Radiolysis of aqueous formaldehyde relevant to cometary environments

Abstract

The radiation chemistry of aqueous solutions of formaldehyde was studied in order to obtain an insight into the possible role of ionizing radiation on cometary environments. Aqueous solutions of 1.0 mol dm −3 formaldehyde were exposed to γ-radiation in the dose rage from 0.01 to 1200 kGy at 298 K. The radiation chemical yield of decomposition of formaldehyde was determined to be: G(−CH 2(OH) 2) = 26.3±1.2. The high radiation chemical yield of decomposition was explained by a chain reaction initiated by the radical ·CH(OH) 2 with formaldehyde. Computer fitting of the experimental data gives k(·CH(OH) 2 + CH 2(OH) 2) = 8.0×10 1 dm 3 mol −1 s −1. In the computer treatment of experimental findings we used 54 equations to consider the radiolysis of water and 11 reactions for the radiolysis of aqueous formaldehyde. Based on previous estimates of the total dose of ionizing radiation that comets have accumulated over 4.6 billion years, we predict a radiation damage-depth curve of formaldehyde in comet nuclei.