Photo- and Thermochemical Reactions in Potassium Chloride Crystals— A Quantitative Study of the M Centre—

Abstract

By experiments upon the thermal stability of the M, R and N centres in KCl crystal coloured additively, it was revealed that R₁ and R₂ centres dissociated thermally into F, M and N centres above 50°C, N centres dissociate into F and M centres above 100°C and M centres dissociated into F centres above 130°C. The relaxation time τ for the dissociation process of the M centre is expressed by 1⁄τ=2·10¹²×exp (−1.31⁄kT) sec⁻¹ for kT in ev. The corresponding experiment on the R centre was unsuccessful. With use of the above properties of photochemical products, the number of the F centre corresponded to one M centre was determined with high precision. In addition to this, the quantum yield of the M centre in the photochemical reaction with M band light was investigated as a function of temperature. Combining these two experiments with a quantitative analysis of dichroism both in the F and M bands, it is concluded that the M centre is one-electron centre, that the 2nd M band exists in the F band region, that the absorption considered to be a continuum of the M centre exists in the short wavelength branch of the F band and that the oscillator strength of the M main band is assigned to 0.83. The reciprocal of the quantum yield of the M centre is expressed by 1+1.4·10⁻⁷ exp (0.50/kT) for kT in ev. It is also concluded that the R centre has its another absorption in the spectral region of the F band.