An ab initio study of the low-lying electronic states of YO2 and Franck-Condon simulation of the first photodetachment band of YO2-

A variety of density functional theory and ab initio methods, including B3LYP, 1398, 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 (X) over tilde B-2(2) state of YO2 and the (X) over tilde (1)A(1) state of YO2-. Providing that the Y 4s(2)4p(6) 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 (X) over tilde B-2(2) state of YO2 and the (X) over tilde (1)A(1) state of YO2- 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 T-e's and T-vert's of the (A) over tilde (2)A(1), (B) over tilde B-2(1), and (C) over tilde (2)A(2) states of YO2, as well as EAs and VDEs to these states from the (X) over tilde (1)A(1) state of YO2-. 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.