Lineshape Measurements of Rotational Line in Millimeter-Wave Region by Second Harmonic Detection

Abstract

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 rotationał transition J = 6 4-5 of OCS molecule to be equal to 6.59 ± 0.25 MHz/Tr.

Pressure broadening ofJ= 1–0 rotational line of the CHF3molecule in an electric field

“…The observed width AE,,, shows a strong dependence on the modulation field strength E, and the slope-linewidth AE,, which, under the conditions of the experiment is a function of the gas pressure. Obtaining a correct value of AE,, from the measured AE,,,-values would require several diagrams AEppo(Em) to be made at various gas pressure values followed by an extrapolation to zero-modulation field [22].…”