An ab initio study of the radical OH(X~2Π,A~2Σ~+)

The ground state X 2Π and excited state A 2Σ + of OH molecule have been studied using ab initio method. At the theoretical level QCISD( T )/6-311++G( 3df,3pd) , the calculated bond length of the ground state is 0.097 04 nm. For the excited state, the calculated bond legnth obtained by CASSCF at the large radical basis set is 0.100 98 nm. The calculated vertically excited energy from excited state A 2Σ +(ν=0) to ground state X 2Π(ν=0) is 4.469 2 eV. All our calculated theoretical results are in good agreement with the experimental values 0.09 706 nm, 0.101 21 nm and 4.398 0 eV respectively.