The 1(5)Π(g) state of C2

Area of Science:

• Theoretical Chemistry
• Molecular Spectroscopy
• Computational Quantum Chemistry

Background:

• The electronic structure of the C(2) molecule is complex and has been a subject of extensive research.
• Accurate spectroscopic characterization of excited states is crucial for understanding molecular behavior and chemical reactions.

Purpose of the Study:

• To compute ab initio spectroscopic constants for the recently identified 1(5)Π(g) state of C(2).
• To validate theoretical methods by comparing calculations with experimental data for known states.

Main Methods:

• Multi-reference configuration interaction (MRCI) level of theory with Davidson's correction.
• Aug-cc-pV6Z basis sets for valence electrons.
• Core-valence correlation and relativistic corrections using quadruple-zeta bases.

Main Results:

• Calculated spectroscopic constants for the 1(5)Π(g) state of C(2).
• Excellent agreement between calculated and experimental spectroscopic data for other C(2) states.
• Predicted vibrational energy (ωe) within a few cm⁻¹ and rotational constants within 0.1% of experimental values.

Conclusions:

• The theoretical treatment accurately reproduces experimental observations for C(2).
• The calculations strongly suggest the observed vibrational level of the 1(5)Π(g) state is v = 0.
• Provides highly accurate theoretical data for the 1(5)Π(g) state of C(2).