Lifetimes of the 5f, 6f, 7f, and 8f states of potassium have been studied both theoreticaly and experimentally. The reduced matrix elements for all allowed electric-dipole nf5/2-n'd5/2, nf5/2-n'd3/2, and nf7/2-n'd5/2 transitions with n=5-8 in K were calculated using the relativistic linearized coupled-cluster method with single and double excitations of Dirac-Fock wave functions included to all orders in many-body perturbation theory. The resulting electric-dipole matrix elements are used to evaluate the lifetimes of the 5f, 6f, 7f, and 8f states in neutral K. The contributions from the nf5/2-n'g7/2, nf7/2-n'g7/2, and nf7/2-n'g9/2 transitions to the lifetimes of the 6f, 7f, and 8f states were evaluated using the third-order many-body perturbation theory and were found to be very small. The theoretical results are
τ5f =117.4 ns;
τ6f =195.4 ns;
τ7f =301.6 ns;
τ8f =441.9 ns.
The experimental values were obtained form an experiment in a vapour cell using time-resolved fluorescence measurements upon pulsed two-step excitation scheme 4s→4p→nf. The measured values
τ5f =117.3 ns;
τ6f =190.6 ns;
τ7f =309.8 ns;
τ8f =428.1 ns
are in excellent agreement with the present theoretical calculations. The results are published in . Collisional quenching cross-sections of the nf states with n = 5-8 were also measured as (in units of 10-13 cm2) σq = 2.4±1.7; 4.5±1.4; 8.1±1.8, 18.2±3.0, respectively .
 M. Głódź, A. Huzandrov, M. S. Safronova, I. Sydoryk, J. Szonert, and J. Klavins, Phys. Rev. A 77, 022503 (2008);
 M. Głódź, A. Huzandrov, I. Sydoryk, J. Szonert, and J. Klavins, Acta Phys. Pol. A 112, 1185 (2007).