Theoretical study of the first electronic state of the FCO2 radical

Following the successful results for the ground electronic state vibrational levels of the FCO2 radical, the same theoretical approach has been used for predictions of the vibrational levels of the first electronic excited state A (2)A2. This excited electronic state interacts vibronically with the fourth electronic excited state C (2)B1 by normal vibrational modes ν5 and ν6. The intrastate and interstate coupling constants have been determined within the adiabatic quadratic approach in the framework of the Köppler, Domcke, and Cederbaum model Hamiltonian. All ab initio calculations (optimization, potential energies, first and second derivatives) have been performed in two high-level methods (EOMIP-CCSD and UHF-CCSD(T)) using the CFOUR program package. The analytically determined vibronic constant for the ν5 mode has a value of 4061 cm(-1). This causes weak vibronic coupling, implying only the flattening of the potential energy curve, which is in contrast to a double-minimum for the ground electronic state.