Evidence of a weak electronic density distortion in polymerized A 1C 60 (A=K and Rb) compared to pristine C 60

Abstract

Compton profile measurements on K 1C 60 and Rb 1C 60 and C 60 powders have been carried out using inelastically scattered photons. We compare experimental Compton Profile Difference (CPD) of K 1C 60 and that of C 60 with the corresponding calculated results, obtained from ab initio self-consistent field calculations of the energy band structure. This permits us to isolate the contribution of the distortion of the C 60 orbitals for each compound and to compare them. In previous paper, we have shown that for A n C 60 compounds this approach leads to a good agreement between theory and experiment. In this paper, we show that it is not the case for K 1C 60. The distortion contribution is overestimated by calculations leading to a CPD narrower than the experimental one. Furthermore similar measurements performed on heavy ions intercalated compounds (Rb 1C 60) show clearly that CPD depends on the number of ions and not on their nature. We think that our results corroborate the conclusions of a very small distortion of C 60 molecules in the polymerized phase obtained by neutron diffraction experiments by Fox et al. (Chem. Phys. Lett. 249 (1996) 195).