Attosecond photoionization of coherently coupled electronic states

We study analytically the photoionization of a coherent superposition of atomic and molecular electronic states by an ultrashort, attosecond x-ray pulse. We show that the broad photoelectron spectrum contains detailed information about the time-dependent electron wave packet. The asymmetry of the photoelectron momentum distribution measures the momentum asymmetry of the initial bound-state wave packet. We show that molecular interference modulates the time-dependent photoelectron spectrum and asymmetry. The modulation also depends on the internuclear separation. The photoelectron spectrum and its asymmetry monitors coherent electron motion and in principle electron transfer on the attosecond time scale.