The ionization energy of C2

Area of Science:

• Molecular Spectroscopy
• Quantum Chemistry
• Atomic and Molecular Physics

Background:

• Accurate ionization energies are crucial for understanding molecular electronic structures and chemical reactions.
• Previous determinations of the C2 molecule's ionization energy lacked the required precision for detailed theoretical comparisons.

Purpose of the Study:

• To determine the ionization energy of the C2 molecule with unprecedented precision (5 meV).
• To investigate the electronic states of C2, specifically the a(3)Πu and X(1)Σg(+) states.
• To validate experimental findings with theoretical quantum thermochemical calculations.

Main Methods:

• Employed resonant two-photon threshold ionization spectroscopy.
• Explored the ionization threshold by pumping the 0-3 band of the 4(3)Πg ← a(3)Πu band system of C2.
• Accounted for spin-orbit and rotational effects in the analysis.

Main Results:

• Determined the ionization energy of the lowest rovibronic level of the a(3)Πu state of C2 to be 11.791(5) eV.
• Calculated the ionization energy of the forbidden origin of the a(3)Πu state to be 11.790(5) eV.
• Experimentally derived ionization energy for the X(1)Σg(+) state C2 is 11.866(5) eV, showing excellent agreement with theoretical calculations.

Conclusions:

• Achieved a 5 meV precision for the C2 ionization energy, an improvement of two orders of magnitude.
• The experimental results strongly support theoretical quantum thermochemical calculations for C2.
• Provides highly accurate data for fundamental molecular physics and astrochemistry applications.