Laser spectroscopy of molecular ions

This review describes how laser induced fluorescence spectroscopy at three different temperatures, near room, near liquid N2, and near liquid He, can provide remarkable new information about the quantum states of molecular ions. The experimental techniques are described whereby gas phase spectra can be obtained at the two higher temperatures, and matrix isolation spectra at the lowest temperature. A critical analysis is presented of the conditions necessary for the matrix spectra to be considered low temperature limits of the gas phase spectra. An overview is given of the various sorts of information obtained by laser spectroscopy, which include quantum state selective detection of molecular ions, electronic and vibrational frequencies, Jahn-Teller effects, and vibrational relaxation