Lineshape measurements of rotational lines in the millimeter-wave region by second harmonic detection

Abstract Lineshape measurements of OCS rotational transitions have been carried out by using frequency modulation and comparing the experimental second harmonic signal to the computed second Fourier component of a modulated Voigt profile. The asymmetry of the spectral lines has been accounted for by adding to the lineshape model a suitable distortion term. The modulation amplitude values which provide good agreement between the experimental and the computed spectra have been found. The self-broadening coefficients of the J = 8 ← 7, 12 ← 11, and 16 ← 15 ground state transitions of OC 34 S and O 13 CS have been determined.