Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See page_maxonapi_getting_started_foundations_cinema_parameters.
Parameter: Particle Object
FIELDLAYER_PARTICLE_OBJECT
Parameter: Mode
FIELDLAYER_PARTICLE_SOURCE_MODE
Parameter: Map UniqueID
FIELDLAYER_PARTICLE_SOURCE_MODE_INDEX_MAP_UNIQUE
Parameter: Use Particle Radius
FIELDLAYER_PARTICLE_USE_PARTICLE_DISTANCE
Parameter: Radius
FIELDLAYER_PARTICLE_DISTANCE
Parameter: Value Source
FIELDLAYER_PARTICLE_SOURCECHANNEL_VALUE
Parameter: Color Source
FIELDLAYER_PARTICLE_SOURCECHANNEL_COLOR
Parameter: Direction Source
FIELDLAYER_PARTICLE_SOURCECHANNEL_DIRECTION
Parameter: Clip to Shape
FIELDLAYER_PARTICLE_CLIP
Parameter: Color Alpha
FIELDLAYER_PARTICLE_COLOR_ALPHA