Interference in the Collective Electron Momentum in Double Photoionization of ${\mathrm{H}}_2$

We investigate single-photon double ionization of ${\mathrm{H}}_2$ by 130 to 240 eV circularly polarized photons. We find a double slitlike interference pattern in the sum momentum of both electrons in the molecular frame which survives integration over all other degrees of freedom. The difference momentum and the individual electron momentum distributions do not show such a robust interference pattern. We show that this interference results from a non-Heitler-London fraction of the ${\mathrm{H}}_2$ ground state where both electrons are at the same atomic center.

Figure 1

Double photoionization of ${\mathrm{H}}_2$ by 160 eV circular polarized photons. (a) Horizontal axis: angle between $k_1$ and the molecular axis in the polarization plane, vertical axis: $|k_1|$. $k_1$ and the molecular axis are each within $\pm 20°$ of the polarization plane; there is no restriction on $k_2$. (b) Polar presentation of data of (a) integrated over $|k_1|$. (c) Same for $2.75\mathrm{a}.\mathrm{u}.<|k_1|<2.81\mathrm{a}.\mathrm{u}.$. (d) Same for $2\mathrm{a}.\mathrm{u}.<|k_1|<2.7\mathrm{a}.\mathrm{u}.$. (e) Horizontal axis: angle between $k^{+}$ and the molecular axis in the polarization plane, vertical axis: $|k^{+}|$. $k^{+}$ and molecular axis are each within $\pm 20°$ of the polarization plane; the data are integrated over all other observables. (f) Polar presentation of data of (e) integrated over $|k^{+}|$. (g) Same for $3.1\mathrm{a}.\mathrm{u}.<|k^{+}|<3.9\mathrm{a}.\mathrm{u}.$. (h) Same for $2.3\mathrm{a}.\mathrm{u}.<|k^{+}|<2.6\mathrm{a}.\mathrm{u}.$. (i) Horizontal axis: angle between $k^{-}$ and the molecular axis in the polarization plane, vertical axis: $|2k^{-}|$. $k^{-}$ and molecular axis are each within $\pm 20°$ of the polarization plane; the data are integrated over all other observables. (j) Polar presentation of data of (i) integrated over $|2k^{-}|$. (k) Same for $3.5\mathrm{a}.\mathrm{u}.<|2k^{-}|<3.8\mathrm{a}.\mathrm{u}.$ (l) Same for $2.2\mathrm{a}.\mathrm{u}.<|2k^{-}|<2.5\mathrm{a}.\mathrm{u}.$.

Figure 2

Four different interfering breakup channels contributing to double electron ejection from ${\mathrm{H}}_2$; see text and Eq. (1).

Figure 3

Angular distribution of $k^{+}$ (left column) and $k^{-}$ (right column), for different photon energies as given in the figure. Photon propagation into the plane of the figure, molecular axis, and $k^{+}$ or $k^{-}$ are restricted to be within $\pm 20°$ of the polarization plane. It is integrated over the magnitude of $k^{+}$ and $2k^{-}$ and over all other observables.