Low energy collisions of spin-polarized metastable argon atoms with ground state argon atoms

The collision between a spin-polarized metastable argon atom in Ar∗ (3p⁵4s, ³P₂, M = +2) state slightly decelerated by the Zeeman slower-laser technique and a co-propagating thermal ground state argon atom Ar (3p⁶, ¹S₀), both merged from the same supersonic beam, but coming through adjacent slots of a rotating disk, is investigated at the center of mass energies ranging from 1 to 10 meV. The duration of the laser pulse synchronised with the disk allows the tuning of the relative velocity and thus the collision energy. At these sub-thermal energies, the 'resonant metastability transfer' signal is too small to be evidenced. The explored energy range requires using indiscernibility amplitudes for identical isotopes to have a correct interpretation of the experimental results. Nevertheless, excitation transfers are expected to increase significantly at much lower energies as suggested by previous theoretical predictions of potentials 2g(³P₂) and 2u(³P₂). Limits at ultra-low collisional energies of the order of 1 mK (0.086 μeV) or less, where gigantic elastic cross sections are expected, will also be discussed. The experimental method is versatile and could be applied using different isotopes of Argon like ³⁶Ar combined with ⁴⁰Ar, as well as other rare gases among which Krypton should be of great interest thanks to the available numerous isotopes present in a natural gas mixture.