The change in semiconductive properties of vitamin A (alcohol and acetate) after adsorption of various vapours on its crystallite surface has been studied at a constant sample temperature. A rapid enhancement in the semi-conductivity has been observed. The rise in conductivity has been found to be exponential with increasing vapour pressure of the adsorbed gas. It has been suggested that charge transfer (CT) interaction may be responsible for such conductivity change. The adsorption process being efficiently reversible this CT complex is weakly bound.

The biological implication of these observations is discussed.

The change in semiconductive properties of β-apo-8′-carotenal, astacene and methyl bixin on adsorption of various vapours on the crystallite surfaces has been studied at a constant sample temperature. The adsorption of vapours enhances the semiconductivity of the polyenes appreciably. This enhancement depends on the chemical nature and also on the pressure of the adsorbed vapour. The adsorption and desorption kinetics follow the modified Roginsky-Zeldovich relation. A two stage desorption process, the first stage of which gives a Lennard-Jones potential energy curve and is followed by a rate-determining transition over a potential energy barrier to the second stage of adsorption forming weakly bound complexes between the vapour molecules and the polyene crystallites, can explain satisfactorily the experimentally observed kinetic data.

Adsorption and desorption ofn-hexane, cyclohexane, CCl₄, C₆H₆ ethylacetate, methanol and ethanol vapours on the crystallite surfaces of 2-nitrofluorene and three isomeric nitrobenzoic acid semiconductors have been investigated using electrical conductivity as a probe. Kinetic analysis data show that in all these vapour-semiconductor systems, the adsorption is a two-stage process. Existence of any relationship between the adsorption process and the compensation effect in dark conduction process has been examined. The compensation effect is generally observed in cases where the change in semiconduction activation energy is caused by a two-stage adsorption process.

On adsorption of various vapours, the electrical conductivity of nitroaromatic semiconductors 9-nitroanthracene, 1,4-dinitronaphthalene and 1,3,5-trinitrobenzene changes appreciably. This phenomenon has been used as a probe to study the adsorption and desorption processes in these nitroaromatic polycrystals. The adsorption and desorption kinetics have been found to follow the modified Roginsky-Zeldovich relation. Two adsorption processes have been identified. One, a two-stage process, the first of which gives a Lennard-Jones potential energy curve and is followed by a rate-determining transition over a potential energy barrier to the second stage of adsorption forming weakly bound complexes between the vapour molecules and the nitroaromatic crystallites. In the second process, in addition to the two stages of the first process, a third stage with a comparatively deep potential energy surface is reached by activation over a second potential barrier and strongly bound complexes are finally formed.