TEMPERATURE-DEPENDENT FORMALDEHYDE CROSS-SECTIONS IN THE NEAR-ULTRAVIOLET SPECTRAL REGION

The near-ultraviolet (300-360 nm, 33 300-27 800 cm-1) absolute absorption cross sections for formaldehyde (CH2O) have been measured as a function of temperature (223-293 K), and formaldehyde concentration in nitrogen at 500 Torr. Fourier transform spectroscopy was performed using an instrumental resolution sufficiently high (1.00 cm-1 or approximately 0.011 nm at 330 nm) to ensure the cross sections which are used in calculated atmospheric photolysis rates are free of artifacts due to overlap (or lack thereof) in the spectral structure of the solar flux or in the structure of the formaldehyde absorption spectrum. Comparisons with previous measurements are made and recommendations presented for use in atmospheric photolysis rate calculations. Representative ground-level photolysis rates are calculated and compared in order to ascertain the effect of the temperature dependence in the absorption cross sections as well as the effect of integration interval. © 1990 American Chemical Society.