The Two-Photon Detachment Cross Section of Ps^-

For energies below the Ps(n=2) threshold, we computed the two-photon detachment cross-section of Ps^- into both a ¹S and ¹D final state [1]. We considered both the length and velocity forms of the cross section. To determine the ¹S and ¹D final-state continuum wave functions we employed the complex Kohn variational method whereas to determine the ¹S bound-state wave function we employed the Rayleigh-Ritz variational method [2]. For the ¹P intermediate-state wave function we solved an inhomogeneous differential equation resulting from the application of the Dalgarno-Lewis procedure [3]. Our cross-section results agree well with those of Igarashi [4,5] who used the close-coupling method but differ from the results of Maniadaki et al. [6] who used the configuration method. We showed that near threshold the Ps^- single photodetachment cross section and the two-photon detachment cross section satisfy Wigner’s threshold law [7] and a modified Wigner’s threshold law [8].

[1] W. Mitchell and S.J. Ward, Submitted (2025).

[2] W. Mitchell and S.J. Ward, J. Phys. B 58, 075203 (2025)

[3] A. Dalgarno and J.T. Lewis, Proc. R. Soc. A 233, 70 (1955).

[4] A. Igarashi, J. Phys. B 45, 245201 (2012).

[5] A. Igarashi, Few-Body Syst. 54 1561 (2013).

[6] K. Maniadaki, L.A.A. Nikolopoulos and P. Lambropoulos, Eur. Phys. J. D 20, 205 (2002)

[7] E. P. Wigner, Phys. Rev. 73, 1002 (1948)

[8] J. W. Farley, Phys. Rev. A, 40, 6286 (1989)