The radiation chemistry of low temperature methanolic glasses

Abstract

A study has been made of the visible, u.v. and e.s.r. spectra produced when glassy methanol at 77 °K is irradiated with cobalt-60 y-rays and of the effects on these of: (i) various additives including 2-methyl-pent-1-ene, sodium hydroxide, sulphuric acid, carbon tetrachloride, benzyl chloride, ferric chloride and naphthalene; (ii) subsequent illumination with either u.v. light or visible light (546 and 578 nm); and (iii) subsequent warming. The data are consistent with a mechanism the major features of which are CH 3 OH gl —vw-> e t - + CH 3 OH (-> CH 3 OH 2 + . CH 2 OH) where e t - is an electron trapped in the glassy matrix, e t - can migrate perceptibly but slowly through the glass at temperatures > 100 °K and can be photo-detached from the matrix by + red or u.v. light, in both cases ultimately reacting with CH 3 OH 2 . The radical • CH 2 OH becomes mobile at temperatures not less than 106 °K and reacts bimolecularly to form glycol or formaldehyde. It is decomposed by u.v. light, but reaches a stationary concentration owing to the reaction sequence • CH 2 OH + hv 1 -> H 2 + CHO; CHO + hv 2 -> CO + H*; H* + CH 3 OH-> H 2 + •CH 2 OH. Solutes may compete with the electron trapping process and also react with electrons rendered mobile by the action of heat or light on trapped electrons.