Pressure broadening of the NO2 hyperfine multiplet at 93 GHz

Line shapes of the hyperfine NO₂ 26(1,25)←25(2,24) rotational transition have been measured at pressures below 3 torr with a bridge spectrometer originally designed for direct absolute absorption studies. The multiplet consists of six lines with δF=δJ=δN=1 in the vicinity of 93,445 MHz. The same line-broadening parameter of 3.7 MHz/torr and the same maximum absorption of 1.8×10^-5 cm^-1 have been found for all 6 lines. The maximum absorption of the strongly overlapped multiplet at a pressure of 10 torr was measured to be 1.06×10^-4 cm^-1, in good agreement with the theoretical value. The interference effect of the overlapping lines turns out to be below ?10%, so that a simple superposition of lorentzian shapes is a good approximation for this case. The remaining difference can be compensated for by the introduction of an overlap parameter for each line.