Theoretical characterization of C7, C7-, and C7+

Area of Science:

• Theoretical Chemistry
• Computational Chemistry
• Physical Chemistry

Background:

• Carbon chains exhibit complex isomerism, increasing with chain length.
• Understanding the structures and properties of small carbon clusters like C7 is crucial for various chemical applications.

Purpose of the Study:

• To theoretically investigate the neutral and ionic forms of C7 molecules.
• To identify and characterize stable isomers and electronic states of C7, C7(-), and C7(+).
• To compute key spectroscopic and energetic properties for these carbon species.

Main Methods:

• Density Functional Theory (DFT) using B3LYP/aug-cc-pVTZ for structure searching.
• High-level explicitly correlated coupled-cluster calculations ((R)CCSD(T)-F12) for accurate geometries and spectroscopic data.
• Multi-Reference Configuration Interaction (MRCI) with Complete Active Space Self-Consistent Field (CASSCF) for excitation energies.

Main Results:

• Twelve minimal structures were found for neutral C7, with the linear form being the most stable.
• Fifteen stable forms of C7(-) were characterized, including a doubly degenerate Renner-Teller structure as the global minimum.
• Eleven doublet and three quartet isomers were identified for C7(+), with a cyclic structure as the ground state.
• Accurate rotational constants, harmonic frequencies, electron affinity (3.38 eV), and ionization energy (10.42 eV) were computed for linear C7.

Conclusions:

• The study provides a comprehensive theoretical map of C7, C7(-), and C7(+) isomers and their properties.
• Identified electronic states are suitable for further investigation in reactive processes.
• The computed properties offer valuable data for experimental validation and understanding carbon cluster chemistry.