Experimental and theoretical study of thenf-level lifetimes of potassium

Abstract

The theoretical and experimental values of the 5f, 6f, 7f, and 8f radiative lifetimes of neutral potassium are reported. The reduced matrix elements for all allowed electric-dipole nf 5/2 -nЈd 5/2 , nf 5/2 -nЈd 3/2 , and nf 7/2 -nЈd 5/2 transitions with n =5-8 in K are 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 and their uncertainties. The contributions from the nf 5/2 -nЈg 7/2 , nf 7/2 -nЈg 7/2 , and nf 7/2 -nЈg 9/2 transitions to the lifetimes of the 6f, 7f, and 8f states are evaluated using the third-order manybody perturbation theory and are found to be very small. The theoretical results are 5f = 117͑4͒ ns, 6f = 195͑4͒ ns, 7f = 301͑6͒ ns, and 8f = 441͑9͒ ns. The experiment is performed in a cell using time-resolved fluorescence spectroscopy. The nf states are excited stepwise, 4s → 4p → nf, using two pulsed synchronous dye lasers for the dipole and quadrupole transitions, respectively. The measured values 5f = 117͑3͒ ns, 6f = 190͑6͒ ns, 7f = 309͑8͒ ns, and 8f = 428͑10͒ ns are in excellent agreement with the present theoretical calculations.

Energy transfer reaction K(4s) + K(7s) → K(4s) + K(5f), theory compared with experiment

“…Past the peak, the I 7s signal stabilized to a single exponential dependence. Values for f Γ 5 were taken from our other experiment [26]. Please note, that to both of these measured ("effective") decay rates i Γ , besides the spontaneous-emission rate (inverse of state's natural lifetime), two other components additively contributed.…”