A 29-STATE R-MATRIX CALCULATION OF ELECTRON PHOTON COINCIDENCE PARAMETERS LAMBDA AND CHI FOR THE ELECTRON-EXCITATION OF 1(1)S-2(1)P IN HELIUM AT LOW ENERGIES

The R-matrix method has been employed to study the electron excitation of atomic helium. Twenty-nine target states (n = 1, 2, 3, 4 and 5) have been included in the expansion of the total wavefunction. The results of the calculation are used to obtain the electron-photon coincidence parameters lambda and chi for the excitation 1(1)S-2(1)P at 500 energies ranging from the 2(1)P threshold to 24 eV. The calculated parameters lambda and chi are compared with values obtained from experiments and with earlier five-, 11- and 19-state R-matrix calculations.