Ultrafast X-ray Diffraction Probe of Coherent Spin-State Dynamics in Molecules

Area of Science:

• Molecular dynamics
• Quantum chemistry
• Spectroscopy

Background:

• Coherent spin-state dynamics are crucial for understanding molecular behavior.
• Observing these dynamics requires advanced techniques with high temporal and spatial resolution.
• Nitric oxide (NO) molecules offer a model system for studying spin-orbit coupling.

Purpose of the Study:

• To introduce a novel approach for probing coherent spin-state dynamics in molecules.
• To demonstrate the capability of ultrafast X-ray diffraction (UXRD) in capturing spin dynamics.
• To image the spatial spin density and retrieve the electronic density matrix of molecules.

Main Methods:

• Utilizing circularly polarized hard X-ray pulses for probing.
• Preparing dynamically aligned nitric oxide (NO) molecules in a coherent superposition spin-orbit coupled electronic state via stimulated Raman scattering.
• Employing ultrafast X-ray diffraction (UXRD) to capture quantum beating and spatial spin density.

Main Results:

• Successfully revealed quantum beating of the coherent spin-state wave packet in NO molecules.
• Demonstrated imaging of the spatial spin density distribution within the molecule.
• Showed the retrieval of the electronic density matrix using circularly polarized UXRD signals.

Conclusions:

• Ultrafast X-ray diffraction (UXRD) is a powerful tool for tracking transient spatial wave functions.
• This method enables the study of molecular dynamics involving the spin degree of freedom.
• The approach opens new avenues for investigating complex molecular behaviors at the ultrafast timescale.