Evidence of a weak electronic density distortion in polymerized A1C60 (A=K and Rb) compared to pristine C60

Abstract Compton profile measurements on K 1 C 60 and Rb 1 C 60 and C 60 powders have been carried out using inelastically scattered photons. We compare experimental Compton Profile Difference (CPD) of K 1 C 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 1 C 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 1 C 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).