Photoreactions of small molecules at the surface of alkali metal halides

Photophysical Processes Related to Photoadsorption and Photocatalysis on Wide Band Gap Solids: A Review

“…06 more active than narrow band gap oxides in respect to the photolysis of adsorbed water [36] (see, also [37]). Similar, in the studies of a series of alkali halides the photoadsorption of O 2 and CO 2 , the photodecomposition of CO 2 and H 2 O and the photooxidation of H 2 and CO at repeated irradiation of adsorbents (except of iodides) with oxygen preliminary photoadsorbed have been observed (see [38] and references there). It has been established that the red limits of water and CO 2 photolysis are close to 5 eV, while the red limits of oxygen photoadsorption are considerably shifted (E red ≈ 3.0 ÷ 4.0 eV) to the red compared with the alkali halides bulk exciton absorption bands (5 ÷ 10 eV).…”

“…If the latter is the case, adsorbed water molecule seems to be able to "choose itself" the appropriate excited state from the wide variety of exciton-like states which exist in the dispersed wide band gap solids. The surface reactions observed in alkali halides under irradiation in the bulk exciton absorption bands (hν 1 , Figure 3) are in many respects similar to those photostimulated below the exciton band (hν 2 , Figure 3) [38,39,[58][59][60]. For distinctness, KBr will be discussed below.…”

“…The alkali halides occurred to be convenient adsorbents for demonstration and for studies [15,38,39] of the so called photostimulated postsorption (PSPS) of small molecules (hν 3 region, path 1-2-10-3-4-5, Figure 3). The exciton decay onto Frenkel defects in alkali halides (eqs.…”

“…Activation energy estimate E a = (0.135 ± 0.01) eV is in a good agreement with the energy gap between the relaxed 2p-state of F-center and the bottom of the conduction band in KBr. In contrast with the rates of PSPS O 2 induced in the F band of F center, those for L bands only slightly depend on temperature [15,38]. The PSPS of acceptor molecules have been also observed on KI, RbI [38,58] and on X-rays irradiated CaF 2 and BaF 2 [64].…”

“…In contrast with the rates of PSPS O 2 induced in the F band of F center, those for L bands only slightly depend on temperature [15,38]. The PSPS of acceptor molecules have been also observed on KI, RbI [38,58] and on X-rays irradiated CaF 2 and BaF 2 [64]. The thermally stimulated post-sorption (TSPS) of small molecules on oxides and alkali halides have been discussed elsewhere [13,38,45].…”