Nondissociative electron capture by disulfide bonds

By means of Rydberg electron-transfer spectroscopy (RETS), negative ion pho toelectron spectroscopy (NIPES), and quantum chemistry calculations, we hav e studied electron attachment properties of a series of saturated disulfide s: dimethyl disulfide, diethyl disulfide, and dipropyl disulfide. Both RETS and NIPES experiments show that the valence anions of these disulfides are stable. RETS further shows that these negative ions result from attachment of nonzero energy electrons (0.2 eV), in contrast to dimers and larger com plexes. NIPES experiments provide vertical detachment energies for the thre e disulfide monomer anions along with their Franck-Condon profiles. Fitting these spectra, using model potentials for the S-S stretch coordinate, find s that the adiabatic electron affinities of these disulfides are positive b ut rather small, about 0.1 eV. These experimental data compare well with th e results of ab initio calculations, performed-at the MP2 level with large basis sets.