Rotationally Resolved Absorption Cross Sections of Formaldehyde in the...

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Co, D. T., T. F. Hanisco, J. Anderson, and F. Keutsch (2005), Rotationally Resolved Absorption Cross Sections of Formaldehyde in the 28100-28500 cm-1 (351-356 nm) Spectral Region: Implications for in Situ LIF Measurements, J. Phys. Chem. A, 109, 10675-10682, doi:10.1021/jp053466i.

The rotationally resolved ultraviolet absorption cross sections for the 200410 vibrational band of the A1A2X1A1 electronic transition of formaldehyde (HCHO) at an apodized resolution of 0.027 cm-1 (approximately 0.0003 nm at 352 nm) over the spectral range 28100-28500 cm-1 (351-356 nm) at 298 and 220 K, using Fourier transform spectroscopy, are first reported here. Accurate rotationally resolved cross sections are important for the development of in situ HCHO laser-induced fluorescence (LIF) instruments and for atmospheric monitoring. Pressure dependence of the cross sections between 75 and 400 Torr at 298 K was explored, and an average pressure broadening coefficient in dry air of 1.8 × 10-4 cm-1 Torr-1 for several isolated lines is reported. Gaseous HCHO was quantitatively introduced into a flow cell by evaporating micronsized droplets of HCHO solution, using a novel microinjector technique. The condensed-phase concentrations of HCHO were determined by iodometric titrations to an accuracy of <1%. Accuracy of the measured absorption cross sections is estimated to be better than (5%. Integrated and differential cross sections over the entire band at low resolution (∼1 cm-1) obtained with our calibration technique are in excellent agreement with previous measurements. A maximum differential cross section of 5.7 × 10-19 cm2 molecule-1 was observed at high resolutionsalmost an order of magnitude greater than any previously reported data at low resolution.

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Upper Atmosphere Research Program (UARP)