EPR studies of Cu
2+ and two free radicals formed by ¦Ã-radiation were performed for KHCO
3 single crystal at room temperature. From the rotational EPR results we concluded that Cu
2+ is chelated by two carbonate molecules in a square planar configuration with spin-Hamiltonian parameters
g|| = 2.2349 and
A|| = 18.2 mT. Free radicals were identified as neutral HOCO
with unpaired electron localized on the carbon atom and a radical anion with unpaired electron localized on two oxygen atoms. The hyperfine splitting of the EPR lines by an interaction with a single hydrogen atom of HOCO
was observed with isotropic coupling constants
ao = 0.31 mT. Two differently oriented radical sites were identified in the crystal unit cell. Electron spin-lattice relaxation measured by electron spin echo methods shows that both Cu
2+ and free radicals relax
via two-phonon Raman processes with almost the same relaxation rate. The temperature dependence of the relaxation rate 1/
T1 is well described with the effective Debye temperature
¦¨D = 175 K obtained from a fit to the Debye-type phonon spectrum. We calculated a more realistic Debye temperature value from available elastic constant values of the crystal as
¦¨D = 246 K. This
¦¨D-value and the Debye phonon spectrum approximation give a much worse fit to the experimental results. Possible contributions from a local mode or an optical mode are considered and it is suggested that the real phonon spectrum should be used for the relaxation data interpretation.
It is unusual that free radicals in KHCO3 relax similarly to the well localized Cu2+ ions, which suggests a small destruction of the host crystal lattice by the ionizing irradiation allowing well coupling between radical and lattice dynamics.