A theoretical study on structure and spectroscopy of C4H2+ isomers

- Linear chain cation HCCCCH+ is the lowest energy species of this stoichiometry.
- Cyclic C4H2+ isomers are more likely to occur than respective neutral molecules.
- Among C4H2+ isomers, HCCCCH+ has outstandingly strong visible bands.
- Predictions on microwave and IR spectroscopy of C4H2+ isomers are given.