ESR spectra of matrix isolated potassium atom clusters

Abstract

ESRspectra assigned to the previously unobserved 39K3 molecule have been obtained by co‐depositing atomic potassium with argon under conditions favorable to cluster formation. The ESRspectra 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 2 B 2. 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. K3spectra 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.