Absolute measurements of absorption at the iodine-laser frequency in atmospheric gases

The absorption cross sections at the chemical-iodine-laser frequency for methane and carbon dioxide in an atmosphere of dry air were determined with a photoacoustic cell to be (8 + or - 2) x 10 to the -24 and (5.4 + or - 0.4) x 10 to the -25th sq cm, respectively. A multipass absorption cell and a Fourier-transform spectrometer were used to obtain a cyclopropane absorption cross section (3.47 + or - 0.02) x 10 to the -24th sq cm at 14 076/cm for the photoacoustic-cell calibration.