Bath Gas Mixture Effects on Multichannel Reactions: Insights and Representations for Systems beyond Single-Channel Reactions

Nearly
all studies of and available data for pressure-dependent
reactions focus on pure bath gases. Of the comparatively fewer studies
on bath gas mixtures, important to combustion and planetary atmospheres,
nearly all focus on single-channel reactions. The present study explores,
and seeks reliable representations of, bath gas mixture effects on
multichannel reactions. Analytical and numerical solutions of the
master equation here reveal several unique manifestations of mixture
effects for multichannel reactions, including behavior completely
opposite to trends observed for single-channel reactions. The most
common way of evaluating mixture rate constants from data for pure
components, the classic linear mixture rule, is found to yield errors
exceeding a factor of ∼10. A new linear mixture rule based
on the reduced pressure, instead of the absolute pressure, is found
to be accurate within ∼30% for rate constants (and ∼50%
for the branching ratio). A new nonlinear mixture rule that additionally
incorporates analytically derived activity coefficients is found to
be accurate within ∼10% for rate constants and branching ratios.
These new mixture rules are therefore recommended for use in fundamental
and applied chemical kinetics investigations of reacting mixtures,
including reacting flow codes and experimental interpretations of
third-body efficiencies.