ESR spectra of matrix isolated potassium atom clusters

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Abstract
ESR spectra assigned to the previously unobserved 39K3 molecule have been obtained by co-depositing atomic potassium with argon under conditions favorable to cluster formation. The ESR spectra show that the trimer is chemically bound, with predominantly s rather than p character. Approximately 95% of the 4s spin population resides equally on two 39K nuclei with less than 6% on the third atom. The trimer is assigned a symmetric linear or ’’obtuse angled’’ isosceles geometry with ground state symmetry 3Σ+u or 2B2. A second ESR spectrum, a pattern of 10 equally spaced hyperfine components centered close to the free electron g value, is indicative of a radical species containing three equivalent 39K nuclei each having an isotropic spin population of slightly less than 1/3. Plausible candidates for the carrier of this spectrum are K5 with a linear or ’’zig–zag’’ geometry, or a ’’pseudorotating’’ isomer of K3. ESR intensities show a pronounced temperature dependence. K3 spectra are significantly enhanced by warming to T∼19 K, but almost completely disappear at T∼25 K, where the 10 line spectrum is most intense.