Electron paramagnetic resonance study of the dynamics of H and D atoms trapped in substituted silasesquioxane cages

The hyperfine coupling (hfc) constants, A, and the g-factors of hydrogen is otopes confined in silasesquioxane (R8Si8O12) cages show significant deviat ions from the free-particle vacuum value thus revealing the influence of th e environment on the wave function of the trapped atom. Accurate measuremen ts of the hfc constants in the temperature range of 5-300 K show a strong i sotope effect, different substituents on the cage corners having a clear in fluence on both static and dynamic cage effects. Deviations of g-factors fr om the free-electron value are independent of temperature, but they depend on substituents. To gain information about the factors influencing the trap ped atoms' dynamic behavior inside the cage environments, a phenomenologica l model developed previously for the description of the dynamics of hydroge n isotopes in liquid water and ice (J. Chem. Phys. 1995, 102, 5989), which is based on the spherical harmonic oscillator, is applied to the more rigid silasesquioxane cage systems. The present study aims at a better understan ding of matrix effects on the dynamics of particles in a constraining envir onment, a problem which represents a challenge for both phenomenological mo deling and quantum chemical calculations.