Separation of bulk and surface light absorption with an open photoacoustic cell

Abstract

A spectroscopic method for the study of adsorption of molecules onto a solid is demonstrated. It is shown in particular how the spectra of molecules adsorbed onto a solid surface and molecules in a solution outside the surface can be recorded simultaneously. The method is based on the information present in the phase of a photoacoustic signal. The experiments made to demonstrate this method were performed with an open photoacoustic cell. In this cell the temperature oscillations in the sample are transferred to a window. The thermal expansions of the window are detected by a piezoelectric crystal. Light absorbing molecules on the surface of the window and in the bulk liquid give signals with different phases that can be separated by phase sensitive detection.