Abstrakt
First results from a new ion trap instrument are presented. With this instrument, ions cab be cooled to temperatures below 4K using helium buffer gas.
Low temperatures and high densities lead to efficient formation of helium-tagged ions allowing us to record infrared predissociation spectra of highly reactive species. After a short description of the instrument and its special features, the first IRPD spectrum of a small hydrocarbon dication, C7H62+, is presented.
The spectral features observed between 2900 and 3200 cm(-1) indicate that this dication corresponds to doubly ionized cycloheptatrienylidene. Several DFT methods and the MP2 method are applied to study the effect of helium tagging.
The results suggest that the effect of helium on the structure as well as on the IR spectrum of the dication is only minor; most probably in the range of the errors of the theoretical models.