Wavelength-Dependent Photolysis of Methylglyoxal in the 290−440 nm Region

Abstract

Photodissociation of methylglyoxal (CH3COCHO; MGLY) in the 290−440 nm region has been investigated at 10 nm intervals by using dye laser photolysis in combination with cavity ring-down spectroscopy. Absorption cross sections of methylglyoxal were obtained at each wavelength studied. The HCO radical was a photodecomposition product. The formation yield of HCO, determined by monitoring its absorption at 613.8 nm, decreased with increasing MGLY pressure in the 1−10 Torr range. The HCO yields (extrapolated to zero MGLY pressure) were unity in the 320−360 nm region, consistent with the photodissociation mechanism CH3COCHO + hν → CH3CO + HCO (P1). The HCO yields decreased at both the shorter (290−310 nm) and the longer (370−440 nm) wavelength end. The dependence of the HCO yields on nitrogen buffer gas pressure was also examined. The HCO radical yields were independent of nitrogen pressure (10−400 Torr) between 290 and 370 nm, but decreased with increasing nitrogen pressure in the 380−440 nm region. The coeffic...