Inner-shell excitation spectroscopy of peroxides

O 1s inner-shell excitation spectra of a number of vapor phase molecules containing peroxide bonds – hydrogen peroxide (H2O2), di-t-butylperoxide (tBuOtBu), benzoyl peroxide, ((C6H5(CO)O)2), luperox-F [1,3(4)-bis(tertbutylperoxyisopropyl) benzene], and analogous, non-peroxide compounds – water, t-butanol and benzoic acid have been measured. C 1s spectra are also reported. O 1s spectra of solid benzoic acid, di-t-butylperoxide and luperox-F recorded using a scanning transmission X-ray microscope, are also reported, and compared to the corresponding gaseous spectra. Spectral interpretation was aided by comparing the spectra of the peroxide and non-peroxide counterparts and with ab initio calculations. A characteristic O 1s→σ∗O–O transition at 533.0(3)eV is identified in each peroxide species, which is absent in the corresponding non-peroxide counterpart species. The energy and intensity of the 533eV peroxide feature is stable and thus useful for analysis of peroxides in mixtures, such as tracking residual peroxide initiators, or peroxides produced in fuel cells.