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 isotopes confined in silasesquioxane (R<INF>8</INF>Si<INF>8</INF>O<INF>12</INF>) cages show significant deviations from the free-particle vacuum value thus revealing the influence of the environment on the wave function of the trapped atom. Accurate measurements of the hfc constants in the temperature range of 5−300 K show a strong isotope effect, different substituents on the cage corners having a clear influence on both static and dynamic cage effects. Deviations of g-factors from the free-electron value are independent of temperature, but they depend on substituents. To gain information about the factors influencing the trapped atoms' dynamic behavior inside the cage environments, a phenomenological model developed previously for the description of the dynamics of hydrogen isotopes in liquid water and ice (J. Chem. Phys. <BO>1995</BO>, 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 understanding of matrix effects on the dynamics of particles in a constraining environment, a problem which represents a challenge for both phenomenological modeling and quantum chemical calculations.