Metastable Ions in the Mass Spectra of CD3CH3 and C2H6

The mass spectra of CD3CH3 and C2H6 were searched for metastable transitions using a mass spectrometer with high sensitivity. With a detection limit of about 3 × 10−8 of the total ionization, 54 metastable transitions in CD3CH3, and 19 in C2H6 were found. All of these were checked for possible collision‐induced contributions by admitting krypton to the analyzer tube. The CH3CD3 decompositions are classified as (a) C–C ruptures, (b) H2, HD, and D2 eliminations, and (c) loss of an H or D atom. The first category provides information about D–H scrambling. The rate constant for D–H scrambling prior to C–C rupture is 5 × 104 sec−1 for parent ions, but very much larger in fragment ions, with the possible exception of CH2CD2+. The second category gives information about the isotope effect between H2, HD, and D2 loss. Compared to the loss of H2, the elimination of HD is diminished about fivefold and that of D2 by a factor of about 150. In the parent ion much less (if any) D–H scrambling occurs prior to the HD eli...