ISSN:
1432-0630
Keywords:
PACS: 61.46.+w; 76.60.-k
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
\chem{\chemvar{A}C_{60}} with \chem{\chemvar{A}}=\chem{K} , \chem{Rb} , \chem{Cs} . From the temperature dependent \isotope{13}{C} line shift of \chem{RbC_{60}} we have extracted information about the electron density distribution on the \chem{C_{60}} molecules. The data also support the existence of an \orbital{sp}{3}{} like bonding type between the molecules. The magnetic phase transition observed at low temperature in \chem{RbC_{60}} and \chem{CsC_{60}} is monitored by an increase of the second moment as well as an increase of the spin lattice relaxation rates of the \isotope{13}{C} and alkali nuclei. The results are compared to \isotope{13}{C} NMR data of \chem{KC_{60}} where no signs of a magnetic ordering are found. The magnetically ordered phases are discussed in terms of antiferromagnetic spin density wave. We also report on \isotope{13}{C} NMR measurements of orthorhombic one dimensional and rhombohedral two dimensional polymers of \chem{C_{60}} obtained under high pressure. By spinning the samples up to \valunit{12}{kHz} , we are able to identify two resonances at \valunit{146}{ppm} and \valunit{73.5}{ppm} for the orthorhombic polymer and six resonances at \valunit*{149.1}{ppm} , \valunit*{147.9}{ppm} , \valunit*{145.2}{ppm} , \valunit*{139.6}{ppm} , \valunit*{134.8}{ppm} and \valunit{73.5}{ppm} for the rhombohedral one. The static distortion of the \chem{C_{60}} molecules induced by the transformation under pressure must be at the origin of the observed inequivalent carbons in both systems. The \isotope{13}{C} NMR lineshape simulations of the obtained spectra are compatible with the suggested polymeric structures where the \chem{C_{60}} molecules are connected by [2+2] cycloadditions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s003390050481
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