High-resolution translational energy spectroscopy (0.1 eV full width at half maximum) has been performed on 3 keV C+ ions scattered off NZ molecules. The intriguing energy loss spectrum with well-resolved vibrational structure is explained on the basis of simultaneous transitions involving changes of states in the C+ ion and the Nz molecule.It is well known', that collisional excitation of N2 by proton impact results in the dominant Lyman-Birge-Hopfield transition X'C; -+ a'n, between the ground and lowest singlet excited state of the molecule. The triplet states B3n, and A3Z:, which lie below the singlet state a'&, are not accessible by proton impact on account of spin-conservation requirement^.^ In collisions with positive ions in nonsinglet ground states (e.g., He+, AT+), singlethiplet transitions of N2 can occur without violation of spin-con~ervation,~ and indeed the Vegard-Kaplan (X'2:,'4A3CC:) and first positive (X'Ci-+B311,) transitions are prominent in the energy-loss spectra.In this brief communication, we present an unusual energy-loss spectrum (see Fig. 1 (a and b)) obtained for 3 keV C+ ions in collision with N, molecules, using high-resolution translational energy spectroscopy with an energy resolution of 0.1 eV full width at half maximum (FWHM). The vibrational structures are adequately resolved and the average spacings between vibrational levels sufficiently accurately determined to allow confident identification of the relevant transitions. EXPERIMENTALThe experiments were performed in a novel doublefocussing mass and translational energy spectromete3 based on a symmetrical arrangement of two identical analysers. The instrument has been described in a recent publication.6 Briefly, C+ ions were generated from CH, in a low-pressure electron-ionization source from which they were extracted and accelerated through 3 kV. Following mass analysis by a magnetic sector, the ions were passed through an electrostatic monochromator and a collision gas-cell containing low pressure Torr) target N2 gas to ensure singlecollision conditions. Energy analysis of the scattered C+ ions was performed by scanning in tandem two electrostatic analysers, the second of which was used to eliminate low-level interferences which may be caused by reflection of ions and/or neutral species from walls and slits.*Author to whom correspondence should be addressed at: Physics Department, La Trobe University, Victoria 3083, Australia. RESULTS AND DISCUSSIONThe translational energy spectra (TES) for 3 keV C+ ions on N2 are shown in Fig. 1 (a and b). The spectrum for the full energy range is displayed in (

The resonance spectrum of a finitely periodic superlattice system is analysed for the special case where each period is made up of N identical "structure" potential cells terminated by one different "impurity" cell. It is shown that the effect of the impurity is to re-group the resonances of the corresponding "undoped" structure, in which all "impurity" cells are replaced by "structure" cells. The close relation to band splitting in the infinitely periodic limit is discussed.Das Resonanzspektrum eines endlichen periodischen Superlattice-Systems wird analysiert fur den besonderen Fall, daR jede einzelne Periode aus N identischen ,,Struktur"-Potentialzellen endend mit einer anderen ,,Fremdatomzelle" besteht. Es wird gezeigt, daR die Wirkung des Fremdatoms darin besteht, die Resonanzen der entsprechenden undotierten Struktur neu zu gruppieren, so daR alle ,,Fremdatomzellen" durch ,,Struktur"-Zellen ersetzt werden. Die nahe Beziehung zur Bandaufspaltung fur den unendlichen periodischen Grenzfall wird diskutiert.

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