Energy pooling in an equilibrium-coupled system between Ca[4s3d(1D2)] and Mg[3s3p(3Pj)] atoms following pulsed dye-laser excitation

Abstract

We present a kinetic study of energy pooling in the equilibrium-coupled system: Ca[4s3d(¹D₂)]+ Mg[3s²(¹S₀)]⇌ Ca[4s²(¹S₀)]+ Mg[3s3p(³P_J)] following pulsed dye-laser excitation of both Mg(³P_J) and Ca(¹D₂) atoms at λ= 457.1 nm. [Mg(³P₁)â†� Mg(¹S₀)] and λ= 457.5 nm [Ca(¹D₂)â†� Ca(¹S₀)] in the presence of helium across the temperature range 800–1100 K. Quantitative characterisation of decay profiles for Mg(³P_J) and Ca(¹D₂) by time-resolved emission measurements at the above wavelengths using boxcar integration indicates the effectively instantaneous establishment and maintenance of the near-resonant equilibrium under all conditions of temperature and pressure via the observed equality in the first-order decay coefficients for removal of both states. Energy pooling into some 16 higher-lying states of magnesium and calcium, including atomic levels close to the energetically accessible limit, were observed and their temporal behaviour characterised. With the exceptions of Mg[3s4s(³S₁)] and Ca[4s4p(¹P₁)] atoms, all these pooled states exhibited first-order kinetic behaviour. Measured first-order decay coefficients for these pooled states were found to be always twice those of the energy store states, indicating their production via collisions involving the metastable states Mg(³P_J), Ca(¹D₂) and possibly Ca(³P_J). Initial relative populations of energy-pooled states were estimated in all cases and found to lie in the range 10^–4–10^–6, thus constituting a small ‘bleed-off’ from the and Ca(¹D₂) energy stores without disturbing the observed first-order decay of these two states in the equilibrium-coupled system.