A KINETIC-STUDY OF THE RECOMBINATION REACTION NA + SO2 + AR

The recombination of atomic sodium, Na(3(2)S), with SO2 has been investigated at 787 K, in a bath of Ar at pressures from 1.7 to 80 kPa. Na was generated by pulsed excimer laser photolysis of NaI vapor at 308 nm and monitored by time-resolved resonance absorption of the D lines at 589 nm under pseudo-first-order conditions. The measured pseudo bimolecular rate constants lie in the third-order and falloff regions and were fitted well by using either a Lindemann mechanism or an empirical RRKM expression. The parameters are discussed in the text. The low-pressure limit is about (2.4-2.7) X 10(-29) cm6 molecule-2 s-1. By use of RRKM theory, combined with a lower limit based on the absence of any observed equilibration, the Na-SO2 bond energy is estimated as 190 +/- 15 kJ mol-1. Extrapolation to the high-pressure limit yields k infinity almost-equal-to (1-3) X 10(-10) cm3 molecule-1 s-1, in accord with a harpoon model for electron transfer to form an ionic adduct.