  The Coma cluster is the richest and most compact of the nearby clusters, yet
there is growing evidence that its formation is still on-going. A sensitive
probe of this evolution is the dynamics of intracluster stars, which are
unbound from galaxies while the cluster forms, according to cosmological
simulations. With a new multi-slit imaging spectroscopy technique pioneered at
the 8.2 m Subaru telescope and FOCAS, we can now detect and measure the
line-of-sight velocities of the intracluster planetary nebulae which are
associated with the diffuse stellar population of stars, at 100 Mpc distance.
We detect significant velocity substructures within a 6 arcmin diameter field,
centred on the Coma X-ray cluster emission. One substructure ispresent at ~5000
km/s, probably from infall of a galaxy group, while the main intracluster
stellar component moves at ~ 6500 km/s. Hence the ICPNs associated with the
diffuse light at the position of the MSIS field are not bound to the nearby cD
galaxy NGC 4874, whose radial velocity is ~ 700 km/s greater.
