Angular distribution of the characteristic line 1s2p3P2→1s21S0 of thallium ions: hyperfine-induced multipole interference.

Within the framework of the density matrix theory, the angular distribution of the characteristic magnetic-quadrupole line 1 s 2 p 3 P 2 → 1 s 2 1 S 0 following electron-impact excitation of heliumlike thallium ions with nuclear spin I = 1 / 2 has been investigated by using the multiconfigurational Dirac–Hartree–Fock method and the relativistic distorted-wave theory. Special attention has been paid to exploring the question of how the angular distribution of the characteristic line is affected by the multipole interference between the dominant magnetic-quadrupole and hyperfine-induced electric-dipole decay channels of its hyperfine-structure-resolved component 1 s 2 p 3 P 2 , F = 3 / 2 → 1 s 2 1 S 0 , F 0 = 1 / 2 . To this aim, detailed calculations are performed for spin-1/2 81 187 Tl 79 + and 81 207 Tl 79 + ions with (relatively) large nuclear magnetic dipole moment. It is found that the hyperfine-induced multipole interference contributes to making the angular distribution of the magnetic-quadrupole line 1 s 2 p 3 P 2 → 1 s 2 1 S 0 less anisotropic for all the impact electron energies considered, although at any given impact energy its angular emission pattern remains always qualitatively consistent with each other for both the two cases without and with the interference contribution included. Moreover, for the case with the interference considered the angular distribution of the magnetic-quadrupole line is found to be sensitive to the nuclear magnetic dipole moment of the spin-1/2 ions, especially at low impact electron energies. [ABSTRACT FROM AUTHOR]