The radiation chemistry of liquid and glassy methanol

Abstract

The methods of pulse radiolysis, low temperature optical and electron spin resonance spectroscopy and chemical analysis of stable products have been applied to an investigation of the γ -radiolysis of liquid and glassy methanol. Processes induced by generation of presumed intermediates by photoionization of solutes have been studied using the same techniques. Electrons are trapped in glassy methanol after γ -irradiation at 77 K with a yield G(e¯ t ) = 2.7 ± 0.3 and on warming are rendered mobile, ultimately forming an amount of hydrogen equal to 1/2G(e¯ t ) . In contrast, illumination of the irradiated sample at 77 K with visible light decomposes the trapped electron, forming hydrogen and CH 2 OH or CH 2 O - in yield equal to G(e¯ t ) . The solvated electron in liquid methanol also reacts with the solvent, at a rate faster than the corresponding reaction in water. The addition of sodium methoxide to liquid methanol results in a marked increase in both the yield and lifetime of the solvated electron observed after 0.2 μ s irradiation pulse. The optical absorptions and decay parameters of CH 2 OH and CH 2 O - in liquid methanol were obtained; the ultraviolet absorption observed in irradiated methanol glass after removal of the trapped electrons by photo-bleaching is probably due to these two species. Solutions of methanol glass containing silver perchlorate exhibit complex optical and e. s. r. spectra, which provide evidence for several different species, but a complete analysis has not been possible. The radicals expected from the initial ionization event are considered. The results of this work together with published data are used to predict the reaction of the free radicals CH 3 O. , CH 2 OH, CH 2 O-, H. and e¯ s or e¯ t in the systems of interest and the relevance of these reactions to some aspects of the radiation chemistry of methanol is discussed.