Electron trapping in strong-field dissociative frustrated ionization of CO molecules

We experimentally investigate the laser-induced dissociative frustrated multiple ionization of CO molecules; in this process one of the released electrons does not escape to the continuum but is eventually trapped into high-lying Rydberg states of the outgoing positively charged nuclear fragments at the ends of the laser pulse, leading to the formation of neutral Rydberg fragments, i.e., C∗ or O∗. By measuring the ejected neutral Rydberg and ionic nuclear fragments as well as the freed electrons in coincidence, we trace the probability of electron trapping by different nuclear fragments and find that formation of C∗ is preferred to O∗. Furthermore, the electron trapping to one of the outgoing nuclear fragments of the breaking molecule can be steered by using a phase-controlled two-color laser pulse. Our results show that Rydberg fragments are more likely to be produced for CO molecules when they are exposed to a laser field pointing from C to O. This orientation-dependent asymmetric emission of the neutral Rydberg fragments is further confirmed in the multiple ionization of CO molecules by using a single-color elliptically polarized femtosecond laser pulse.