Franck–Condon profiles for the X2B1 ← X1A1 band of the anion photoelectron spectroscopy of OIO based on discrete variable representation

The three-dimensional potential energy surfaces around the equilibrium geometries of OIO‾(X¹A₁) and OIO(X²B₁) were calculated with two double hybrid density functionals XYGJ-OS and XDH-PBE0 and three hybrid density functionals B3LYP, MPW1PBE and B97–3 in conjunction with various basis sets. The potential energy surfaces were used in calculations of anharmonic vibrational wavefunctions of OIO‾(X¹A₁) and OIO(X²B₁) by virtue of discrete variable representation. Therefrom, the vibrational frequencies including anharmonicity of both states were obtained, and the Franck-Condon factors between these two states were calculated including allowance for anharmonicity and Duschinsky effect. The X²B₁ ← X¹A₁ band of the anion photoelectron spectroscopy of OIO was then simulated using the computed Franck-Condon factors broadened with a Gaussian line shape. Based on the theoretical Franck-Condon factors, a more detailed assignment of the observed vibrational structure of the photoelectron spectrum, which includes the photodetachment from vibrational excited states of OIO‾(X¹A₁) has been proposed. Comparison between the simulated and experimental spectra by iterative Franck-Condon analysis procedure has been made, the equilibrium geometrical parameters for OIO anion have been derived to be r(OI)= 1.8508 ± 0.0003 Å and θ(OIO)= 107.9 ± 0.3º.