Absorption spectra of molecules adsorbed within porous media and the effect of molecular orientation

Abstract

The problem of optical absorption due to oriented molecular films adsorbed within porous media has been treated theoretically in the approximation that the adsorbent behaves as a collection of spherical particles or cavities of small size compared with the wavelength of light. Expressions for the contribution to the spectrum arising from optical modes involving charge displacement parallel to the local substrate surface, relative to those involving normal displacements, are derived from which a number of conclusions are reached. Thus for example it is shown that in general the relative intensities of different absorption bands are dependent upon the detailed geometry of the porous adsorbent. The equations presented offer the first opportunity for quantitative interpretation of infra-red absorption spectra for porous adsorbent-adsorbate systems.