Theoretical and electron spin resonance studies of the the Hâ â â H, Hâ â â D, and Dâ â â D spin-pair radicals in rare gas matrices: A case of extreme singlet-triplet mixing
Knight, L. B.; Rice, W. E.; Moore, L.; Davidson, E. R.; Dailey, R. S. Theoretical and electron spin resonance studies of the the Hâ â â H, Hâ â â D, and Dâ â â D spin-pair radicals in rare gas matrices: A case of extreme singlet-triplet mixing. J. Chem. Phys. 1998, 109, 1409-1409.
The Hâ‹¯H, Hâ‹¯D, and Dâ‹¯D spin-pair radicals have been thoroughly investigated in neon, argon, krypton, and xenon matrices near 4 K by electron spin resonance(ESR). A theoretical model has been developed that treats these spin-pairs as weakly interacting atoms. The model includes the effects of 3 Î£/ 1 Î£ mixing in the analysis of the observed ESR spectral results and yields a consistent set of magnetic parameters for these three isotopomers in all four rare gas hosts. The consideration of H atoms interacting with other H atoms over a distribution of internuclear distances in the rare gas lattice is included in the theoretical and experimental analyses. Application of the model to earlier ESR results for Hâ‹¯CH 3 reveals a value for its Heisenberg exchange interaction (J) which is found to be considerably larger than that for the Hâ‹¯H spin-pair. The effects of methane and neon on the J value are calculated for these spin-pairs. The Hâ‹¯H case is unusual in that the nuclear hyperfineinteraction (A) is considerably larger than D (the anisotropic dipoleâ€“dipole magnetic interaction between electrons) which is much larger than J. The Hâ‹¯H spin-pairs exhibit internuclear distances greater than 7 Ã… and have the following magnetic parameters (MHz) based upon this model of â€œweakly interacting atoms;â€ g iso =2.0016, A iso =1426, D=âˆ’200, and J=6. Since a distribution of distances is involved, other spin-pairs would be separated by even greater distances in the matrix and thus have smaller absolute values of D and J.
Journal of Chemical Physics