Improved mid-infrared cross-sections for peroxyacetyl nitrate (PAN) vapour

[摘要] Absorption spectra of peroxyacetyl nitrate (PAN, CH₃C(O)OONO₂)vapour at room temperature (295K) have been measured in the mid-infraredrange, 550-2200cm^-1 (18.2-4.55µm), using a Fourier Transforminfrared spectrometer at instrument resolutions of 0.25 and 0.03cm^-1(unapodised). Between five and eight measurements were obtained for eachspectral band of PAN in the pressure range 0.24-2.20mb showing goodagreement with Beer's law. Both cross-section data and integrated absorptionintensities for the five principal bands in the PAN spectra in this spectralrange have been derived with peak cross-sections of the 794, 1163, 1302,1741 and 1842cm^-1 bands measured to be 0.95(±0.02), 1.21(±0.03),0.92(±0.02), 2.39(±0.06) and 0.74(±0.03) (x10^-18cm²molecule^-1)respectively. Band intensities andband centre absorptivities are also reported for four weaker PAN absorptionbands in the mid infrared for the first time. These observations are thehighest spectral resolution measurements of PAN bands reported in theinfrared to date. For three of the five strongest bands, the absoluteintegrated absorption intensities are in excellent agreement with previousstudies. A 4.8% lower integrated intensity was found for the 1741cm^-1ν_as(NO₂)PAN absorption band, possibly as a result of theremoval in this work of spectra affected by acetone contamination, while a10.6% higher intensity was determined for the 1163cm^-1ν(C-O)absorption band. No resolution of fine structure in the PAN absorption bandswas observed at the resolutions studied. The confirmation of absorptioncross-sections and estimated errors in this work will allow more accurateinvestigations of PAN using infrared spectroscopy, particularly for remotesensing of PAN in the atmosphere.

[学科分类] 大气科学