The electronic spectrum of C₅²

Toggle Background

Multi-reference configuration interaction calculations were employed to characterize the electronic states of linear C₅ up to an energy of about 6 eV [8]. The orbital energies of linear C₅ are given as:

The calculations at the linear species did not match the experimental data very well since the X¹$\Sigma_{g}^{+}$$\to$ ¹$\Pi_{u}^{}$ transition was calculated to be at 2.9 eV while the conventional assignment from the experiment was at 2.43 eV. Relaxing the geometry according to C_2v and C_2h geometries

we found that transition moments of the "forbidden" ¹$\Sigma_{u}^{-}$ and ¹$\Delta_{u}^{}$ states at about 2.5 eV increase rather rapidly while the potential stays almost flat as shown below:

Accordingly the measured 2.43 eV should be assigned to these "forbidden" states while the ¹$\Pi_{u}^{}$ state was finally observed at 2.78 eV matching the calculated 2.9 eV reasonably well.

Footnotes

...₅²

In cooperation with J. P. Maier et. al., University of Basel and S. D. Peyerimhoff, University of Bonn