Radiative lifetimes of quartet fine-structure states in the Ar II 3p⁴4p configuration

Precise lifetimes of three fine-structure levels in the 3p 4 4p configuration of the Ar + ion have been measured by means of the cascade-free technique of beam-dye-laser spectroscopy. The resulting lifetimes for the quartet levels 4p 4 P 5 2/ 0 , 4p 4 D 5 2/ 0 and 4p 4 D 7 2/ 0 are (7.36+or-0.03), (7.54+or-0.04) and (6.92+or-0.03) ns, respectively, where the uncertainties quoted correspond to one standard deviation. In view of the high level of experimental accuracy attained, a discussion of recent theoretical and experimental results found in the literature enables one to characterise the various methods used.