Predicting physical properties of peroxynitrite by quantum mechanics

In summary, quantum chemical calculations have been useful in verification of the proper identification of ONOO^- in solution and as matrix isolated salts through NMR, Raman, IR, and UV-visible spectroscopies, and through computed relative energies. Some rules in using quantum mechanical calculations on molecules are as follows: (1) use a basis set with at least two functions per valence orbital and polarization d functions on each heavy atom; (2) SCF bond distances are usually too short by ~10 pm and correlated bond lengths are slightly longer than SCF bond lengths; (3) SCF harmonic vibrational frequencies are usually ~10% higher than observed fundamental bands, correlated methods predict frequencies that are lower than SCF but still about 5% above the fundamentals; and (4) systematically improve the levels of theory until the property is predicted consistently to the desired accuracy.