Development of Autoionization-Detected Infrared Spectroscopy for Molecular Cations

点击翻译按钮获取中文摘要

A new technique for infrared spectroscopy of isolated bare molecular ions in a supersonic jet was developed. High Rydberg states, of which ion core has the same structure as the corresponding bare ion, were state-selectively pumped by two-color double resonance excitation. Infrared absorption of the ion core was measured by detecting molecular ions produced by vibrational autoionization. By using this technique, which is called "autoionization-detected infrared (ADIR) spectroscopy", the following results have been obtained ;(a) The OH stretching vibrations of fluorophenol and methoxyphenol cations were observed, providing the first direct evidence for intramolecular hydrogen bonds in molecular cations.(b) The OH stretching vibration of the cresol cation was observed, and it was found that the OH frequency showed clear dependence on the orientation to the neighboring methyl group. This result indicates the presence of a new type of intramolecular hydrogen bonding between the hydroxyl and methyl groups.(c) The first observation of CH stretching vibrations in aromatic cations were performed. The aromatic and alkyl CH stretches in the ethyiphenol cation were observed, and the aromatic CH showed high-frequency shifts upon the ionization.