Excitation and ionization cross sections for He I from normalized born andK-matrix calculations: Delta S = 0 transitions from n = 2, 3 excited states

Two approximate methods, K-matrix (91 channels) and Normalized Born (13 cha nnels), are discussed and applied to the calculation of excitation cross se ctions and rate coefficients for transitions from excited states n = 2, 3 t o states with n' = 2, 3, 4 in He atoms. The ionization cross sections are a lso calculated by the Normalized Born method. Cross sections and rate coeff icients for transitions from n = 2 are compared with those obtained by the simple Born and the more sophisticated convergent close-coupling method. (C ) 2000 Academic Press.