III. Formation of Carbon Clusters 2317 IV. Thermodynamic Properties 2319 V. C2 2319 A. Structure and Spectroscopy 2319 B. C2 2320 C. C2 2321 VI. C3 2321 A. Early Experimental Work 2321 B. Mid-IR and Far-IR Spectroscopy 2321 C. Electronic Spectroscopy 2323 1. The Σu + Ground State 2323 2. The AΠu State 2324 3. The Σu + State 2324 4. The aΠu and bΠg States 2325 5. Other Band Systems 2326 D. C3 in the Interstellar Medium 2326 E. C3 2326 F. C3 2327 VII. C4 2327 A. Theory 2327 B. Experiment 2328 1. The Rhombic Isomer 2328 2. The Linear Isomer 2328 C. Excited Electronic States 2330 D. C4 2331 E. C4 2332 VIII. C5 2332 A. Theory 2332 B. Experiment 2332 C. Excited Electronic States 2334 D. C5 2334 E. C5 2335 IX. C6 2335 A. Theory 2335 B. Experiment 2336 1. The Cyclic Isomer 2336 2. The Linear Isomer 2336 C. Excited Electronic States 2337 D. C6 2338 E. C6 2338 X. C7 2338 A. Theory 2338 B. Experiment 2338 C. Excited Electronic States 2340 D. C7 2340 E. C7 2340 XI. C8 2341 A. Theory 2341 B. Experiment 2342 1. The Cyclic Isomer 2342 2. The Linear Isomer 2342 C. Excited Electronic States 2342 D. C8 2342 E. C8 2342 XII. C9 2343 A. Theory 2343 B. Experiment 2343 C. Excited Electronic States 2345 D. C9 2345 E. C9 2345 XIII. C1

http://www.cchem.berkeley.edu/rjsgrp/publications/papers/1998/200_orden_1998.pdf

Small carbon clusters: spectroscopy, structure, and energetics.

Over the past two decades, the identification and characterisation of interstellar molecules has often benefitted from a fruitful interplay between theoretical chemistry, laboratory spectroscopy and (radio) astronomy. The article reports on various examples of this sort, concentrating on carbon chains which represent the most prominent structural motif among currently known interstellar molecules. Results of large-scale coupled cluster calculations are reported for cyanopolyynes (HC2n+1N) up to n = 5, the corresponding radicals C2n+1N, linear silicon carbides (SiCn), carbon–sulfur and pure carbon chains. Throughout, detailed comparison with experimental data is made wherever possible.

Spectroscopic properties of interstellar molecules: Theory and experiment

The structure and energetics of the ring isomers of C(4n+2) (n=3-5) carbon clusters were studied by using coupled-cluster singles and doubles excitation theory to overcome the vast differences existing in the literature The results obtained in the present study clearly indicate that C(14), C(18), and C(22) carbon rings have bond-length and bond-angle alternated acetylenic minimum energy structures Contrarily, density functional theory calculations were unable to predict these acetylenic-type structures and they ended up with the cumulenic structures It is found from the coupled-cluster studies that the lowest-energy ring isomer for the first two members of C(4n+2) series is a bond-angle alternated cumulenic D((2n+1)h) symmetry structure while the same for the remaining members is a bond-length and bond-angle alternated C((2n+1)h) symmetry structure In C(4n+2) carbon rings, Peierls-type distortion, transformation from bond-angle alternated to bond-length alternated minimum energy structures, occurs at C(14) carbon ring

/pdf/ccsd-calculations-on-c14-c18-and-c22-carbon-clusters-156av5frw2.pdf

CCSD calculations on C14, C18, and C22 carbon clusters

The surface plasmon polariton-enhanced Raman spectra of size-selected C16, C18, and C20 clusters isolated in nitrogen matrices are presented along with the calculated vibrational frequencies for the ring and linear chain isomers. The Raman spectra, recorded at a range of excitation wavelengths from 457.9 to 670 nm, show strong resonance enhancement for the three clusters. The calculated vibrational frequencies for ring and linear chain isomers and the cage and bowl structures for C20 are compared to the experimental frequencies. Systematic shifts in the series of peaks in the 200 cm−1 region for C16, C18, and C20 suggest that the observed isomers have the same geometry, thereby ruling out the bowl and cage isomers for C20. The measured spectra appear to be most consistent with the linear chain isomer. This high-energy isomer may be produced during neutralization of the deposited cluster ions.

/pdf/raman-spectra-and-calculated-vibrational-frequencies-of-size-48kjmna8s2.pdf

Raman spectra and calculated vibrational frequencies of size-selected C16, C18, and C20 clusters

Rhomboidal SiC 3

The cyclic C6 cluster has been identified for the first time in Fourier transform infrared spectra of the products from the laser evaporation of graphite rods trapped in Ar at ∼10 K. Measurements on spectra produced using both 12C- and 13C-enriched rods combined with the results of new density functional theory calculations performed in the present work as well as previous calculations by Martin and Taylor, have resulted in the assignment of the most intense infrared active mode, ν4(e′)=1694.9 cm−1 of the cyclic C6 isomer with D3h symmetry. This assignment is based on excellent agreement of the frequency, 13C isotopic shifts, and relative intensities with the theoretical predictions.

Detection of cyclic carbon clusters. II. Isotopic study of the ν12(eu) mode of cyclic C8 in solid Ar

Fourier Transform Infrared Observation of SiCn Chains. II. The ν1(σ) Mode of Linear SiC7 in Ar at 10 K

The linear SiC9 cluster has been detected for the first time in Fourier-transform infrared spectra observed when the products from the laser evaporation of Si/C rods were trapped in Ar at ∼10 K. Comparison of 13C isotopic shift measurements with the results of density functional theory calculations (DFT) confirms the identification of the ν4(σ) mode of SiC9 at 1935.8 cm−1.

Fourier-transform infrared observation of SiCn chains. I. The ν4(σ) mode of linear SiC9 in Ar at 10 K

A Fourier transform infrared investigation of the 13C isotopic spectrum of linear C12 in solid Ar coupled with density functional theory calculations at the B3LYP/cc-pVDZ level has resulted in the identification of the ν8=1997.2 and ν9=1818.0 cm−1 stretching modes. Agreement between experimental measurements and theory is very good. The identification of a third mode ν7=2140.6 cm−1 is considered tentative.

Fourier transform infrared isotopic study of the C12 chain trapped in solid Ar

A recent proposal to assign or reassign absorptions in Fourier transform infrared spectra of the products of evaporating graphite trapped in argon matrices to linear C13 and cyclic C8 has been examined. An analysis of the experimental and theoretical data presented indicates that the claimed identification of linear C13 is unwarranted. Simulations of spectra based on density functional theory calculations and isotopic shift data indicate that an absorption at 1818.0 cm−1 belongs to a carbon chain, and do not support a revision of our earlier identification of the ν12(eu) fundamental of cyclic C8 at 1844.2 cm−1.

Shunlin Wang

Papers

Detection of cyclic carbon clusters. II. Isotopic study of the ν12(eu) mode of cyclic C8 in solid Ar

Fourier Transform Infrared Observation of SiCn Chains. II. The ν1(σ) Mode of Linear SiC7 in Ar at 10 K

Fourier-transform infrared observation of SiCn chains. I. The ν4(σ) mode of linear SiC9 in Ar at 10 K

Fourier transform infrared isotopic study of the C12 chain trapped in solid Ar

On the identification of the vibrational spectrum of cyclic C8 in solid Ar