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Simulation and interpretation of vibrational isotope effects

Thesis/Dissertation ·
OSTI ID:6061497
The contributions of the individual coordinates to the reduced partition function (s/sub 2//s/sub 1/)f, values and to isotope effects on equilibrium constants are presented. The reduced isotopic partition function ratios (s/sub 2//s/sub 1/)f(/sup 13/C//sup 12/C) are dissected by perturbation theory for a series of alkanes. It is shown that the major contribution of the P factors (perturbation correction) can be included with the c factors (unperturbed correction) to form the c' factor and that these very well characterized P factors are necessary to approximate (s/sub 2//s/sub 1/)f. Moreover, the c' and P factors corresponding to given types of coordinates are similar so that it is suggested that all the alkanes (s/sub 2//s/sub 1/)f(/sup 13/C//sup 12/C) values can be estimated from a table of average c' and P factors. In studies with H isotopes, it is found that an extremely good correlation exists between (s/sub 2//s/sub 1/)f(H/Mu), (s/sub 2//s/sub 1/)(D/H), and (s/sub 2//s/sub 1/)f(T/H) values. H/sub eq/ for an H/Mu isotopic exchange reaction is estimated by an interpolative method which utilizes this correlation and a zeroth order perturbation method. However, when these two methods are combined, it is suggested that more reliable estimates for K/sub eq/(H/Mu) can be obtained. In an equilibrium fractionation process the (/sup 18/O//sup 16/O) ratio in one of the chemical species involved should be increased by 1.88% if the (/sup 17/O//sup 16/O) ratio in the same species is increased by 1%. If certain conditions are met, equilibrium fractionation alone would explain the distribution of O isotopes in various terrestrial and lunar samples that were determined by Clayton and coworkers. (BLM)
Research Organization:
California Univ., Irvine (USA)
OSTI ID:
6061497
Country of Publication:
United States
Language:
English