engleski

Theory of highly charged ion gain spectroscopy of molecular collective excitations

This paper discusses the physical mechanism by which a highly charged, energetic ion partly neutralized by electron transfers from a large molecule can create molecular collective excitations in the process. Our analysis offers a new explanation for the periodic oscillations observed by Selberg et al Phys. Rev. A53, 874 (1996) in the high-resolution energy gain spectra of energetic Arq+ ions (q = 8, 13, 14, 15) flying-by C60 molecules and undergoing partial neutralization. For the Arq+ → Ar(q-s)+ spectra with q = 13 to 15 and s = 1 or 2, the 6 eV oscillations are assigned to energy losses due to multiple, Poissonian excitations of C60 -plasmons (6 eV quantum). These losses are subtracted from the energy gain due to the transfer of one or two-electrons to increasingly deep Rydberg states of the ion. The observed 3 eV periodicity for q = 8 arises from the peculiar Rydberg energy level spectrum of ArVIII. The first few shallow levels of this ion are separated by 3eV, while some of the pairs of adjacent, deeper levels are also separated by about 3 eV. Each pair produces two interdigitated, Poissonian series of 6 eV -plasmon loss peaks showing an apparent periodicity of 3 eV. The -plasmons (25 eV quantum) are found to contribute mainly to the medium and high energy regions of the observed spectra. The physical model analysed here indicates that collective excitations could be studied in several other systems by highly charged ion energy gain spectroscopy at sufficient resolution.

ion spectroscopy ; energy gain ; plasmon excitations

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