Probing the interplay between geometric and electronic-structure features via high-harmonic spectroscopy.

Area of Science:

• Quantum Chemistry
• Molecular Spectroscopy
• Attosecond Science

Background:

• The recombination dipole matrix element (RDME) governs electron recombination dynamics.
• Understanding molecular structure influences electron behavior during recombination.
• High-harmonic spectroscopy is a powerful tool for probing ultrafast molecular processes.

Purpose of the Study:

• To measure molecular-frame RDMEs in CO2, N2O, and OCS.
• To investigate the role of molecular geometry and electronic structure in RDME.
• To identify interference phenomena affecting RDME in these molecules.

Main Methods:

• High-harmonic spectroscopy was employed for molecular-frame measurements.
• Measurements were conducted on aligned and unaligned molecular samples.
• Ab initio calculations using time-dependent density functional theory were performed for comparison.

Main Results:

• RDMEs in CO2, N2O, and OCS show two-center interference minima dependent on molecular alignment.
• OCS exhibits anomalous phase shifts in its two-center minimum, differing from CO2 and N2O.
• A Cooper-like electronic structure minimum, in addition to the geometric minimum, is proposed for OCS.

Conclusions:

• The RDME in OCS is influenced by both geometric and electronic structure interferences.
• An empirical model was developed to describe these combined interference effects.
• Destructive interference in unaligned samples can reduce yields at high photon energies.