An ab initio study of the low-lying electronic states of YO2 and franck-condon simulation of the first photodetachment band of YO 2-

A variety of density functional theory and ab initio methods, including B3LYP, B98, BP86, CASSCF, CASSCF/RS2, CASSCF/MRCI, BD, BD(T), and CCSD(T), with ECP basis sets of up to the quintuple-zeta quality for Y, have been employed to study the X̃2B2 state of YO2 and the X̃1A1 state of YO2-. Providing that the Y 4s24p6 outer-core electrons are included in the correlation treatment, the RCCSD(T) method gives the most consistent results and is concluded to be the most reliable and practical computational method for YO2 and YO2-. In addition, RCCSD(T) potential energy functions (PEFs) of the X̃2B2 state of YO 2 and the X̃1A1 state of YO 2- were computed, employing the ECP28MDF_aug-cc-pwCVTZ and aug-cc-pVTZ basis sets for Y and O, respectively. Franck-Condon factors, which include allowance for Duschinsky rotation and anharmonicity, were calculated using the computed RCCSD(T) PEFs and were used to simulate the first photodetachment band of YO2-. The simulated spectrum matches very well with the corresponding experimental 355 nm photodetachment spectrum of Wu, H.; Wang, L.-S. J. Phys. Chem. A 1998, 102, 9129, confirming the reliability of the RCCSD(T) PEFs used. Further calculations on low-lying electronic states of YO2 gave Te's and Tvert's of the Ã2A1, B̃2B1, and C̃2A2 states of YO2, as well as EAs and VDEs to these states from the X̃1A1 state of YO 2-. On the basis of the ab initio VDEs obtained in the present study, previous assignments of the second and third photodetachment bands of YO2- have been revised.