Numerical solutions of the time-dependent Schrödinger equation, using a new unitary numerical method, are used to obtain gauge-independent photoionization angular distributions for two-dimensional (planar) models of aligned ${\mathrm{H}}_2$ and ${{\mathrm{H}}_2}^{+}$ molecules in different electronic states. Simulations are performed with few-cycle attosecond (as) extreme-ultraviolet (xuv) laser pulses at wavelengths $\lambda =$ 10 nm [$\omega =$ 4.56 a.u. (atomic units), $\tau =2\pi /\omega =$ 1.38 a.u. $=$ 33.4 as], and $\lambda =$ 5 nm ($\omega =$ 9.11 a.u., $\tau =$ 16.7 as) for linear and circular polarization ionizations at $R_e=1.675$ a.u., where molecular orbital configurations dominate for which the electron wavelengths ${\lambda }_e⩾R_e$ and at large internuclear distance $R=10$ a.u. (${\lambda }_e<R$) where Heitler-London atomic configurations including ionic states ${\mathrm{H}}^{+}$H${}^{-}$ are more appropriate. The simulations allow one to investigate the effects of electron correlation and entanglement in ${\mathrm{H}}_2$ at different $R$ due to electron spin exchange as compared to the delocalized one-electron ${{\mathrm{H}}_2}^{+}$ system. An ultrashort (delta function) pulse model is used to interpret interferences in momentum distributions.

• Received 30 January 2011

DOI:https://doi.org/10.1103/PhysRevA.83.043418