Reaction Chemistry of Solid-State Pyridine Thin Films with Vapor Deposited Ag, Mg, and Al

Abstract

The reaction of pyridine in thin solid-state films with post-deposited Ag, Mg, and Al is investigated using surface Raman spectroscopy in ultrahigh vacuum. Vapor-deposited Ag forms metallic nanoparticles on the pyridine film, resulting in surface enhancement of the Raman scattering (SERS), with no reaction chemistry evident. Mg and Al react with pyridine by electron transfer to form radical anion intermediates, some of which are stabilized by entrapment in the solid pyridine matrix. With Mg, slight SERS enhancement is observed along with Mg-to-pyridine electron transfer to form pyridyl radical anions, some of which dimerize to 4,4′-bipyridine with loss of MgH2 and a neutral Mg atom. With Al, the reaction chemistry is initiated by a similar Al-to-pyridine electron transfer, but the radical anions so formed undergo further degradation to amorphous carbon. In total, these results demonstrate the complex reaction chemistry that can occur between heterocycles in the solid state and low work function metal atoms.