Nondissociative electron capture by disulfide bonds

By means of Rydberg electron-transfer spectroscopy (RETS), negative ion photoelectron spectroscopy (NIPES), and quantum chemistry calculations, we have studied electron attachment properties of a series of saturated disulfides: 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 complexes. NIPES experiments provide vertical detachment energies for the three disulfide monomer anions along with their Franck-Condon profiles. Fitting these spectra, using model potentials for the S-S stretch coordinate, finds that the adiabatic electron affinities of these disulfides are positive but rather small, about 0.1 eV. These experimental data compare well with the results of ab initio calculations, performed-at the MP2 level with large basis sets.