Photoelectron spectroscopy of free radicals: 4-methyl-sulfonyloxy-TEMPO.

HeI and HeII photoelectron spectra of persistent free radical: 2,2,6,6-tetramethyl-4-(methylsulfonyloxy)piperidinyl-1-oxide (CH3SO3-TEMPO) have been measured. The analysis of the electronic structure is based on comparison with the spectra of related radicals and with DFT calculations. The electronic structure of the nitroxide group in the title radical seems unaffected by the presence of substituent group. This is consistent with results observed for other nitroxide radicals and with the electrochemical oxidation potentials.