Positron Impact Excitation of the 2S State of Atomic Hydrogen

Abstract

The excitation cross-sections of the 2S state of atomic hydrogen at low (near threshold energy) to high incident positron energies (10.30 to 300 eV) have been calculated using the variational polarized-orbital method. Nine partial waves have been used to obtain converged cross-sections in the above energy range. The cross sections compared to the electron-impact excitation of the S state of atomic hydrogen are larger in the present case. The maximum cross section is 3.63(−1) π a 0 2 at 16.5 eV compared to 1.37(−1) π a 0 2 at 11.14 eV for the electron-impact excitation. The present results are compared with other calculations. Cross-sections have also been calculated in the Born approximation in which the polarization of the target has been included. Differential cross sections were calculated at k = 1.0 (13.6eV), 2.5 (85 eV), 3.483 (200 3V), and 4.696 (300 eV).

Positron Impact Excitation of the nS States of Atomic Hydrogen

“…However, the agreement is quite good even at low-incident energies. A comparison of positron-impact excitation cross sections and electron-impact cross sections to the excited 2S is shown in Figure 3, which was given in the previous publication [7] and is repeated again because results at higher energies are not the same as before, as explained above. The positron-impact cross sections are higher than the electron-impact cross sections.…”

“…Wigner [12] has emphasized the importance of the long-range forces near the threshold region. The long-range force has been included in the present calculation, as indicated in [7,11]. In the threshold region the cross sections are proportional to 2 (ln( )) f k − [13].…”

“…Other quantities in Equation (3) are given in [7] and the parameter β in Equation (8) of [7] is generally equal to 0.5. The final state wave function for a partial wave L is given by:…”

“…Total cross sections calculated by him are the sum of elastic and excitation cross sections to all levels above n = 1. In a previous publication [7], results for positron-impact excitation cross sections for the excitation of the 2S state of atomic hydrogen were given for the incident positron energies (10.30 to 300 eV). It was shown that at high-incident energies cross sections are very close to those obtained using the Born approximation.…”

“…It was shown that at high-incident energies cross sections are very close to those obtained using the Born approximation. In that calculation [7], there was a misprint in the computer program for scattering, found recently, 2 of 7 affecting results for higher partial waves. For example, for k = 0.90 the cross section changes from previous value of 0.247 to 0.246, at k = 1.2 it changes from 0.338 to 0.317, and at the highest k = 4.696 it changes from 0.0128 to 0.0151.…”