SIMBAD references

Experimental cross sections are reported for the 1s²2s²¹S⟶1s²2s2p¹P° transition in O⁺⁴ located at 19.689 eV. Use is made of the electron energy-loss method, using a merged electron-ion beam geometry. The center-of-mass interaction energies for the measurements in the ¹S⟶¹P° transition are in the range 18 eV (below the threshold) to 30 eV. Data are compared with other previous electron energy-loss measurements and with results of a 26 term R-matrix calculation that includes fine structure explicitly via the Breit-Pauli Hamiltonian. Clear resonance enhancement is observed in all experimental and theoretical results near the threshold for this ¹S⟶¹P° transition.