High-Energy Molecular-Frame Photoelectron Angular Distributions: A Molecular Bond-Length Ruler

Abstract

We present an experimental and theoretical study of core-level ionization of small hetero-and homo-nuclear molecules employing circularly polarized light and address molecular-frame photoelectron angular distributions in the light's polarization plane (CP-MFPADs). We find that the main forward-scattering peaks of CP-MFPADs are slightly tilted with respect to the molecular axis. We show that this tilt angle can be directly connected to the molecular bond length by a simple, universal formula. The extraction of the bond length becomes more accurate as the photoelectron energy is increased. We apply the derived formula to several examples of CP-MFPADs of C 1s and O 1s photoelectrons of CO, which have been measured experimentally or obtained by means of ab initio modeling. The photoelectron kinetic energies range from 70 to 1000 eV and the extracted bond lengths agree well with the known bond length of the CO molecule in its ground state. In addition, we discuss the influence of the back-scattering contribution that is superimposed over the analyzed forward-scattering peak in case of homo-nuclear diatomic molecules as N2.

Single-photon ionization of aligned H 2+ with near-ionization-threshold photon energy

“…Different from the case of the high-intensity and low-frequency laser field where the mechanism of tunneling ionization dominates, the ionization of atoms or molecules in a low-intensity and high-frequency laser field is dominated by single-photon ionization. For a diatomic molecule or molecular ion with two atomic centers, such as N 2 [24][25][26][27], H 2 [28][29][30][31][32], H + 2 [33,34], O 2 [35], O 2+ 2 [36], Ne 2 [37], CO [38,39], and CO 2+ [40][41][42], during the process of single-photon ionization, the emitting electronic wave with real momentum interferes between these two atomic centers of the molecule. This phenomenon can be understood as the molecular-level double-slit interference.…”