Some approaches to spectroscopic characterization of polyatomic cations

Abstract

Spectroscopic approaches aimed at vibrational and rotational characterization of open-shell polyatomic cations by means of their electronic transitions are described. Two of the techniques used rely on the detection of the fluorescence of the electronically excited cations in the gas phase. These are based on emission spectroscopy using electron impact excitation to probe rotationally cooled ions in supersonic free jets and to investigate ions of unstable molecules, and on laser excitation spectroscopy on ions produced by Penning ionisation and collisional relaxation. With the latter method rotational studies of the electronic transitions of some tri- and tetra-atomic ions have also been carried out. In the case of the non-fluorescing ions, the electronic transitions can be followed in absorption in neon matrices at 5 K. Examples of such studies and the information forthcoming are given.