Pavel S. Mozhaev

An ESR and Optical Spectroscopic Study of the Mechanism of Photostimulated Reactions in Hydrogen Cyanide γ-Irradiated at 77 K

Changes in the electronic absorption spectra and ESR spectra in the course of photobleaching of radiolyzed solid HCN with light of different wavelengths (236–600 nm) were studied by ESR and optical spectroscopy. Two bands at 270 and 290 nm in the optical spectrum were attributed to the presence of H2C=N⋅ and HC⋅=NH radicals, respectively (the molar absorption coefficients are k270≈ 2.7 × 102l mol–1cm–1and k290≈ 1.5 × 102l mol–1cm–1, respectively). Structureless broad bands with maximums at 313 and 465 nm, which were detected after the exposure of a sample to light with λ ≥ 300 nm, can belong to the cyanide ions (CN–) and H2C=N+cations (the molar absorption coefficients of the ions are kion= (0.4–1.0) × 102l mol–1cm–1). In the photobleaching of γ-irradiated HCN (λ = 236–280 nm), H2C=N+radicals were additionally formed by the photoinduced reaction of electron transfer from the CN–anion to the H2C=N+cation. The amount of these radicals generated in the course of photobleaching is several times greater than that of the same radicals formed in the radiolysis via hydrogen atom addition to the multiple bond of HCN molecules.

Radiation-Induced Cryopolymerization of Epichlorohydrin

The polymerization of epichlorohydrin occurs in the temperature region of glass transition as a result of heating of the samples preirradiated at 77 K. The specific heat of polymerization of epichlorohydrin ΔHwas determined to be 95.4 ± 6.0 kJ/mol. The postirradiation polymerization proceeds through the cationic mechanism. The chain propagation rate constant was estimated at kp= 10–18 exp(–14200/RT) cm3/s for the temperature range 95–140 K. The dynamics of postirradiation polymerization of crystalline epichlorohydrin is substantially different from the polymerization dynamics of the glassy monomer. The polymer yields were found to be 3 and 12% for the crystalline and the glassy monomer, respectively. Heating of an irradiated glassy solution of hydrogen cyanide in epichlorohydrin results in the formation of the corresponding copolymer.

Photosensitivity of paramagnetic centers in radiolyzed solid hydrogen cyanide

The photolysis of solid hydrogen cyanide and the effects of UV light on60Co-γ-irradiated HCN at 77 K were studied using an ESR technique. As in the case of radiolysis, the HZ2C=N radical formed due to “sticking” of the H atom to the triple bond of the HCN molecule is the main radical product of low-temperature HCN photolysis. The C=N− radicals are accumulated at 77 K in insignificant amounts (≈3 %). It was established that radical and ionic products stabilized in y-irradiated HCN possess photochromism and under the action of UV light enter photochemical reactions leading to their decomposition. Upon photobleaching, the concentration of H2C=N− radicals first increases two- to threefold because of the decomposition of H2C=N− ions and then decreases. The presence of radicals and ions formed upon the low-temperature radiolysis of HCN broadens the optical absorption band of the system, and the boundary of the action spectrum shifts from 280 nm (for nonirradiated HCN) to the visible region at 400–440 nm.