Phonon line shape in disordered

We present a calculation of the H_gphonon self-energy for a model of A₃C₆₀(A=K, Rb). The orientational disorder of the C₆₀molecules is included, and the lowest order self-energy diagram is considered. The calculations illustrate that due to the violation of momentum conservation by the orientational disorder, Raman scattering can measure the decay of a phonon in an electron-hole pair, allowing the estimate of the electron-phonon coupling from such experiments. Comparison with experimental line shapes further provides support for a local correlation of the molecular orientations, with neighboring molecules preferentially having orientations differing by a 90°rotation.