Reaction rate constants afterglow

F. C. Fehsenfeld, A. L. Schmeltekopf, D. M. Dunkin, and E. E. Ferguson, Compilation of Reaction Rate Constants Measured in the ESSA Flowing Afterglow System to August, 1969, ESSA Technical Report ERL 135-AL3 (September 1969), U.S. Gov t. Priniting Office. 

The flowing afterglow technique for ion-molecule reaction rate constant measurements has been developed since 1963 in the NOAA laboratories in Boulder, Colorado by A. L. Schmeltekopf, F. C. Fehsenfeld, and the author. This technique has also been applied recently to ion-molecule reaction studies in the laboratories of H. I. Schiff at York University, Toronto, W. L. Fite and F. Kaufman at Pittsburgh University, N. D. Twiddy at York University, England, " and perhaps elsewhere, so that extended results from this technique are to be expected in the future. 

The flowing afterglow measurements of the + 2 02 + O reaction rate constant shown in Fig. 4 agree quite precisely with earlier results of Smith and Fouracre " over the 185-576°K range. The N2 + 2- 02 + N2 charge-transfer rate constant shown in Fig. 4 had been substantiated by work of Biondi s group in drift tubes in which the decrease of k is found to continue to N2 ion kinetic energies of 1 eV. 

Figure A3.5.5. Rate constants for the reaction of Ar with O2 as a fiinction of temperature. CRESU stands for the French translation of reaction kinetics at supersonic conditions, SIFT is selected ion flow tube, FA is flowing afterglow and HTFA is high temperature flowing afterglow.

In the present review, a new variation on an existing experimental method will be used to show how accurate unimolecular dissociation rate constants can be derived for thermal systems. For example, thermal bimolecular reactions are amenable to study by use of several, now well-known, techniques such as (Fourier transform) ion cyclotron resonance spectrometry (FTICR), flowing afterglow (FA), and high-pressure mass spectrometry (HPMS). In systems where a bimolecular reaction leads to products other than a simple association adduct, the bimolecular reaction can always be thought of as containing a unimolecular... 

The data shown in Table 2 indicate that association of the ion in the gas phase lowers significantly the rate constant of the SN2 reaction. An even better example of this behaviour can be seen in the recent experiments of Bohme and Mackay (1981). The use of flowing afterglow techniques, in a sample rich in water vapour, allowed the measurement of the rate constant for reaction (30) as a function of successive degrees of hydration. These... 

The electron attachment reactions for inorganic molecules were reviewed in 1974. Those for organic molecules were summarized in 1984 [12, 13]. In many cases activation energies were not measured. If a nominal value for A and A is assumed, the activation energies can be estimated. Recently, the flowing afterglow procedure has been extended to include electron and gas heating so that the dependence of the rate constants on thermal electron attachment can be examined for bulk temperature and electron temperature [14]. 

The rate constant of the red afterglow which arises from the reaction of atomic hydrogen, H( S), with BCI3 is A =46 s . An inverse predissociation mechanism is believed to be responsible, with a probable fast stage of reaction being ... 

Reaction Mechanisms in the Noble Gas Afleisfows.— The above survey of the electronic states of the noble gas molecules allows discussion of the kinetic data accumulated on the pure noble gas afterglows. These data comprise total quenching rate constants for excited atomic states, whidi are summarized in Table 3, and comparisons of the kinetics of atomic emissions with those of the first and second continua, from vdiich attempts have been made to elucidate the mechanisms for the formation of the emitting molecular states. 

We note again that the thermal rate constant so obtained may differ from that obtained from the flowing afterglow technique in the case of a fast reaction. For the latter case, the initial Maxwellian velocity distribution is maintained, whereas in the present case, it is not. In such a case, the plot of Is Ip against delay time would exhibit curvature and the equilibrium rate constant would come from the slope in the limit of zero delay time this effect has not been observed. 

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