Effect of orthogonalization on total ionization cross sections by electron impact: application to small molecules

Total ionization cross sections by electron impact are calculated for H2O, NH3 and CH4 molecules by using an improved first Born approximation which has been previously applied for atomic targets by Bartlett and Stelbovics [P.L. Bartlett, A.T. Stelbovics, Phys. Rev. A 66, 012707 (2002)]. In this model a full orthogonalization of the final state to the initial state has been performed to evaluate the cross sections. One center wave functions are employed to describe the molecular orbitals. It is shown that the results obtained in the present model are immensely improved when compared with the first Born model without orthogonalization. Furthermore, an overall agreement is also observed when a comparison is made with the experimental data