Intramolecular electron diffraction in vibrationally resolvedK-shell photoionization of methane

Abstract

Current techniques based on x-ray or electron diffraction are successfully employed for structure determination in condensed matter but are sometimes limited when applied to low density media such as the gas phase. Here we show that vibrationally resolved photoelectron spectroscopy based on x rays generated by third generation synchrotron light sources can be used to infer the structure of isolated molecules in a simple and efficient way. In particular, we show that vibrational ratios obtained from inner shell C 1s photoelectron spectroscopy of isolated methane molecules exhibit pronounced oscillations that are the fingerprints of electron diffraction by the surrounding atomic centers, thus providing the necessary information for the determination of the molecular geometry.

Intramolecular photoelectron diffraction in the gas phase

“…25 There is recent evidence that electrons ejected from a very localized region of a molecule, such as the 1s orbital of first-row atoms, also lead to oscillating patterns in the v-ratios as a result of electron scattering by the peripheral atomic centers of the molecule. 26 In this paper, we unambiguously show that the v-ratios for photoionization of CF 4 , BF 3 , and CH 4 from the 1s orbital of the central atom strongly oscillate as functions of photoelectron energy. The very good agreement between first-principles static-exchange and time-dependent density functional theory calculations and high resolution measurements, as well as the qualitative agreement at high energies with a simple model show that the origin of these oscillations is the diffraction by the surrounding H and F atoms.…”

Vibrational branching ratios in the photoelectron spectra of N2 and CO: interference and diffraction effects

“…In their most sophisticated version, they can even include interchannel couplings and describe some autoionization processes. They have even been used to evaluate vibrationally resolved cross section in polyatomic molecules 124,125 . In this section, we will describe the extension of these DFT-like methods to include the nuclear motion in the Born-Oppenheimer approximation.…”

“…It must be stressed however that, although interchannel coupling and singly excited autoionizations are included, double or higher electron excitations are presently outside the scope of the approach. In many cases, the local density approximation is appropriate to treat photoabsorption processes in "small" systems (in atoms 144 as well as in molecules 78,107,124,125,143,[146][147][148] ).…”

Probing and extracting the structure of vibratingSF6molecules with inner-shell photoelectrons

“…Since x-ray diffraction suffers from weak elastic scattering cross sections, to take advantage of the currently available and future short extreme ultraviolet (XUV) or x-ray pulses, different schemes have been proposed for gas-phase molecules which rely on photoelectron diffraction [21][22][23][24][25][26][27][28][29]. In contrast to the TRPES method that probes valence electrons, photoelectron diffraction with localized inner-shell electrons is capable of directly imaging atomic positions.…”