THEORETICAL-STUDY OF DEUTERATED ETHANE CATIONS

Equilibrium and transition-state geometries, torsional barriers, and relative abundances at 4.2 and 77 K of different rotational isomers of deuterated ethane cations have been calculated, using ab initio MP2/6-31G** and MP4(SDTQ)/6-31G** theories. The relative abundances of rotationally related isomers, predicted from Boltzmann statistics based on differences in zero-point vibrational energies (ZPE), are in good agreement with low-temperature matrix isolation ESR data. The rotational barrier in the singly deuterated cation is calculated to be 0.11 kcal/mol higher than in the undeuterated ion, in reasonable agreement with the experimentally estimated difference of >0.25 kcal/mol.