Quantify argon-metastable-mediated methane dissociation

Determine the argon-metastable density and quantify the contribution of Penning dissociation by argon metastables to the sustained atomic-hydrogen production in the negative-glow region of the Ar–CH4 short glow discharge.

Background

The negative glow contains energetic electrons but a weak electric field, so direct electron-impact dissociation is supplemented potentially by non-local transport of long-lived argon metastables from the sheath. The proposed reaction is Ar* + CH4 → Ar + CH3 + H, along with related channels.

The contribution of this mechanism has not been quantified because the argon-metastable density is not measured. The paper identifies laser-induced fluorescence of the Ar 4s states as the future diagnostic needed to resolve this contribution.