There is already a preset in CINEMA 4D to achieve this. It consists of two parts.
First the deflection of the particle which is done with PDeflector. To keep the particle from bouncing it is set to a high surface value.
The second part is the alignment of the particle so it can move parallel to the surface. This is done in the XGroup called Alignment Adjustment. In there the new alignment of the particle is calculated from it's velocity normal and the collision normal.
The complete scene includes a planar gravity along y-axis as well as particle collision to achieve more natural behaviour of the particles.
Scenefile (C4D 133 KB) Movie (QT 714 KB)