Study of low-energy resonant metastability exchange in argon by a pulsed merging beam technique

The resonant metastability exchange process in low-energy collinear collisions between metastable argon atoms (Ar* 3P2) polarized in spin (M +2) and ground-state Ar atoms from a nozzle beam is studied by means of a time-of-flight technique. A wide range of metastable atom velocities in the laboratory frame (275 m s-1 down to 50 m s-1) is obtained by use of a Zeeman slower, the counter-propagating laser beam of which is locked in frequency onto the 3P2-3D3 closed transition (λ = 811.5 nm). The accessible centre-of-mass energy range (8-27 meV) has not been explored so far, to our knowledge. Calculations based upon existing interatomic potentials of 2g and 2u symmetries are in reasonable agreement with experiment. (fast track communication)