The valence and Rydberg excited states of CH2: A theoretical exploration

Using the completed active space second-order perturbation (CASPT2) method, valence and Rydberg excited states of CH2 molecule are probed with the large atomic natural orbital (ANO-L) basis set. Five states are optimized and the geometric parameters are in good agreement with the available data in literatures, furthermore, the state of 21B1 is obtained for the first time. Valence and Rydberg excited states of CH2 are also calculated for the vertical transitions with the ANO-L+ basis set that is constructed by adding a set of 1s1p1d Rydberg orbitals into the ANO-L basis set. Two Rydberg states of the p3A2 and r3B1 at 9.88 and 10.50 eV are obtained for the first time, and the 3a1 ? 3dyz nature of the state p3A2 and the 3a1 ? dx2-y2 nature of the state r3B1 are confirmed. (c) 2012 Wiley Periodicals, Inc.