Study of highly excited states of molecules by an ion-energy-loss spectroscopy

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The purpose of this study is as follows. (1) Improvement of the resolution and the brightness of an ion energy-loss spectrometer. (2) Survey of highly excited states of molecules. By modifying the ion extraction electrode of the electron impact type ion source and focussing lens system, the intensity of the ion beam was improved enough to measure energy loss spectra up to about 16eV in collisions of 2.5 keV He^+ with n_2 and CO molecules. Some unidentified peaks were found above 12 eV in N_2 molecule with the energy resolution of 60 meV.Energy spectra of H_3^+ ions in collisions with rare gases (He, Ne, Ar, Kr and Xe) were measured. In the energy range of 0-1 eV of energy loss and gain sides, broad peaks were observed. These peaks may be due to the excitation and de-excitation among ro-vibronic states of H_3^+. This fact suggests that about half of H_3^+ ions formed in the ion source are excited states. In addition to these peaks, broad energy loss peaks located at around 10 eV were observed for Ar, Kr and Xe targets. These peaks are attributed to simultaneous transitions of the excitation in the targets and the excitation or de-excitation in the projectile H_3^+ ions.