Lineshape Measurements of Rotational Line in Millimeter-Wave Region by Second Harmonic Detection
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Lineshape measurements of the J = 6 ← 5 OCS rotational transition were performed using a source-modulation microwave spectrometer. This is a very useful experimental technique but it introduces distortions to the line profile, therefore several authors have theoretically analyzed this problem with the aim of extracting the undistorted parameters of the spectra. The objective of this paper is to verify one of these theories which gives the relationship between harmonic signals and lineshape over wide range of modulation depth. Detailed comparison between the calculated and experimental harmonic signals shows very good agreement, and thus enables us to determine the unmodified line width and finally the pressure broadening factor of the rotational transition J = 6 ← 5 of OCS molecule to be equal to 6.59 ± 0.25 MHz/Tr.
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