Surface-Enhanced Infrared Absorption Spectroscopy of p-Nitrothiophenol on Vapor-Deposited Platinum Films

Abstract

Surface-enhanced infrared absorption (SEIRA) has been observed by transmission spectroscopy on a vapor-deposited platinum substrate. Monolayers of p-nitrothiophenol ( p-NTP) adsorbed on thin island films of platinum were used to probe the enhancement and distortion of the absorption bands of p-NTP. The greatest enhancement was accompanied by distortion of the strongest band in the spectrum of p-NTP into a bipolar shape. The magnitude of enhancement was dependent on the size of the metal islands and their proximity to each other. The applicability of the surface selection rule to SEIRA was confirmed by the weakness of the antisymmetric NO₂ stretching band in the spectra of the self-assembled monolayers. Although these preliminary transmission studies show only modest (∼10×) enhancement when p-NTP is vapor-deposited onto platinum films, the potential of SEIRA for transmission studies on platinum island films has been established.