Theoretical study on the structures and properties of hydrogen-doped cationic carbon clusters C_nH₂⁺ (n = 3–10)

Graphical abstract: - Highlights: • The ground-state isomers of the C_nH₂⁺ (n = 3–10) clusters are defined. • The electronic structures of the G-S isomers of C_nH₂⁺ (n = 3–10) are explored. • The C_n chains of the clusters with even-n display quasi-polyacetylene-like structures. • The even-n cationic clusters are more stable than the odd-n ones. • The trend of parity alternation is explained based on a series of properties. - Abstract: Systematic study on the electronic/geometrical structures and the parity alternation effect of hydrogen-doped cationic carbon clusters C_nH₂⁺ (n = 3–10) have been carried out at the density functional theory level. The linear isomers of the clusters have been defined as the ground-state (G-S) isomers. The carbon chain with even-n is quasi-polyacetylene-like in configuration; whereas when n is odd, the carbon chain displays a quasi-polyacetylene-like structure that fades into a cumulenic-like arrangement towards the center of the chain. The even-n cations are more stable than the odd-n ones. Theoretical explanations for the trend of even/odd alternation have provided based on a series of properties of the systems. The findings accord with the relative abundance of C_nH₂⁺ species as recorded in mass spectrometric investigations