Laser-induced electron recollision inH2and electron correlation

Abstract

Single and double ionization processes are calculated for a 1D model of ${\mathrm{H}}_{2}$ from numerical solution of the time-dependent Schr\"odinger equation in the presence of an intense $I\ensuremath{\leqslant}5\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$, ultrashort $(10\phantom{\rule{0.3em}{0ex}}\text{cycles})$ $800\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ laser pulse. Laser-induced electron recollision, LIERC, is identified from a systematic analysis of bound and continuum populations in the two-electron wave function. Recollision is shown to be responsible for double ionization at lower intensities, $I<{10}^{15}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$ and persists also in the first two excited states of ${\mathrm{H}}_{2}$, the $A\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Sigma}_{u}^{+}$ and $B\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}_{u}^{+}$ states. The effects of the symmetry (antisymmetry) of the two-electrons wave function is found to be dominant at large internuclear distances where enhanced ionization is operative, especially in the $A\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Sigma}_{u}^{+}$, where the exclusion principle suppresses double ionization from LIERC. Furthermore, at large distances, double ionization is shown to occur with equal excitation of the highest occupied and lowest unoccupied molecular orbitals of the ${\mathrm{H}}_{2}^{+}$ core ion. Negligible core excitation occurs at equilibrium.