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

Abstract

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 C4 n +2 and to a lesser extent the C4 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 C4 n and C4 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).

Ionization potentials, dissociation energies and statistical fragmentation of neutral and positively charged small carbon clusters

“…Our results agree reasonably well with the experimental measurements and those reported in ref. [40]. Second IP decreases with cluster size showing a stabilization for n = 8 − 10.…”

“…As a general trend, first IP slowly decreases with cluster size, but this decrease is not monotonic and present some oscillations. The first ionization potencial has been measured by different authors [31][32][33][34][35][36][37][38][39] and theoretically calculated by Giuffreda et al [40]. We have also included in Fig.…”

A comparative MRD-CI study of the electronic spectrum of linear and cyclic C8+ clusters

“…Therefore excited states and electronic absorption spectra of such charged molecules like C þ 8 are presently of great interest. C þ 8 is known to possess two isomers of comparable energy: a D 1h symmetric linear chain structure (X 2 P g state) and a planar monocyclic ring structure with C 4h symmetry [10,11]. The purpose of the present work is to demonstrate that the electronic spectra can be used to discriminate between the two isomers of C þ 8 in vacuum.…”

“…Two excellent reviews, one by Weltner and van Zee [1] and more recently a second one by Van Orden and Saykally [2] summarise what is known about small carbon clusters. While neutral carbon clusters have been the subject of numerous theoretical studies [2][3][4][5][6][7] and experimental work [1,2,8], much less is known about positively charged species [1,2,[8][9][10][11][12].…”

Theoretical study of the stability of small triply charged carbon clusters Cn3+ (n=3–12)

“…Positively charged carbon clusters have been much less studied theoretically. Giuffreda et al [30] have used density functional theory (DFT) and coupled cluster (CC) methods to evaluate structural, rotational, vibrational, and electronic properties of linear and cyclic singly charged C n + clusters with n = 4-19. For small doubly charged carbon * Corresponding author.…”