Matrix Effects on the Electron Spin Resonance Spectra of Trapped Hydrogen Atoms

A study is made of the matrix effects on the electron spin resonance (ESR) spectra of hydrogen atoms stabilized in nonpolar matrices. It is assumed that the perturbing effect of the matrix consists of van der Waals interactions and the overlap or Pauli exclusion forces. These two effects are treated separately and the results added to get the net result. The van der Waals effect, which is treated by perturbation theory, leads to a reduction in the hfs splitting. The overlap effect, which is treated by requiring that the hydrogen atom wave function be orthogonal to the wave functions of the matrix particles, leads to an increase in the hfs splitting. In addition, the exclusion effect tends to introduce a small amount of the unpaired electron charge density onto the matrix particles. This can lead to a change in the electronic g factor, and also to hyperfine interactions with the nuclei of the matrix particles. The theory gives a good qualitative picture of the various matrix effects and their dependence on various properties of the matrix atoms and molecules.