The charge transfer mechanism in the SERS of 2-methylpyrazine on silver electrode

SERS spectra of 2-methylpyrazine have been recorded on silver electrode in a range of potential from 0.00 to -0.75 V vs. a saturated Ag/AgCl/KCl reference electrode. The so obtained spectra have been compared with the Raman of the aqueous solution and the observed differences between the relative intensities of Raman and SERS spectra have been interpreted on the bash; of a charge transfer mechanism. The most enhanced bands correspond to modes that relate the equilibrium geometries of the neutral molecules and its anion radical, while the behaviour of other less enhanced bands is due to vibronic coupling between the ground state of the anion radical and other of its possible excited states, in order to check this enhancement mechanism, we have used the theoretical results provided by ab initio calculations on the neutral molecule and its anion radical. (C) 1999 Elsevier Science B.V. All rights reserved.