Precise Access to the Molecular-Frame Complex Recombination Dipole through High-Harmonic Spectroscopy.

Area of Science:

• Quantum Chemistry
• Molecular Spectroscopy
• Atomic, Molecular, and Optical Physics

Background:

• Understanding molecular orbital dynamics is crucial for controlling chemical reactions and developing new materials.
• High harmonic spectroscopy (HHS) is a powerful technique for probing electron dynamics in molecules.

Purpose of the Study:

• To measure the highest-occupied molecular-orbital (HOMO) recombination dipole moment of N₂ in the molecular frame.
• To investigate angle-resolved spectral features associated with autoionizing resonances.
• To enable quantitative comparison with theoretical calculations.

Main Methods:

• Utilized high harmonic spectroscopy (HHS) with a long-wavelength 1.3 μm driving laser.
• Isolated the HOMO in the near-threshold region (19-67 eV).
• Performed precise group delay measurements.

Main Results:

• Reported spectral intensity and group delay measurements of the N₂ HOMO recombination dipole moment.
• Revealed previously unseen angle-resolved spectral features linked to autoionizing resonances.
• Achieved quantitative comparison with advanced correlated 8-channel photoionization dipole moment calculations.

Conclusions:

• The study provides precise experimental data on molecular frame electron dynamics in N₂.
• The findings highlight the importance of autoionizing resonances in HH S.
• The results validate and guide theoretical models for molecular photoionization.