APPLICATION OF POLARIZATION MODULATION FOURIER-TRANSFORM INFRARED-SPECTROSCOPY FOR THE IN-SITU STUDY OF SPONTANEOUSLY ADSORBED MONOLAYERS

Polarization modulation Fourier transform infrared reflection absorpti on spectroscopy (PM-FTIRRAS) has been applied to study the structure o f gold surfaces modified with organic monolayers by spontaneous adsorp tion. It is found that the infrared spectrum of a hydrophobic octadeca nethiol monolayer changes little from the ''situ spectrum when placed in the presence of deuterium oxide solution. The changes that are obse rved in the infrared spectrum are characteristic of rotations about th e terminal methyl group, consistent with organic monolayers in contact with aqueous solutions. In the presence of acetonitrile solutions, th e in situ spectrum contains few changes beyond those observed in the a queous solutions, but nothing that indicates a dramatic alteration of the monolayer structure. A slight peak shift to higher wavenumber and additional peak asymmetry for the asymmetric methylene stretch in the presence of acetonitrile may indicate some amount of hydration of the outer portions of the monolayer not observed in the aqueous solutions. This infrared data is consistent with previous spectroscopic observat ions but deviates from electrochemical measurements made with these mo nolayer surfaces.