Cycloheptatriene ions, decomposition

D > thfi source reaction following El has been found to fall from 8 at threshold to 1.4 at 20 eV. It was pointed out that 1.4 corresponds to the ratio of the C—H and C—D stretching frequencies, i.e. the high energy limit may have been reached. The isotope effect, /h//d. on hydrogen atom loss from cycloheptatriene has been given as 1.49 for the El source reaction and 2.6 for metastable ion decompositions [435]. 

Howe, I. McLafferty, F.W. Unimolecular Decomposition of Toluene and Cycloheptatriene Molecular Ions. Variation of the Degree of Scrambling and Isotope Effect With Internal Energy. J. Am. Chem. Soc. 1971, 9J, 99-105. 

---