Translational exoergicity

Despite the large exoergicity, less than about 100 kJ mol-1 appears as HC1 translation, rotation or vibration. On average, 60kJmol-1 appears as HC1 translation, 30 kJ mol-1 appears as HC1 vibration (peaks at v = 1) and 10 k.l mol 1 as rotation.39 It was argued in Ref. 39 that despite possessing similar energetics, the Eley-Rideal reaction is qualitatively different than the gas-phase reaction ... 

Several examples of exoergic charge-transfer reactions that proceed at different rates with ground-state and electronically excited ions are listed in Table I. In some cases the cross section for the excited-state reaction may be smaller than that for the ground state, as is the case for the reactions Xe+(02, Xe)02+ Kr+(N20, Kr)N20+ Kr + (C02, Kr)COz+, whereas in other instances the excited state is more reactive, as for the processes N+(Kr,N)Kr+, N+(CO,N)CO+, 02+(Na,02)Na and 0/ (NO, 02)N0 +. The differences in reactivity are often more pronounced in the region of low ion translational energies1 lb (Fig. 10). The role of excited-state ions in charge-transfer reactions was reviewed by Hasted some time ago,175 but much more experimental data has been obtained recently, as indicated by the data shown in Table I. 

Luminescence spectra resulting from pure vibrational or V-R transitions involving excited-product states formed in ion-neutral collisions have not yet been observed. However, vibrational and rotational excitation of the products of reactive ion-neutral collisions may be determined indirectly from measurements of Q, the translational exoergicity, which is defined as the difference between the translational energy of the products and that of the reactants. According to the energy-conservation principle, then,... 

The electronic quenching process (eq. 13) may occur through an exoergic electronic-to-electronic (E-E) energy transfer, an electronic-to-vibrational (E-V) energy transfer, an electronic-to-rotation (E-R) transfer, an electronic-to-translation (E-T) transfer, or a chemical reaction. Studies of E-E transfer,... 

The use of laser-induced fluorescence as a molecular beam detector for the measurement of internal state distributions of reaction products is presented and applied to the reactions of barium with the hydrogen halides. It is found that most of the reaction exoergicity appears as translational energy of the products and that the total reactive cross section is positively correlated with the average fraction of the exoergicity appearing as vibrational excitation. 

Table 4 summarizes the results for these reactions, where Ey and r denote the average BaX vibrational and rotational energies and /v,/r and denote the fractions of the total reaction exoergicity that appear as vibration, rotation and translation, respectively. The Ba+HX reactions are characterised by little vibrational and rotational excitation of the products, and there is a positive correlation of fy with cross section for the reaction Ba+DCl is only 60 % of that for Ba+HCl. A similar result has been obtained for the K+HBr and K+DBr reactions. ... 

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