Quantum Chemical Studies of Carbon Chain Molecules

Quantum chemical investigations of carbon chain molecules have advanced our understanding of their structure, stability and spectral characteristics. These linear and quasi-linear systems encompass polyynes, cumulenes and related carbenes featuring elongated chains of sp-hybridised carbon atoms. High-level ab initio methods such as coupled cluster theory and multi-reference treatments, combined with density functional theory (DFT), enable accurate determination of geometries, energetics and spectroscopic constants. Vibrational perturbation theory provides anharmonic corrections for vibrational frequencies, while rotational constants derived from equilibrium structures inform rotational spectroscopy. These studies support laboratory detection, guide astronomical searches for interstellar species and underpin applications in materials science. Key challenges include accounting for electronic correlation in biradical intermediates and the sensitivity of predicted observables to basis set selection. Progress in composite theoretical protocols and systematic benchmarking of DFT functionals has closed the gap between theory and experiment, facilitating reliable prediction of dipole moments crucial for radioastronomical observation.

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Quantum Chemical Studies of Carbon Chain Molecules publication trend

The graph below shows the total number of articles in quantum chemical studies of carbon chain molecules across all publications each year (not limited to Nature Index journals).

Technical terms

Coupled cluster CCSD(T): An ab initio method including single, double and perturbative triple excitations to capture electron correlation.

Density functional theory (DFT): A computational approach that uses electron density to approximate the many-body electronic energy.

Polyynes: Linear carbon chains with alternating single and triple bonds.

Vibrational perturbation theory (VPT2): A method to include anharmonic effects in vibrational frequency calculations.

Rotational constants: Parameters defining the spacing of rotational energy levels, critical for microwave spectroscopy.

Permanent dipole moment: A measure of charge separation in a molecule that enables detection via rotational transitions.

References

1. CCSD(T) Rotational Constants for Highly Challenging C5H2 Isomers—A Comparison between Theory and Experiment. Molecules (2023).
2. HCnH− Anion Chains with n ≤ 8 Are Nonlinear and Their Permanent Dipole Makes Them Potential Candidates for Astronomical Observation. Molecules (2022).
3. Energetic and Spectroscopic Properties of the Low-Lying Isomers of C5H: A High-Level Ab Initio Study. Atoms (2023).