ESR OF SMALL ALKALI CLUSTERS

Well resolved ESR spectra have been obtained for molecular clusters of Li, Na and K in argon and nitrogen matrices. A large (isotropic) hf splitting into seven groups of transitions shows that the unpaired electron is mainly is in character and is localized on two equivalent alkali atoms. A much smaller superhyperfine (shf) structure shows that the radical contains at least three additional equivalent or near equivalent atoms. There is no evidence for a spin state other than S=1/2. The measured parameters (argon matrices) are $ \begin{array}{cccccc} &&&&&\\ \hline \\[-8pt] & ^{g}0 & ^{a}1 & ^{\pm a}2 & ^{\rho}1 & ^{1\rho}2 \\\hline Li & 2.000(1) &37(1) &2.1(1) &0.26 &0.015 \\ Na &1.9994(1) &118.2(1) &6.7(1) &0.37 &0.021\\ K &2.0017(1) &30.5(1) &1.79(3) &0.37 &0.022\\ \hline \end{array} $ where $a_{1}$ and $a_{2}$ are hf constants (In Gauss) for the septet and superhyperfine splitting respectively, and $\rho_{1}, \rho_{2}$ are the corresponding isotopic spin populations. The ESR data show that the Na and K clusters are markedly similar in character but Li is quantitatively different. As of writing, the exact identity of the spectral carrier is unclear, but $M_{5}, M_{7}$ or $M_{9}$ seen most likely