Titelaufnahme

Using a wire-based cryogenic radiofrequency ion trap we have studied helium tagging of protonated glycine ions, GlyH+, at low temperatures. Time-of-flight mass spectrometry of the trapped ions shows tagging with up to four helium atoms at trap temperatures down to 3 K. From temperature-dependent ion intensities an activation energy for collision-induced dissociation is derived. A pulsed infrared laser has been used to study the OH stretching vibration by vibrational predissociation spectroscopy in trapped GlyH+(He)n ( to 3), and only small shifts of the center frequency have been observed. The width of the absorption peak is explained by the simulated rotational contour of the absorption band of the trapped ions with about 6 K rotational temperature. Quantum chemical calculations of the structures of the GlyH+(He)n ( to 3), the different helium binding energies, and the frequency shifts of the OH stretching vibration have been performed and found to explain the observed features qualitatively.