Coulomb exploded directional double ionization of N2O molecules in multicycle femtosecond laser pulses

We experimentally investigate Coulomb exploded directional double ionization of N2O molecules in elliptically polarized femtosecond laser pulses.The denitrogenation and deoxygenation channels are accessed via various pathways.It leads to distinct asymmetries in directional breaking of the doubly ionized N2O molecules versus the instantaneous laser field vector, which is revealed by tracing the sum-momentum spectra of the ionic fragments as a recoil of the ejected electrons.Our results demonstrate that the accessibility of the Coulomb exploded double ionization channels of N2O molecules are ruled by the detailed potential energy curves, and the directional emission of the fragments are governed by the joint effects of the electron localization-assisted enhanced ionization of the stretched molecules and the profiles of the molecular orbitals.

Tunnelling of electrons via the neighboring atom

As compared to the intuitive process that the electron emits straight to the continuum from its parent ion,there is an alternative route that the electron may transfer to and be trapped by a neighboring ionic core before the eventual release.Here,we demonstrate that electron tunnelling via the neighboring atomic core is a pronounced process in light-induced tunnelling ionization of molecules by absorbing multiple near-infrared photons.We devised a siteresolved tunnelling experiment using an Ar-Kr+ion as a prototype system to track the electron tunnelling dynamics from the Ar atom towards the neighboring Kr+by monitoring its transverse momentum distribution,which is temporally captured into the resonant excited states of the Ar-Kr+before its eventual releasing.The influence of the Coulomb potential of neighboring ionic cores promises new insights into the understanding and controlling of tunnelling dynamics in complex molecules or environment.

Low-Energy Protons in Strong-Field Dissociation of H_(2)^(+) via Dipole-Transitions at Large Bond Lengths

More than ten years ago,the observation of the low-energy structure in the photoelectron energy spectrum,regarded as an“ionization surprise,”has overthrown our understanding of strong-field physics.However,the similar low-energy nuclear fragment generation from dissociating molecules upon the photon energy absorption,one of the well-observed phenomena in light-molecule interaction,still lacks an unambiguous mechanism and remains mysterious.Here,we introduce a time-energy-resolved manner using a multicycle near-infrared femtosecond laser pulse to identify the physical origin of the light-induced ultrafast dynamics of molecules.By simultaneously measuring the bond-stretching times and photon numbers involved in the dissociation of H_(2)^(+) driven by a polarization-skewed laser pulse,we reveal that the low-energy protons(below 0.7 eV)are produced via dipole-transitions at large bond lengths.The observed low-energy protons originate from strong-field dissociation of high vibrational states rather than the low ones of H_(2)^(+) cation,which is distinct from the well-accepted bond-softening picture.Further numerical simulation of the time-dependent Schrödinger equation unveils that the electronic states are periodically distorted by the strong laser field,and the energy gap between the field-dressed transient electronic states may favor the one-or three-photon transitions at the internuclear distance larger than 5 a.u.The time-dependent scenario and our time-energy-resolved approach presented here can be extended to other molecules to understand the complex ultrafast dynamics.