Stationary points on the potential energy surfaces describing the reactions between Al and H 2 O, NH 3 , HCl, and Cl 2 respectively, have been optimized at the ab initio MP2 and QCISD levels as well as by density functional theory (DFT) using the B3LYP functional and the 6-31G(d,p) basis set. Reaction energies were computed using the MP2 and B3LYP methods and the QCISD and CCSD(T) methods in conjunction with the 6-311+G(2df,p) and 6-31G(d,p) bases, respectively. Isotropic hyperfine coupling constants (hfcc's) of Al, N, Cl, and H were computed using the MP2, B3LYP, and QCISD methods in conjunction with the 6-311+G(2df,p) basis, and at the PWP86/IGLO-III level for isotropic and anisotropic coupling constants. For HAlCl and AlCl 2 , the theoretical study predicts positive isotropic Cl hyperfine coupling constants at variance with the previously reported experimental values. A revised analysis of the experimental ESR spectra led to new assignments of the Cl hyperfine coupling tensors, in agreement with the computed results.

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Deuterium isotope effects on the methyl group conformation and ESR spectra of selectively deuterated dimethyl ether radical cations are demonstrated by employing experimental matrix-isolation ESR techniques in combination with accurate ab initio and density functional theory (DFT) quantum chemical methods. The experimental study shows strong deuterium isotope effects on the proton hyperfine coupling constants (HFCC) for CD 3 OCH 3 + , CD 3 OCH 2 D + , and CD 3 OCHD 2 + as well as a temperature dependence in the HFCC for CD 3 -OCH 2 D + and CD 3 OCHD 2 + . The deuterium isotope effects and temperature dependencies can be understood by incorporating the mass difference of the two hydrogen isotopes in addition to their magnetic properties, and utilizing new, improved quantum chemical structure calculations. Good agreement between experiment and theory is obtained when correlated ab initio (MP2) geometries are used in conjunction with DFT hyperfine coupling constants, whereas an erroneous temperature behavior is obtained for the HFCC when older methods or DFT calculations are used for the geometry determinations.