J. Butler, T. Baer, S. Evans
Jun 11, 1983
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0
Influential Citations
37
Citations
Journal
Journal of the American Chemical Society
Abstract
The photoionization of dimethyl disulfide (CH/sub 3/SSCH/sub 3/) yields seven fragment ions between 10.0 and 10.7 eV. Among these are CH/sub 3/SS/sup +/ and C/sub 2/H/sub 5/S/sup +/ whose respective measured heats of formation, ..delta..H/sub f//sup 0//sub 298/, of 891 and 803 kJ/mol are significantly lower than previously reported. The rate of parent ion dissociation between 10.6 and 10.9 eV forming C/sub 2/H/sub 5/S/sup +/ and H/sub 2/CS/sup +/ was measured by photoelectron photoion coincidence. Comparison of the experimental rates with statistically expected rates leads to the conclusion that the dimethyl disulfide ion, which is initially produced with a CSSC dihedral angle of 90/sup 0/, rearranges to the more stable 180/sup 0/ dihedral angle geometry prior to dissociation. The statistical theory rates fit the measured rates when a 298 K heat of formation of 690 kJ/mol is assumed for the energy of the dimethyl disulfide ion in its lowest energy state. This is 87 kJ/mol lower than previously assumed on the basis of the adiabatic ionization energy. The dimethyl disulfide ion is, therefore, 154 kJ/mol more stable with a CSSC dihedral angle of 180/sup 0/ than with an angle of 90/sup 0/.