Inelastic processes occuring in thermal-velocity metastable atoms and molecules passing at a mean distance (1–100 nm) are investigated. These processes are caused by the quadrupolar part of the van der Waals interaction: fine-structure transitions in atoms (Ar∗, Kr∗), rovibrational transitions in N 2 ∗ ( 3 Σ u + ), transitions among magnetic sub-levels in the presence of a magnetic field.
