Nonresonant ionization detected IR spectroscopy for the vibrational study in a supersonic jet

A spectroscopic technique for the measurement of the IR transition in a supersonic jet has been developed. This spectroscopy, the nonresonant ionization detected IR spectroscopy (NID-IR), detects the IR transition by selective ionization of the vibrationally excited molecule. Because of the ionization detection, it has high sensitivity. Furthermore, the ionization detection allows one to observe the IR spectrum of a specific molecular species by selecting the mass of the corresponding cation. The advantage of NID-IR spectroscopy has been demonstrated by the observation of IR spectra of phenol, o-fluorophenol, acetylene and 7-azaindole in a supersonic jet. The assignments of cis and trans rotational isomers in o-fluorophenol are also discussed.