/en/research/projects/2.3/topics/XUV photoelectron spectroscopy/index.html
2.3 Time-resolved XUV-science
Project coordinator(s): A. Rouzée, S. Patchkovskii
Topic: Time-resolved XUV/X-ray photoelectron imaging and spectroscopy of ultrafast molecular processes

Topic Goals

Following ultrafast molecular dynamics, such as the rotational and vibrational motion, the dissociation and fragmentation dynamics or the internal conversion at conical intersection is one of the main objectives of project 2.3. XUV and X-ray ultrashort laser sources are particularly suitable for probing ultrafast dynamic since the short wavelength combined with its short pulse duration allows to track the positions of individual nuclei within a molecule at the atomic length scale with femtosecond resolution. Different methods to achieve this goal are currently under investigation.

Present key activities

XUV/X-ray photoelectron imaging
Bernd Schütte, Truong Xuan Nguyen, Axel Hundertmark, Arnaud Rouzée

The XUV/X-ray photoelectron imaging method relies on detection of energy- and angle- resolved photoelectron from molecules aligned in the laboratory frame. When an electron is released from an aligned molecule by XUV photoionization, it can directly scatter off other nuclei on their way out leading to features in the photoelectron angular distribution that contain information about positions of individual nuclei. The method is in active development with several key techniques demonstrating significant progress.

High resolution photoelectron/photoions spectroscopy
Christian Neidel, Jesse Klei, Chung-Hsin Yang, Martin Eckstein,
Nickolai Zhavoronkov, Oleg Kornilov

These experiments aim at investigating ultrafast electronic dynamics in gas phase molecules using time-resolved photoelectron and photoion spectroscopy using one photon vis/VUV pump, one photon XUV probe configuration. The XUV pulses with photon energies up to 100 eV is selected by a time-compensated monochromator from an HHG source. The monochromator allows to get sub-10fs, 300 meV bandwidth limited single harmonic source. Studies of ultrafast internal conversion and isomerization with photoelectron and photoion spectroscopy should help to follow molecular dynamics down to the ground state with unprecedented resolution.

Photochemistry at avoided crossings
Hans-Hermann Ritze, Franziska Buchner, Arnaud Rouzée, Andrea Lübcke

We use the velocity map imaging technique to study in detail the wavepacket dynamics of simple molecules like NaI or NO resulting from the excitation with a visible or VUV laser pulse. A special attention is devoted to the study of the wavepacket dynamics at avoiding crossing, which have been notoriously difficult to study in the past. Information about electronic and nuclear coupling at avoiding crossing is obtained experimentally by recording the angle- and kinetic-energy resolved photoelectron spectra after single photon ionization using a second laser excitation.

Other subjects of interest

CRASY: Correlated Rotational Alignment Spectroscopy
Christian Schröter, Thomas Schultz

With correlated rotational alignment spectroscopy (CRASY), we developed an all-optical, multi-pulse experiment that allows the correlated measurement of rotational and mass or photoelectron spectra. The power of this method was demonstrated with the determination of ground-state rotational constants and fragmentation channels for 10 different isotopes in a natural carbon disulfide sample. Future experiments will concomitantly determine rotational spectra, electronic structure, and photochemical dynamics for low-abundance compounds in impure samples or for inseparable molecular isomers, and investigate structure and fragmentation pathways of biomolecular clusters such as DNA base pairs.