Theory of relativistic magnetic dipole transitions: Lifetime of the metastable 2S3 state of the heliumlike ions

Gordon W. F. Drake, University of Windsor

copyright American Physical Society


It has recently been established that the radiative lifetime of the metastable 2S3 state of helium and the heliumlike ions is determined by single-photon magnetic dipole (M1) transitions to the ground state, rather than the two-photon process proposed by Breit and Teller. The theory of nl-n′l M1 transitions with n ′ is developed in the Pauli approximation and extended to two-electron systems. Terms arising from relativistic energy corrections and finite-wavelength effects are included. The results for hydrogenic systems are shown to be identical to those obtained in the relativistic four-component Dirac formulation. The coefficients in the Z-1 perturbation expansion of the 1s2sS3-1s2S1 M1 transition integral are evaluated through ninth order and used to calculate the M1 emission probabilities from the 2S3 state of the two-electron ions up to Fe XXV. The emission probability for neutral helium is 1.27 × 10-4 sec-1. The results are compared with recent solar coronal observations by Gabriel and Jordan, and with a measurement of the 2S3 state lifetime in Ar XVII by Schmieder and Marrus. © 1971 The American Physical Society.