Photoelectron spectroscopy of so₃^- at 355 and 266 nm

Photoelectron spectra of SO₃^- were recorded at 266 and 355 nm to study photodetachment of the SO₃^- anion (²A₁) to the ground state of neutral SO₃^- (¹A′₁). A long vibrational progression in the 355 nm spectrum is attributed to excitation of the umbrella mode, v₂, consistent with predictions that C_3v symmetry SO₃^- yields D_3h symmetry SO₃ upon photodetachment. At 266 nm, photodissociation of SO₃^- to SO₂ + O^- was also observed. The geometry and normal-mode frequencies of SOi~ and SO) as well as the adiabatic electron affinity (AEA) and vertical detachment energy (VDE) of SO₃^- have also been calculated with ab initio (MP2 and CCSD(T)) and DFT methods. Using theoretical predictions and experimental data, Franck-Condon simulations of the photoelectron spectra were found to be in good agreement with experiment. The calculated AEA agreed well with experiment, but the VDE was found to be less accurate, presumably because of the large geometry change between anion and neutral.