The heterogeneous interaction of Br( 2 P 3/2 ) and Br( 2 P 1/2 ) with surfaces of Teflon™ and polycrystalline nickel

Pulses of Br( 2 P 3/2 ) and Br( 2 P 1/2 ) (=Brast;) have been exposed to Teflon (PTFE) and to polycrystalline Ni surfaces in a Knudsen cell. The Br and Br* atom densities have been measured as a function of time using [3 + 2] Resonance Enhanced Multiphoton Ionization (REMPI) at 461.9 and 459.1 nm, respectively, and an absolute calibration of the sum of the density of Br and Br* on Teflon at ambient temperature has been measured to result in identical values within experimental error for both Br and Br*, namely γ(Br) = (5.6 ± 1.5) · 10 −5 , if an appropriate correction for the radiative lifetime of Br* of 0.77 s −1 is applied. The uptake coefficients for Br and Br* on polycrystalline Ni seem to be identical: γ(Br) = γ(Br*) = (5.6 ± 1.8) · 10 −3 and independent of temperature in the range 295 to 500 K. A possible exception is the value for γ(Br*) of 2.3 · 10 −3 at T = 295 K which seems to be significantly lower than the remainder of the uptake data. In the temperature range 500 to 700 K the uptake coefficients for both Br and Br* can be expressed as\documentclass{article}\pagestyle{empty}\begin{document}$$ \gamma = 0.18 \cdot \,\exp ( - 3300/RT),\,R - 1.987\,{\rm cal}\,{\rm mol}^{{\rm - 1}} \,{\rm K}^{{\rm - 1}} $$\end{document} . The system has a small positive activation energy in the range 3.3 to 4.5 kcal/mol. Br* seems to be less reactive than Cl* with respect to surface deactivation on poly Ni by a factor of six. In analogy to Cl the present system is characterized by kinetic complications in conjunction with the reversible surface poisoning of bromine, both atomic and molecular, on surfaces of Teflon (PTFE) and poly Ni that leads to the decrease of Br and Br* uptake with increasing exposure. © 1995 John Wiley & Sons, Inc.