Spectroscopic characterization of the first excited state and photochemistry of the HO3 radical

We report the one-dimensional cuts of the six-dimensional potential energy surfaces (PESs) of the ground and lowest doublet and quartet electronic states of trans-HO3 at the MRCI-F12/aug-cc-pVTZ level of theory. Theoretical calculations predict that the first excited state (A(2)A) presents a real minimum on its PES and possesses a nonplanar structure. The adiabatic excitation energy at the MRCI+Q and MRCI-F12 levels shows that the A(2)A state lies in the near-infrared region. Both the transition dipole moment and the oscillator strength were predicted to be weak, which suggests that photodissociation of HO3 to produce OH and O-2 after UV-Vis absorption is not a plausible mechanism. The harmonic vibrational frequencies and rotational constants of the weakly bound complex OH-O-2 in the two electronic states were predicted to help in its detection. Our PES shows that the reactions of H + O-3 or HO2 + O in their ground states do not lead to trans-HO3 in its ground electronic state if one of the component fragments, i.e., HO2(A(2)A ') + O(P-3) or H(S-2) + O-3(B-3(2)), is excited.