Use of the extraordinary infrared transmission of metallic subwavelength arrays to study the catalyzed reaction of methanol to formaldehyde on copper oxide

Ordered arrays of subwavelength holes in thin metallic films have been produced that exhibit extraordinary transmission resonances throughout the infrared including the range of wavelengths that excite fundamental molecular vibrations. This phenomenon is attributed to the excitation of surface plasmons which propagate along the surface and tunnel through the holes without being scattered out of an incident beam. Commercial nickel mesh has been coated with copper to reduce the hole size enhancing surface plasmon lifetimes (narrowing resonances) and enabling the study of catalytic processes on the Cu surface. The copper oxide catalyzed reaction of methanol has been studied by recording enhanced zero-order FTIR transmission spectra of the copper mesh activated with a drop of water and then exposed to a drop of methanol. Transformation of CH3OH(ads) to CH3O(ads) and then to the product CH2O(ads) is observed at room temperature and in air with a very simple procedure. The spectrum of adsorbed formaldehyde is analyzed with regard to its orientation on the copper oxide surface.