Structure, Dissociation Energies, and Harmonic Frequencies of Small Doubly Charged Carbon Clusters C_n²⁺ (n = 3−9)

Abstract

We have studied the structure of small doubly charged carbon clusters using density functional (DFT) and coupled-cluster (CC) theories. We have found that, with the exception of C4 2+ and C7 2+, the most stable geometry corresponds to linear structures of D ∞ h symmetry. This is at variance with the behavior observed in neutral and singly charged carbon clusters. We have also evaluated dissociation energies corresponding to various dissociation channels that are useful in mass spectrometry experiments. This requires that absolute energies of neutral and singly charged species are evaluated at the same level of theory. As a byproduct of the latter calculations, we have evaluated first and second ionization potentials that are still unavailable in the literature. Harmonic frequencies for the doubly charged species have been also evaluated.

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

“…These results are in agreement with calculations of the potential energy surface evaluated with multireference methods (MR-DCI) [41,42]. The smallest doubly charged cluster that is stable against Coulomb explosion is C 2+ 5 [28,43]. The lowest dissociation energy of this molecule corresponds to channel C + 4 /C + .…”

“…The B3LYP functional has been proved to be a good choice for the description of carbon clusters [25]. In the case of small carbon clusters, the calculated geometries and the vibrational frequencies are very close to those obtained at higher levels of calculations [26][27][28]. More accurate values of electronic and binding energies have been obtained with the coupled cluster theory CCSD(T)/6-311+G(3df), which includes all single and double excitations, as well as triple excitations in a perturbative way [29], and made use of the B3LYP optimized geometry.…”

“…We have evaluated several properties of carbon clusters with linear and cyclic geometries and with different spin multiplicities (singlet and triplet for the neutral and doubly charged species and doublet and quadruplet for the singly charged ones) [28]. To introduce all the isomers in the MMMC simulations has been shown to be crucial to correctly describe the fragmentation process [19,22] the most stable isomer for each cluster size and charge, i.e., they are adiabatic energies.…”

Ionization Thresholds of Small Carbon Clusters: Tunable VUV Experiments and Theory

“…79-80 Table 3 contains predicted adiabatic IPs from the present work and those of Guiffreda et al 55a and Díaz-Tendero et al 56 Comparing optimized geometries of Guiffreda et al, 55a we were unable to reproduce their reported IPs for these three systems. The source of this discrepancy is therefore unclear.…”

“…Extensive computational studies have examined these neutral clusters [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] and their corresponding ions. [50][51][52][53][54][55][56][57][58][59][60][61] Spectroscopy has been applied to the neutral systems in the gas phase 1,5,[62][63][64] and in matrix isolation experiments. 1,5,[65][66][67][68][69][70] More recent experiments have employed mass-selection prior to matrix spectroscopy.…”