Argon luminescence bands between 1600 and 2900 Å

It is proposed that the luminescence bands observed in high-pressure argon between 1600 and 2900 Å are due to transitions involving excited states, Ar 2 + *, of the molecular ion, Ar 2 + : the initial state is a bound state having a 2 S- 2 S 0 ion-atom asymptote and the final states two of the first set of molecular ion states which dissociate to the ion-atom pair 2 P- 1 S 0 . This assumption accounts for most known experimental data on this emission band. The competition between the radiative transitions and the quenching collisions between the excited ions and electrons in alpha -particle tracks has been studied experimentally and is discussed in terms of the present hypothesis. A comparison is also made between the neutralisation of excited and ground-state molecular ions.