Evidence for tunnelling motion in the rotational spectrum of the aminomethyl radical CH2NH2

Abstract

The aminomethyl radical CH₂NH₂ has been proposed to be one of the key radical intermediates in the astrophysical and atmospheric chemistry of methylamine. Its spectroscopy, however, has never been characterized by rotationally resolved experiments, impeding its potential detection in the interstellar medium by radio astronomy. We report the first rotational spectrum of CH₂NH₂ recorded and modelled between 300 and 750 GHz. The broadband acquisition of the pure rotational transitions reveals an unambiguous inversion tunnelling motion of the –CH₂ and –NH₂ groups in the radical that splits the ground vibrational state of CH₂NH₂ into two substates coupled by a Coriolis-type interaction. The careful analysis of the spectrum opens the possibility of searching for CH₂NH₂ in the interstellar medium.