Low-energy electron excitation of the3Pefine-structure levels in atomic oxygen

Fine-structure collision strengths are calculated for transitions between the ground-state levels of atomic oxygen, 3 P e 2 , 3 P e 1 and 3 P e 0 , and comparisons are made with other calculations. The R-matrix method is used in which the (2p 4 ) 3 P, 1 D and 1 S terms are included as well as three pseudostates, 3 S o , 3 P o , and 3 D o , chosen to represent the dipole polarisability of the 3 P ground state. Configuration interaction wavefunctions are used for the target states. A recoupling transformation to pair coupling is applied to the inner-region Hamiltonian matrix, and before diagonalisation the 3 P fine-structure energy levels are adjusted to match the observed splitting. Thus the kinematics of the continuum electron are correctly accounted for. The threshold behaviour of the fine-structure collision strength for oxygen is established for the first time. By integrating the collision strength over a Maxwellian distribution, effective collision strengths are calculated for electron temperatures in the range from 10000 down to 50 K.