Cancellation effects in alkalilike doublet lifetimes

Abstract

A recent lifetime measurement of the 7p levels in Pb IV yielded an anomalous ratio [Formula: see text]. This result is shown to be a consequence of a nearly complete cancellation in the 6s–7p radial transition moment of the 2P1/2 level, coupled with the influence of wavelength-cubed factors on the 7s–7p, 6d–7p, and 6s2–7p transition probabilities. Cancellation effects that suppress the intensity of one branch of the decay of a level are a common feature of Δn > 0 transitions in alkali sequences, but this measurement demonstrates that these effects can also produce strong lifetime anomalies. The cancellation effects that produce this specific lifetime anomaly are examined isoelectronically, and the use of lifetime measurements near such cancellations as a probe of secondary interactions is discussed.