Structural, Rotational, Vibrational, and Electronic Properties of Ionized Carbon Clusters Cn+ (n = 4−19)

The structures, rotational moments, vibrational normal modes, and infrared spectra of small to medium-size ionized carbon clusters C n + ( n = 4−19) are investigated using density functional (DFT) and coupled cluster (CC) theories. Comparison is made with the neutral systems from which they derive. In contrast to previous restricted open-shell Hartree−Fock (ROHF) results by von Helden and co-workers, electron correlation is shown to strongly limit distortions of the structure upon an adiabatic ionization process. Nonetheless, for such a process, the C 4 n +2 and to a lesser extent the C 4 n +1 cyclic systems are found to evolve from an essentially regular (i.e., cumulenic) pattern to a more alternating (i.e., polyynic) structure in their ionized forms, whereas the opposite trend is observed for the C 4 n and C 4 n +3 rings. Similarly, linear carbon clusters, which can be regarded as mostly cumulenic in their neutral form, tend to become more polyynic after ionization. Rotational moments, IR spectra, and adiabatic ionization potentials as well should provide specific markers of these contrasted characters and behaviors. It has been found that the linear cations show a much more pronounced IR intensity than the cyclic ones. Many of the studied species show a strong absorption in certain regions of the spectrum (e.g., around 2036 cm -1 ).