Parity alternation of linear ground-state hydrogenated cationic carbon clusters HC_n⁺ (n = 1-10)

Making use of molecular graphics software, we have designed numerous models of HC_n⁺ (n = 1-10) cationic clusters, and performed geometry optimization and vibrational frequency calculation by means of the B3LYP density functional method. The linear ground-state isomers of HC_n⁺ (n = 1-10) are found to be linear with the hydrogen atom located at one end of the carbon chain. When n is odd, the carbon chain is polyacetylene-like in configuration whereas when n is even, the carbon chain displays a polyacetylene-like structure that fades into a cumulenic-like arrangement towards the carbon end. We detected trends of odd/even alternation in electronic configuration, energy difference, ionization potential as well as in certain bond length and certain atomic charge of the linear ground-state HC_n⁺ (n = 1-10) isomers. The results reveal that the odd-n cationic clusters are more stable than the even-n ones; they match the relative yields of HC_n⁺ clusters as revealed in mass spectrometric investigations.