Ab initio calculations have been carried out on low-lying singlet and triplet states of TeO2 at different levels of theory with basis sets of up to the augmented-polarized valence-quintuple-zeta quality. Equilibrium geometrical parameters, harmonic vibrational frequencies, and relative electronic energies of the (X) over tilde (1)A(1), B-1(1), B-1(2), (1)A(2), (3)A(1), B-3(1), B-3(2), and (3)A(2) states of TeO2 have been calculated. Potential energy functions (PEFs) of the (X) over tilde (1)A(1) and the (1)B-1(2) states were computed at the complete-active-space self-consistent-field multireference configuration interaction level, with a basis set of augmented-polarized valence-quadruple-zeta quality. Franck-Condon factors (FCFs) for the electronic transition between the (X) over tilde (1)A(1) and (1)B-1(2) states of TeO2 were calculated with the above-mentioned ab initio PEFs. The (1)B-1(2)<--(X) over tilde (1)A(1) absorption spectrum of TeO2 was simulated employing the computed FCFs, which include Duschinsky rotation and anharmonicity, and compared with the recently published laser-induced fluorescence (LIF) spectrum of Hullah and Brown [J. Mol. Spectrosc. 200, 261 (2000)]. The ab initio results and spectral simulation reported here confirm the upper electronic state involved in the LIF spectrum to be the (1)B-1(2) state of TeO2 and also confirm the vibrational assignments of Hullah and Brown. However, our simulated spectrum suggests that the reported LIF spectrum from 345 to 406 nm represents only a portion of the full (1)B-1(2)<--(X) over tilde (1)A(1) absorption spectrum of TeO2, which extends from ca. 406 to 300 nm. Another dye other than the two used by Hullah and Brown is required to cover the 345-300 nm region of the LIF band. Ab initio calculations show strong configuration mixing of the (1)B-1(2) electronic surface with higher B-1(2) states in a region of large TeO bond length (greater than or equal to2.0 Angstrom) and OTeO bond angle (greater than or equal to135.0degrees)
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