Electronic excitation of H2O by positron impact

The electronic excitation of H2O molecule by positron impact for the (1b(1)-> 4a(1))B-1(1) and (3a(1)-> 4a(1))(1)A(1) transitions has been calculated from threshold to 60 eV. The calculations were performed with the Schwinger multichannel method considering two and three channel-coupling schemes. We have found that the electronic excitation cross sections induced by positron impact show negligible dependence with the number of collision channels taken into account and seem to be always smaller or at most of the same magnitude than the corresponding ones for electrons using similar representations for the target excited states. The calculated cross sections exhibit lower magnitude when compared to the experimental data of Tattersall et al. [W. Tattersall, L. Chiari, J.R. Machacek, E. Anderson, R.D.White, M.J. Brunger, S.J. Buckman, G. Garcia, F. Blancoand J.P. Sullivan, J. Chem. Phys. 140, 044320 (2014)], while showing good agreement with the excitation cross sections recommended by Blanco et al. [F. Blanco, A.M. Roldan, K. Krupa, R.P. McEachran, R.D. White, S. Marjanovic, Z. Lj. Petrovic, M.J. Brunger, J.R. Machacek, S.J. Buckman, J.P. Sullivan, L. Chiari, P. Limao-Vieira, G. Garcia, J. Phys. B: At. Mol. Opt. Phys. 49, 145001 (2016)] for energies above 30 eV. Perspectives to go beyond this prelusive investigation on positron-H2O electronic excitation, such as inclusion of target polarization effects, are discussed.