Article pubs.acs.org/JPCA
IR Absorptions of C+60 and C−60 in Neon Matrixes Bastian Kern, Dmitry Strelnikov,* Patrick Weis, Artur Böttcher, and Manfred M. Kappes Institute of Physical Chemistry II, Karlsruhe Institute of Technology, Fritz-Haber-Weg 2, 76131 Karlsruhe, Germany S Supporting Information *
ABSTRACT: C+60 ions were produced by electron-impact ionization of sublimed C60, collimated into an ion beam, turned 90° by an electrostatic deflector to separate them from neutrals, mass filtered by a radio frequency quadrupole, and co-deposited with Ne on a cold 5 K gold-coated sapphire substrate. Infrared absorption spectroscopy revealed the additional presence of C60 and C−60 in the as-prepared cryogenic matrixes. To change the C+60/C−60 ratio, CCl4 or CO2 electron scavengers were added to the matrix gas. Also taking into account DFT calculations, we have identified nine new previously unpublished IR absorptions of C+60 and seven of C−60 in Ne matrixes. Our measurements are in very good agreement with DFT calculations, predicting D5d C+60 and D3d C−60 ground states. The new results may be of interest regarding the presence of C60 and C70 (as well as ions thereof) in Space.
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INTRODUCTION A new experimental setup for studies of mass-selected matrixisolated species (DEPO-2) has recently been built in our laboratory. As a test system, we decided to first study C+60 and C−60 because these ions have already been investigated in the NIR1−3 and mid-IR3,4 regions, and we have also had some experience in creation and mass-selected deposition onto UHVclean surfaces of IPR (isolated pentagon rule) and non-IPR fullerenes.5 IR spectroscopy of neutral and charged C60, mostly in the solid state, has been reviewed by Kuzmany et al.6 Electrochemical reduction of C60, followed by UV−vis−NIR, ESR, and Raman spectroscopy of the resulting charged species has also been well-studied and is reviewed by Kaven and Dunsch.7 Gas-phase laser NIR spectroscopy has been 9 performed in an electrostatic storage ring for C−608 and C2− 60 . − Gas-phase IRMPD (infrared multiphoton dissociation) of C60 has been done using a free electron laser.4 On the other hand, there is as yet no gas-phase laboratory absorption data for C+60 in IR and UV−vis−NIR spectral regions. Recently, C60 has also been found in several stellar nebulae by mid-IR satellite-based surveys,10−12 thus making studies of the corresponding cations of renewed interest for astronomers and astrophysicists. Our data, partly presented at a recent conference,13 was already used to detect C+60 in the Tc1 young planetary nebula, Small Magellanic Cloud14 and in the NGC 7023 reflection nebula.15 Here, we present a comprehensive description of our measurements and of further new laboratory data on C+60 and C−60.
Figure 1. Experimental setup DEPO-2.
were sublimed out of a Knudsen cell and ionized by 50 eV electrons. The cations were guided by electrostatic lenses through three stages of differential pumping, an electrostatic bender (to exclude neutrals), and a quadrupole mass filter (Extrel, in order to exclude positively charged fullerene fragments, mostly C+58 and doubly charged species C2+ 60 ). They were then co-deposited with matrix gas (Pmatrix gas ≃ 5 × 10−5 mbar) onto a cold substrate at a nominal incident kinetic energy of
