Isomers and excitation energies of C4

Abstract

Coupled-cluster (CC) and many-body perturbation theory (MBPT) studies of the rhombic and linear structures of C4 are reported. For each isomer, the electronic spectra is obtained, and comparisons are made with experimental matrix-isolated ESR and electronic spectra. The closed-shell 1Ag rhombic ground state is found to be more stable than the 3∑−g state of the linear isomer by 5 kcal/mol at the highest level of calculation performed (CCSDT-1). However, the predicted spectrum for linear C4 is in reasonable agreement with the observed results. An allowed electronic transition for the rhombus is predicted to lie in the same region, suggesting the possibility that both isomers could coexist in the experiment. Finally, vibrational frequencies for the rhombic isomer are calculated using analytical second-order MBPT second derivatives to aid in the experimental identification of this transient species.

Synthesis of C60 from Small Carbon Clusters

“…The temperature dependence of Κ is plotted in Figure 6 for both C. and C 1Q . For the C 4 cluster, the rhombic and linear structures are calculated to be almost isoenergetic, and the rhombic structure is slightly favored (by ~0-5 kcal/mol) (22)(23)(24). Figure 6 shows that the high-temperature form is clearly the linear one, as expected.…”

“…The even-numbered members of this series are calculated to exist as radicals, with 3 Σ ground states, and *Σ ground states are predicted for the odd-numbered chains. In addition, lowlying cyclic structures for the C 4 , C^, and C g clusters are also predicted (22)(23)(24)(25). Much of this theory for the linear structures has been confirmed by high-resolution infrared spectroscopy (13)(14)(15)(26)(27)(28)(29)(30)(31)(32)(33), and experimental data that have been applied to the determination of the structures of triplet linear C 4 and singlet linear C 9 are presented in Figures 4 and 5, respectively.…”

“…Structures and vibrational frequencies from experiment (26) (where available) and ab initio theory (22)(23)(24)36) were used as input. The temperature dependence of Κ is plotted in Figure 6 for both C. and C 1Q .…”

Infrared laser spectroscopy of jet-cooled carbon clusters

“…Recent experiments [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] as well as high level ab initio calculations [19][20][21][22][23][24][25][26][27][28][29][30] have largely vindicated the description originally put forth by Pitzer and Clementi [31] in 1959. Clusters with odd numbers of carbons possess linear singlet ground states, whereas even numbered clusters have two low-lying isomers, a triplet linear form and a singlet cyclic form.…”

A critical comparison of MINDO/3, MNDO, AM1, and PM3 for a model problem: Carbon clusters C2‐C10. An ad hoc reparametrization of MNDO well suited for the accurate prediction of their spectroscopic constants

“…For C3, a n almost perfect agreement with the experimental value is obtained. For the linear form of C4, the large difference between outer (1.314 A) and inner (1.270 A) bond is not a n artifact of the computational method (as argued in another context in Bernholc and P h i l l i p~~~) : large differences were also predicted at the SCF (1.308 and 1.283 A) a n d MP4D (1.330 a n d 1.305 A) levels by Magers et al 28 behaves somewhat like that of cyclic Cs. The CIO system clearly deserves further study.…”