A CASSCF/MRCI study of the low-lying Rydberg states of ClO

An ab initio calculation has been performed on the lowest seven doublet and six quartet Rydberg states of ClO at the CASSCF/MRCI level and with basis sets suitable for the extended molecular orbitals of such states (aug-cc-pVTZ with up to eleven extra Gaussian functions). Calculations on the quartet states reveal the energy ordering of Rydberg orbitals to be 4s sigma, 4p pi, 4p sigma, 3d delta, 3d sigma and 3d pi. The calculated doublet ab initio potential curves confirm experimental assignments of the C(2)Sigma(-) and F(2)Sigma(-) states but require reassignments for the symmetries of the D ((2)Delta), E ((II)-I-2) and H ((2)Delta) Rydberg states. These revisions are supported by spin-orbit coupling calculations that suggest the separation between the Omega components is small. In addition, a (2)Sigma(+) State has been identified as the likely upper state for two previously unassigned vibronic bands recorded in absorption studies.