Ab initio study of the photochemistry of aminopyrimidine

Complete active space self‐consistent field (CASSCF), multi‐reference configuration interaction calculations (MR‐CISD), and equation of motion coupled‐cluster with singles and doubles (EOM‐CCSD) calculations are presented in order to elucidate the photodeactivation pathways of 6‐aminopyrimidine after vertical excitation to the S₁ ¹nπ* state. Vertical excitation energies are reported up to the S₇ state. Two S₁ excited state minima, both of ¹nπ* character, and three strongly puckered ¹ππ* minima on the crossing seam (MXS) between the S₀ and the S₁ potential energy surface were found. Nonadiabatic reaction paths are discussed by linearly interpolating between the two minima and all MXS, which explain and extend observations made in recent surface‐hopping dynamics CASSCF investigations [Barbatti and Lischka, J Phys Chem A 2007, 111, 2852]. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008