Using the time-resolved laser-induced fluorescence (LIF) technique in a tin atomic beam, 40 natural radiative lifetimes have been measured for the even-parity J = 1 5 pnp (n = 10-13, 15-19) and J = 2 5 pnp (n = 10-13, 15-19, 27, 31, 32), 5pnf (n = 4, 5, 9-19, 22, 23) levels along the Rydberg series and for all the 5p8p perturbing levels of neutral tin with energies in the range 52263.8 to 59099.9 cm-1. A two-step laser excitation scheme was used in the experiment. A multiconfigurational relativistic Hartree-Fock (HFR) calculation taking core-polarization effects into account has also been performed for the even-parity states for testing the ability of this approach to correctly predict the radiative properties of tin atom. Through an analysis of the energy levels structure by the multichannel quantum defect theory (MQDT), the channel admixture coefficients have been obtained and used to fit the theoretical lifetimes to the experimental ones in order to predict new values for the levels not measured. A generally good overall agreement between experimental and theoretical MQDT and HFR lifetimes has been achieved except for a few levels.
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