Abstract
Author(s): Heck, S; Gatton, A; Larsen, KA; Iskandar, W; Champenois, EG; Strom, R; Landers, A; Reedy, D; Dailey, C; Williams, JB; Severt, T; Jochim, B; Ben-Itzhak, I; Moshammer, R; Dorner, R; Slaughter, DS; Weber, T | Abstract: We present an experimental investigation of symmetry breaking of H2 and D2 molecules after single photoionization due to the Coulomb field of the emitted slow electron interacting with the parent cation during dissociation. The experiments were carried out by measuring the three-dimensional momentum vectors of the photoelectron and recoiling ion in coincidence using a reaction microscope. For photon energies close to threshold, the low-energy photoelectron influences the dissociation process, which results in an asymmetric molecular frame photoelectron angular distribution. This can be explained by the retroaction of the Coulomb field of the photoelectron on its parent ion and has been recently experimentally demonstrated by M. Waitz et al. [Phys. Rev. Lett. 116, 043001 (2016)PRLTAO0031-900710.1103/PhysRevLett.116.043001], confirming theoretical predictions by V. V. Serov and A. S. Kheifets [Phys. Rev. A 89, 031402(R) (2014)PLRAAN1050-294710.1103/PhysRevA.89.031402]. High-momentum resolution and a new series of photon energies just above the dissociation threshold enable the observation of a strong influence of the electron energy and nuclear kinetic energy on the electron localization process for energies below ∼100 meV, which so far has neither been observed nor discussed by theory. Exploring the limitations of the retroaction mechanism at our lowest photon energy, we are able to single out a sensitive testbed and present data of non-Born-Oppenheimer dynamics of the simplest molecular system for future benchmark computational treatments.
Highlights
Symmetry is an important property of atoms and molecules in photoionization processes
We have performed a detailed investigation of symmetry breaking in the molecular frame photoelectron emission pattern for the dissociative photoionization of diatomic molecules H2 and D2
For low photon energies we find that the Coulomb field of the ejected electron couples the electron and nuclear dynamics via retroaction, which is sensitive to the kinetic energies of the particles
Summary
Symmetry is an important property of atoms and molecules in photoionization processes. In the photodissociation of H2 molecules with linearly polarized light, the coherent superposition of gerade and ungerade electronic states, caused by autoionization, leads to an asymmetric photoelectron emission pattern that is highly sensitive to the kinetic energies of the electron and recoiling nuclear fragments. In this paper we focus on a recently discovered fundamental way to coherently mix states of gerade and ungerade parity, using an internal field In this scenario we lower the photon energy toward the threshold of dissociation, creating ever. Slower photoelectrons in a series of measurements For such low-energy photoelectrons, the Coulomb field of the outgoing electron, scaling as 1/r, is strong enough to couple the 1sσg and 2pσu states of the parent ion and break the symmetry in the direction to which the bound electron localizes via retroaction. In this paper we again study the retroaction process in the photodissociation of H2 and D2 molecules, in order to shine more light on its sensitivity to the kinetic energies of the free particles and the coupling of electron and nuclear dynamics during the dissociation, which is of particular relevance when light atoms such as hydrogen are involved [9,10]
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