Light absorption by iodine vapour under conditions productive ofJoshi Effect

Abstract

The absorption spectrum of iodine was studied using a special design (due to Prof. Joshi) ozoniser which provided an absorbing column of about 46 cms. Iodine vapour in presence of an annular film of I2, KI and KI3 excited in the above ozoniser, due to potentials varied in the range 0·5 to 1·5 kV of 50 cycles frequency gave a negativeJoshi Effect corresponding to a current decrease in ordinary light of 50–60%. The Effect %Δi is maximum near the threshold potential, V m . The area of the surface exposed to the radiation is an important determinant of Δi. Under transverse irradiation Δi was much greater than under longitudinal one. The iodine glow near maximum Δi, was too feeble for spectroscopic record. Absorption spectra of unexcited iodine and for that under (transverse) irradiation at exciting potentials near maximumJoshi Effect were sensibly the same in respect of wavelength position of, and the intensity distribution amongst, the absorption bands. This applies to the iodine spectrum in Crookes’ tube discharge in dark and under ordinary and Hg-arc light. The main seat of the phenomenon may not be therefore in the bulk of the excited gas but in an adsorption-like boundary layer as postulated in Joshi’s Theory.