Energy barriers to CD3,CT3 rotations

 Dear CCLers,
      Does anyone know of literature references or unpublished information re
 calculated or experimental values for energy rotation barriers for isotopi-
 cally-substituted methyl groups in molecules such as ethane (H3C-CH3 vs.
 H3C-CD3 vs. H3C-CT3), 1,2-dimethylbenzene, or perhaps other chemical
 species?  MOPAC is insensitive to such isotopic substitutions vis-a'-vis
 heats of formation.
      Thanks to all responders in advance.
 S. Shapiro
 Abt. orale Mikrobiol. allg. Immunol.
 Zahnaerztl. Inst. der Univ. ZH
 Plattenstr. 11
 CH-8028 Zuerich, Switzerland
 Internet: toukie - at -
 FAX-nr: ( ... +1) 261'56'83