excitation of optical branch phonons

[valleyman]

As I studied, the optical branch of a crystal is called so because it can be excited with e.m. fields but I wondered whether it is possible to excite the optical branch also with chargeless particles like neutrons or the charge/action-on-charge is necessary for the process? And if so, why? I explained myself that optical modes are those in which atoms are treated differently basing on the sign of their (partial) charge so the e.m. field stimulates opposite accelerations on them and counter-phase movements can happen. I don't know if this is right, can anyone make it clearer?
Thanks
valleyman

[Rajini]

optical phonons can also be excited by charge-less particles. For example neutron inelastic scattering can be used to study optical phonons.
I dont know exactly the reason, maybe some one can explain.
PS. Maybe dipole change plays the role rather than sign.