Electric Resonance Spectroscopy of Hypersonic Molecular Beams

A hypersonic nozzle beam (Mach 19) of HCN molecules was studied by electric resonance spectroscopy. Translational temperatures of 4°K and rotational temperatures of $\text{64± 30°}\mathrm{K}$ were found from a 283°K nozzle source. The monoenergetic character of the beam and the rotational cooling lead to an order of magnitude increase in signal‐to‐noise ratios. The absence of an appreciable velocity dispersion and a homogeneous radiation field allowed a critical comparison with theoretical two‐level resonance lineshapes. An SF₆ diluent was used to reduce the beam velocity by one‐half and increase spectral resolution over a thermal (effusive) source. SF₆ vibrational relaxation was observed. Chemically interesting species can be formed: ArXe, XeHCl, (HCl)₂, (HCN)_x, and (HF)_x.