Excitation of the 23S metastable state of helium by electrons

A systematic calculation for the total and differential cross sections for electron impact excitation of helium from its initially excited metastable 23S state to higher states namely n1.3S and n1.3P (with n=2-4) states is reported. Distorted wave approximation theory has been used for the calculation. The effect of different distortion potentials as well as the effect of target polarization by the projectile is explicitly considered. For comparison similar first Born level results are also calculated. Results are compared with the available earlier calculations and experimental data.