An upper limit for the rate of association reactions is found by determining the probability of a decrease of the relative energy of two atoms below zero energy, under the influence of a third body. The relation of this approximate calculation to the rigorous solution of the problem is discussed in Section 2. The results are applied to the recombination of J atoms, measured by Rabinowitch and Wood. Numerically, the agreement is quite good; however, the calculated values are somewhat too low, which cannot be explained by an inaccuracy of the method. Reasons for the discrepancy other than the possible nonadiabatic character of the reaction are discussed.
Topics
Quantum chemical dynamics
REFERENCES
1.
Cf. for previous literature e.g.
M. G.
Evans
and M.
Polanyi
, Trans. Faraday Soc.
31
, 876
(1935
).2.
The possibility of chemical reactions without quantum jumps in the state of the electronic system has been first realized by F. London, Sommerfeld Festschrift (S. Hirzel, 1928), p. 104.
3.
Cf. for a closer discussion of these conditions, E. Wigner, Trans. Faraday Soc. (1937).
4.
H.
Eyring
, J. Chem. Phys.
3
, 107
(1935
); M. G. Evans and M. Polanyi (reference 1).5.
The first complete outline of the theory has been given in R. Tolman’s Statistical Mechanics (Chemical Catalog Co., 1927).
Cf. also K. F. Herzfeld, Kinetische Theorie der Wärme (Müller‐Pouillet’s Handbuch der Physik, second edition, 1925).
6.
7.
This does not preclude the possibility of calculating the absolute rate of (1) more accurately than can be done in practice for reactions with activation energy. Although the transition state method should give nearly exact results for the latter, the parameters of the energy surface enter in such a critical way into the formulas that a calculation of the whole rate is hardly feasible at present. Cf. also reference 3.
8.
The second section serves only to establish the connection between the (impracticable) exact calculation of the rate and the approximate calculation of the ensuing sections.
9.
10.
Cf. for the spectroscopic data, H. Sponer, Molekülspektren (Berlin, 1936), Vol. I, p. 18.
11.
Cf. Landolt‐Börnstein’s Tables, 1st Ergänzungsband, p. 69. The radius of Xe, i.e., 1.75A, was used for J.
12.
In addition to this, the formation of an intermediate iodide of the third body may be considered. Cf. reference 9.
13.
For a discussion of this and related questions, cf. reference 10, Vol. 2, p. 103 f.
14.
15.
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© 1937 American Institute of Physics.
1937
American Institute of Physics
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