Sub-Doppler spectroscopy of the acetaldehyde and methylamine molecules

Rotational spectra of the methylamine and acetaldehyde molecules were recorded in the frequency range between 80 and 120 GHz with sub-Doppler spectral resolution. Such resolution was achieved by means of Lamb-dip observation. The main aim of this study was to search for the torsionally mediated anomalous high-J hyperfine splittings in acetaldehyde and methylamine molecules, similar to that ones recently discovered in methanol. Our current results show that in contrast to methanol the rotational transitions of both methylamine and acetaldehyde do not have a resolved anomalous high-J hyperfine structure (besides usual quadrupole hyperfine structure in methylamine) at the current level of our resolution.