Kinetic investigation of energy pooling from Sr [5s5p(3PJ)] studied by time-resolved atomic emission following pulsed dye-laser excitation

Abstract

A kinetic investigation is presented of energy pooling arising from self-annihilation of the optically metastable state, Sr[5s5p(³P_J)], generated by pulsed dye-laser excitation of strontium vapour at λ= 689.3 nm {Sr[5s5p(³P₁)]â†� Sr[5s²(¹S₀)]} at elevated temperature in the presence of excess helium buffer gas. Time-resolved emission was observed for a number of energy-pooled states, namely, Sr[5s5p(¹P₁)], Sr[5s6s(³S₁)], Sr[4d5p(³F_{2, 3, 4})], Sr[4d5p(¹D₂)], Sr[5s6p(³P_{1, 2})], Sr[5s5d(³D₂)] and Sr[5p²(³P₂)]. This includes characterisation of the time profiles from specific spin–orbit states and significantly extends the range of atomic pooled states reported hitherto derived from the 5s5p(³P_J) energy store. Following rapid energy pooling, the profiles of the ‘pool’ and ‘store’ states are shown to be exponential in character and the first-order decay coefficients are found to be in the ratio of 2 ∶ 1 within experimental error. Further, using the appropriate sensitivity calibration of the optical system, the variation of the ratio of the integrated atomic emission intensities of the energy pooled states to that of the energy store itself were found to be linear and in accord with a mechanism for energy pooling in each case arising from ³P_J+³P_J self-annihilation. The normalised, integrated emission intensities of the energy-pooled states which involved population via endothermic processes from Sr(³P_J)+ Sr(³P_J) were determined and used to calculate the relative distributions of the energy-pooled states on collision. These were plotted semi-logarithmically as a function of the electronic state energy of the appropriate state and yielded a Boltzmann temperature higher than the ambient temperature employed, reflecting the role of atomic collisions with high kinetic energies on energy pooling.