Measurement of Radical Quantum Yields from Formaldehyde Photolysis between 269 and 339 nm

Abstract

The relative quantum yield for the production of radical products, H and HCO, from the photolysis of formaldehyde (HCHO) has been measured directly at wavelengths from 269 to 339 nm. Measurements of the radical products were conducted using chemical amplification with subsequent detection by chemical ionization mass spectrometry (CIMS). All yields were measured at a pressure of 50 Torr and were normalized to a quantum yield of 0.753 at 303.75 nm based on the recommendation of DeMore et al.1 The quantum yields were measured with sufficient wavelength resolution (± 0.62 nm, fwhm) to observe structure which had been previously unreported and is believed to provide evidence for a complicated competition among the various dissociation pathways to H + HCO, H + H + CO and H2 + CO, as well as with quenching to the ground state. The quantum yields measured should aid in the calculation of formaldehyde photolysis rates in the troposphere and are estimated to result in increases of at least 8% in calculated H/HCO production.