Infrared absorption spectroscopy of molecular ions using tunable lasers

Abstract

For many years molecular ions have represented a challenge to the high-resolution spectroscopist. Their high reactivity makes it difficult to generate sufficient concentrations in the laboratory for traditional gas-phase spectroscopy in all but a few cases. During the past five years, however, advances in infrared laser technology and the development of sensitive experimental methods to identify absorptions by charged species have led to the observation of the infrared spectra of approximately forty molecular ions. Many of them had not been detected previously except in mass spectrometric studies. In this paper the experimental methods and results are reviewed and the type of information obtainable is illustrated by reference to recent results for the H₃O⁺(D₃O⁺) and CO⁺ ₂ molecular ions.