RADIATIVE LIFETIMES AND COLLISION PROCESSES IN SODIUM-RARE GAS AND SODIUM-HYDROGEN SYSTEMS

Investigations of the collisional interactions between sodium atoms in the 3(2)P states and helium and hydrogen gases are described. Studies of collision-induced mixing and quenching interactions have been carr ied out under conditions where chemical reaction to produce sodium hyd ride is possible. Thus the sodium number derivatives are sufficient fo r radiation trapping to occur. This is in contrast to virtually all pr evious investigations in which conditions were such that this effect n eed not be considered. The intensity and temporal behaviour of laser i nduced fluorescence (LIF) resulting from the photoexcitation of the so dium 3(2)P states is monitored as a function of foreign gas pressure. Whilst many of the features observed are to be expected, results show how radiation trapping strongly influences cross-section determination . The need for a more rigorous treatment of collision cross-sections u nder these conditions, which are often more realistic than the 'ideal' trapping free situations, is demonstrated.