Photooxidation of formaldehyde in solid oxygen and argon/oxygen matrixes at 12 K

Abstract

Matrix-isolated formaldehyde in solid O/sub 2/, Ar/O/sub 2/, and Ar matrices at 12 K has been photolyzed by ultraviolet light in the 220-400-nm range. The photoproducts were identified by infrared spectroscopy. Stable oxidation products were CO, CO/sub 2/, H/sub 2/0, H/sub 2/O/sub 2/, O/sub 3/, and HCOOH, whereas relatively unstable products were HO/sub 2/, its hydrogen-bonded dimer (HO/sub 2/)/sub 2/, formylperoxy radical HC(O)OO, and performic acid. The observed photoproduct distribution is rationalized by the stoichiometry of chemical reactions involving one C atom, two H atoms, and odd numbers of O atoms in the cage. Photolysis of the Ar/O/sub 2//H/sub 2/CO sample (10% O/sub 2/ in solid Ar) gave poor yields of radical species. Under the experimental conditions employed, the photochemical oxidation process is not driven to completion, and therefore it is possible to trap reactive intermediates for spectroscopic and kinetic studies. Photodissociation thresholds of H/sub 2/CO and (H/sub 2/CO)/sub 2/ in solid Ar have been measured with tunable, pulsed UV laser photolysis to show that (H/sub 2/CO)/sub 2/ has a lower threshold than H/sub 2/CO.