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.

Dark and photoconductivities in methylbixin have been studied as a function of applied field and temperature. The results suggest that a single discrete trapping level is involved in charge carrier generation and the dominant trapping level is different for dark and photoconduction. Space charge limited current theory has been used to evaluate various transport parameters. The effective drift mobility is shown to be field dependent.