Electron Spin Resonance Studies of Alkali Metal Trapping Sites in Solid Rare Gases

Measurements of the hyperfine structure of alkali metals trapped in solid rare gases have been made. When the zero-field hyperfine splitting values obtained in the solid matrix are compared with the free atomic values, it is found that they fall into two groups. In one group the hyperfine values are within a few percent of the free atomic value. The other group has hyperfine values smaller than the free atomic value by 10 to 30%. It has been found that the latter trapping sites occur only when the sample is exposed to room temperature infrared radiation during deposition on the liquid helium cooled finger. The effects of annealing and concentration have also been studied. The annealing experiments show that once the shifted sites are formed they are very stable.