Absorption Cross Sections of Formaldehyde at Wavelengths from 300 to 340 nm at 294 and 245 K

Absorption cross sections for the Ã1A2−X̃1A1 electronic transition of formaldehyde have been measured by
ultraviolet (UV) laser absorption spectroscopy in the tropospherically significant wavelength range 300−340
nm, over which HCHO is photochemically active. Absorption cross sections are reported at two temperatures,
294 and 245 K and at a spectral resolution of 0.0035 nm (0.35 cm-1). At this resolution, greater peak absorption
cross sections are obtained for many of the sharp spectral features than were previously reported. To simulate
atmospheric conditions in the troposphere, the effects of adding a pressure of nitrogen of up to 500 Torr and
of reduced sample temperature were investigated. The overall magnitudes of peak absorption cross sections
are largely unaffected by the added pressure of nitrogen, but a modest degree of pressure broadening (0.2−0.3 cm-1 atm-1) is evident in the line shapes. Computer simulations of spectra have been optimized by
comparison with wavelength-dependent formaldehyde absorption cross sections for each major vibronic band
in the chosen wavelength range. Experimental and computer simulated spectra at 294 and 245 K are compared
to test the reliability of the computer simulations for quantification of the effects of temperature on absorption
cross sections. All experimental absorption cross section data and tables of input parameters for spectral
simulations are available as Supporting Information.