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The angular correlation functions (ACFs) of a pair of Lyman-a photons emitted from H fragments in the photodissociation of a hydrogen molecule are measured at a 33.66-eV incident photon energy and at hydrogen gas pressures of approximately 0.1 and 1 Pa. The ACFs are measured for both opposite and nonopposite arrangements of the two photon detectors. It turns out that the experimental ACFs involve neither the contribution of the reactions H(n = 2) + H2 nor the contribution of the cascade from H(n > 3) to H(2p ) fragments. Thus the experimental ACFs are those for primary H(2p) pairs following the photodissociation of H2. The experimental ACFs are compared with (i) the theoretical ACF for entangled pairs of H(2p) atoms, where the magnetic quantum number of each hydrogen atom is indefinite, and (ii) the theoretical ACF for H(2p) pairs with definite magnetic quantum number of each hydrogen atom relative to the internuclear axis [the former entangled state of H(2p) pairs is a sum of the latter pair states with definite magnetic quantum number]. In the theoretical ACF in (ii), the disentanglement in H(2p) pairs during the dissociation is considered. The experimental ACFs show a similar tendency in angular dependence to the theoretical ACF for entangled H(2p) pairs. However, there still remains a considerable difference in the variation magnitude between those experimental and theoretical ACFs. The experimental ACFs show the reverse tendency in angular dependence to the theoretical ACF for H(2p) pairs with definite magnetic quantum number of each hydrogen atom relative to the internuclear axis. We thus conclude that the pair of H(2p) atoms in the photodissociation of H2 is unlikely to be in the definite states of magnetic quantum number of each hydrogen atom relative to the internuclear axis, i.e., unlikely to be in the components of the entangled state of H(2p) pairs. [ABSTRACT FROM AUTHOR]

Double-electron excitations in electron collisions with NH3 are investigated in the range of the outer valence and inner valence excitations by means of angle-resolved electron-photon coincidence measurements. Double-electron and single-electron excitations are termed double and single excitations, respectively, in this article. It is found that the dissociative double excitation resulting in H(2p) formation becomes more dominant over the dissociative single excitation at 100-eV incident energy as the electron scattering angle increases just from 8° to 15°. This remarkable domination is not expected from the independent particle model and strongly supports the double-excitation mechanism through the electron correlation induced by the penetration of the incident electron depth into the valence orbitals of a NH3 molecule. [ABSTRACT FROM AUTHOR]

The absolute values of the cross section for formation of a 2p atom pair in the photoexcitation of H2 and D2 are measured against the incident photon energy in the range of doubly excited states by means of the coincidence detection of two Lyman-α photons. The cross-section curves are explained only by the contribution of the doubly excited Q2 ¹Πu(1) state. The isotope effect on the oscillator strengths of 2p + 2p pair formation for H2 and D2 from the Q2¹Πu(1) state is almost the same as that on the oscillator strengths of 2s + 2p pair formation from the Q2¹Πu(1) state obtained by our group [T. Odagiri et al., Phys. Rev. A 84, 053401 (2011)]. This channel independence indicates that both isotope effects are dominated by the early dynamics of the Q2¹Πu(1) state, before reaching the branching point into 2p + 2p pair formation and 2s + 2p pair formation. [ABSTRACT FROM AUTHOR]