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

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 X̃B state of YO and the X̃A state of YO. Providing that the Y 4s4p 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 YO and YO. In addition, RCCSD(T) potential energy functions (PEFs) of the X̃B state of YO and the X̃A state of YO 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 YO. 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 YO gave T's and T's of the ÃA, B̃B, and C̃A states of YO, as well as EAs and VDEs to these states from the X̃A state of YO . On the basis of the ab initio VDEs obtained in the present study, previous assignments of the second and third photodetachment bands of YO have been revised. © 2008 American Chemical Society.