LYP/6-311++G(d,p), and CIS/6-311++G(d,p) levels by using the MP2-, B3LYP-, and Hartree−Fock-optimized geometries, respectively. In the case of the CASSCF calculations, the active space consisted of the 2σ, 6π, and 4π* orbitals. The σ orbitals were used to compute the nπ* transitions. The effects of dynamic correlation on the CASSCF energies were considered at the second-order multiconfigurational quasi-degenerate perturbation (MCQDPT2) theory. The effect of hydration was considered by including three water molecules in the first solvation shell of hypoxanthine. The geometry of the molecule was also optimized in the lowest singlet ππ* and nπ* excited states at the CIS/6-311++G(d,p) level. The characteristics of the ground and excited-state potential energy surfaces were ascertained from a ha...