Mechanism for the decay of Ar(3P2) atoms in pure argon. Reconciliation of low pressure and high pressure values for the decay constant

A new set of decay constant values for Ar(3P2) in pure argon at 298 K determined by means of single frequency cw laser probe spectrophotometry in the 100–700 Torr region is reported. An excimer forming mechanism initiated by a reversible termolecular step and carried forward by a sequence of reversible collisional relaxation stages with provision for radiative decay at each stage is proposed to account for the kinetic behavior of Paschen-1s atoms. It is demonstrated that this mechanism is quantitatively consistent with measured collisional decay constant values at pressures in the 0–22 and 100–700 Torr regions and that adherence of such values to form, k3P2=AP2+BP, is fortuitous and that the values of A and B have no mechanistic significance. It is similarly indicated that the nature of the probable decay mechanism precludes the possibility of recovering excited atom precursor decay constant values by analysis of excimer emission and absorption data without detailed numerical modeling.