A high-level ab initio theoretical study has been performed on the spectra and bond energies of pernitric acid, HO2NO2. Excellent agreement with experimental rotational constants, N-15 NMR chemical shifts, HO2 + NO2 reaction enthalpy, and vibrational frequencies are obtained. Slight revisions of low-frequency normal modes have been made. Vertical excitations are computed by CASPT2 for comparison with future high-resolution UV-visible spectra and match the low resolution UV-visible spectra of pernitric acid in solution. The optimized geometries reported are superior to previous microwave structures because assumptions of bond lengths and angles from the analogous nitric acid and hydrogen peroxide molecules introduce significant errors.