Sub-picosecond photodynamics of small neutral copper oxide clusters

Area of Science:

• Physical Chemistry
• Materials Science
• Quantum Chemistry

Background:

• Copper oxide clusters exhibit complex electronic and structural properties.
• Understanding ultrafast dynamics is crucial for materials science applications.
• Previous ionization techniques limited the study of unstable clusters.

Purpose of the Study:

• To investigate the ultrafast dynamics of neutral copper oxide clusters (n < 5) in the gas phase.
• To correlate electronic structure changes with oxidation state using computational methods.
• To demonstrate strong field ionization as a soft ionization technique for unstable clusters.

Main Methods:

• Femtosecond pump-probe spectroscopy was employed to study transient absorption spectra.
• Density functional theory (DFT) calculations determined ground state structures and spin states.
• Time-dependent density functional theory (TD-DFT) calculated topological descriptors for excited states.

Main Results:

• Copper oxide clusters (n < 5) exhibit ultrafast relaxation (100s of fs) and long-lived (>50 ps) responses.
• Increasing oxidation leads to changes in electronic structure, with superoxide formation (O2) observed when oxygen exceeds copper.
• Strong field ionization enabled the study of clusters unstable to nanosecond multiphoton ionization, with laser synergy indicating relative stability.

Conclusions:

• Ultrafast dynamics are strongly linked to the electronic structure and oxidation state of copper oxide clusters.
• Strong field ionization is a viable soft ionization method for studying transient signals of potentially unstable molecular clusters.
• Cluster stability is influenced by the ratio of copper to oxygen atoms, affecting spin states and fragmentation patterns.