We have measured the reaction rate coefficient for Penning ionization of argon atoms in collisions with metastable helium atoms. This experiment is motivated by the planned studies of the state-selective dissociative recombination (DR) rate of ortho- and para-H3+ ions with electrons under 50 K.
A stationary afterglow (SA) apparatus was utilized in present studies. The measurement of the number densities of ions and of electrons is carried out by continuous wave cavity ring-down spectroscopy and microwave diagnostics, respectively.
The measured Penning ionization reaction rate coefficient was of the order of 10-10 cm3s-1, which is in agreement with the typical rates for Penning ionization.