Rovibrational distributions of CH(A 2Δ) produced in energy-transfer reactions from Ar(3P2), Kr(3P2), and Xe(3P2) atoms to C2H5 radical

Abstract

The CH(A 2Δ–X 2Π) emission system from v′=0 was observed in energy-transfer reactions from the metastable Ar(3P2), Kr(3P2), and Xe(3P2) atoms to C2H5 radical in the flowing afterglow. The nascent rotational distributions of CH(A:v′=0) were represented by an effective Boltzmann temperature of about 1000 K for all three reactions. The average fractions of total available energies channeled into rovibrational modes of CH(A) were less than 8.4%, suggesting that most of available energies were deposited as relative translational energy of products and/or rovibrational energy of CH4. The observed rovibrational distributions for the Ar(3P2) and Kr(3P2) reactions were colder than those predicted from a simple statistical theory. The best agreement between the observed and statistical rovibrational distributions was obtained in two-body dissociation [C2H*5→CH(A)+CH4] mechanism assuming that the energy transfer takes place with significant momentum transfer, leaving long-lived C2H*5 at ∼8.2 eV, in which energy randomization is complete before dissociation. For the Xe(3P2) reaction, the observed rovibrational distributions were in good agreement with the statistical ones obtained in two-body and three-body dissociation [XeC2H*5→CH(A)+CH4+Xe] models without taking account of momentum transfer. It was therefore concluded that CH(A) is formed through near resonant energy transfer, leaving long-lived C2H*5 and/or XeC2H*5 intermediates.