Rovibrational distributions of CH(A 2Δ,B 2Σ−) produced in energy-transfer reactions from Ar(3P2), Kr(3P2), and Xe(3P2) atoms to CH3 radical

Abstract

Energy-transfer reactions from Ar(3P2), Kr(3P2), and Xe(3P2) to CH3 radical have been studied by observing emission spectra from excited fragments in the flowing afterglow. CH3 radicals were generated by the F+CH4 reaction. The CH(A 2Δ–X 2Πr:v′=0−2) and CH(B 2Σ−–X 2Πr:v′=0) emission systems were observed in the Ar(3P2) reaction, while only CH(A–X:v′=0,1) emission system was found in the Kr(3P2) and Xe(3P2) reactions. The nascent rovibrational distributions of CH(A:v′=0–2) were N0:N1:N2 =100(T0 =3400±400 K):28±5(T1 =1700±400 K):4±1(T2 =700±300 K) in the Ar(3P2) reaction and 100(T0 =1000±250 K):<5(T1 <800 K):0 in the Kr(3P2) and Xe(3P2) reactions. The rotational distribution of CH(B:v′=0) in the Ar(3P2) reaction was reproduced by a single Boltzmann temperature of 2800±300 K. The average fractions of total available energies channeled into vibration and rotation of CH(A,B) were less than 15% for all cases, suggesting that most of the available energies was deposited as relative translational energy of products and/or rovibrational energy of H2. The observed rovibrational distributions of CH(A) were colder than those predicted from statistical theories including and excluding the conservation of total angular momentum. The best agreement between the observed and statistical distributions was obtained for the mechanism giving CH(A,B) in two-body dissociation steps by assuming that 78–92% of the total available energy is released as kinetic energy in the first step, Rg(3P2)+CH3→CH*3+Rg, then the rest remains in the precursor CH*3 state as an internal energy.