A study of the reactions between Ba(1S) and N2O, O2, and CO2

Abstract

A kinetic study is presented of the reactions between Ba(1S) atoms and N2O, O2, and CO2 over an extended temperature range. Ba atoms were produced in an excess of each oxidant and He bath gas by the pulsed 2-photon (193.3 nm) dissociation of BaO, produced in situ by the reaction between Ba vapor and the oxidant, and then monitored by time-resolved laser induced fluorescence spectroscopy at λ=553.55 nm (Ba(61P−61S)). The following results were obtained (at the 2σ level of uncertainty): k(Ba+N2O, 242<T<850 K) =(2.99±0.14)×10−10 exp[−(5.7±0.17) kJmol−1/RT]; k(Ba+O2, 254<T<566 K) =(4.89±0.38)×10−10 exp[−(7.06±0.23) kJmol−1/RT]; k(Ba+CO2, 257<T<849 K)=(3.97±0.21)×10−10 exp[−(7.66±0.18) kJmol−1/RT] cm3 molecule−1 s−1. These results are in good agreement with recent molecular beam studies. In the case of Ba+N2O, two line-of-centers collision models are employed to demonstrate that the effect of vibrational excitation of N2O is to enhance the chemiluminescence quantum yield as well as the reaction cross section. Comparison with the chemiluminescence cross section for the reaction Ba+N2O →BaO(A1Σ+ and A′1Π ), obtained in a beam-scattering experiment, indicates a branching ratio of (18.3±6.7)% into these states.