Electron Spin Resonance of Alkali Atoms in Inert-Gas Matrices

The electron spin resonance spectra of alkali atoms (Li, Na, K, Rb, Cs) trapped in inert-gas matrices (Ar, Kr, Xe) at liquid-helium temperature have been observed. The principal hyperfine structure for each alkali atom follows very closely the pattern prescribed by the known hyperfine constants. Around the position of each hyperfine component, there is in most cases a multiple line structure, which is shown experimentally to be associated with multiple trapping sites in the particular matrix. Values of $\frac{\Delta A}{A_0}$ and $\Delta g_J$, tabulated in all cases to describe the matrix effects on the spin resonance, are found to depend upon the nature of the trapping site as well as the character of the matrix.