Resolving s-trans-dominant ionization dynamics in tiglic aldehyde using VUV-MATI spectroscopy and PES analysis.

Area of Science:

• Physical Chemistry
• Molecular Spectroscopy
• Quantum Chemistry

Background:

• Conjugated carbonyl compounds exhibit complex electronic and conformational behaviors.
• Understanding conformer-specific ionization is crucial for characterizing molecular dynamics.
• Tiglic aldehyde (TA) serves as a model system for α,β-unsaturated aldehydes.

Purpose of the Study:

• To investigate the conformational preferences and ionization dynamics of Tiglic aldehyde (TA).
• To elucidate the electronic and structural changes occurring during TA ionization.
• To establish a framework for studying conformer-specific ionization in related molecules.

Main Methods:

• High-resolution vacuum-ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy.
• Infrared double-resonance techniques.
• Computational methods including Franck-Condon simulations and 2D potential energy surface (2D-PES) mapping.

Main Results:

• Under jet-cooled conditions, TA exists almost exclusively as the s-trans conformer with an adiabatic ionization energy of 77,183 ± 4 cm⁻¹.
• The s-trans conformer, dominant in the neutral state, becomes less stable than the s-cis form upon ionization due to electron removal from the carbonyl π orbital.
• Ionization strongly activates the formyl torsional mode, leading to observed vibrational progressions and potential dephasing at higher energies.

Conclusions:

• The study provides the first conformer-resolved view of Tiglic aldehyde's ionization behavior.
• Conformational reordering upon ionization is driven by shallow torsional potentials and electronic effects.
• Accurate theoretical descriptions require advanced correlated ab initio and DFT methods.