A FOURIER TRANSFORM INFRARED ISOTOPIC STUDY OF THE ν4\nu_{4} STRETCHING MODES OF THE C5C_{5} AND C6C_{6} CLUSTERS IN Ar AT 10 K.1^{1}

$^{1}$Supported by the W.M. Keck Foundation and the Welch Foundation (Grant P-0786). $^{2}$M. Vala. T.M. Chandrasekhar. J. Szezepanski, R. Van Zee, and W. Weltner, JR. J. Chem. Phys. 90, 595 (1989). $^{3}$L.N. Shen and W.R.M. Graham. J. Chem. Phys. 91, 5115 (1989). $^{4}$P. Botschwina and P. Sebald, Chem. Phys. Lett 160, 485 (1989). $^{5}$D.W. Ewing and I. Shavitt, J. Chem. Phys., in press. $^{6}$J,M.L. Martin, J.P. Francois, and R, Gijbels. J. Chem. Phys. 93, 8650 (1990).Author Institution: Department of Physics, Texas Christian UniversityThe $C_{5}$ carbon cluster has been produced by trapping in Ar the products of the VUV-photolysis of 2-methyl-l,3-butadiene or by the high temperature evaporation of graphite. The $\nu_{3}(\sigma_{u}$) stretching mode was earlier observed at $2164.3 cm^{-1}$ and a band at $1544 cm^{-1}$ was attributed to the $\nu_{4}(\sigma_{u}$) vibration of $C_{5}$, but was later assigned to the $\nu_{3}(\sigma_{u}$ vibration of $C_{4}^{3}$. In the present work, the second $C=C$ stretching mode, $\nu_{4}(\sigma_{u}$ of $C_{5}$, has been found at $1446.6 cm^{-1}$. Measurements have been made for all twenty $^{13}C$-substituted isotopomers of linear $C_{5}$. Both the $\nu_{4}$ fundamental frequency and the isotopic shifts are in agreement with recent ab initio calculations done al the coupled electron pair approximation and MP2/DZP $levels.^{4,5}$ Also produced in the high temperature evaporation of graphite was the $C_{6}$ carbon cluster. The present work reports the continuation of the assignment of the $1197.3 cm^{-1}$ band, through extensive $^{13}C$ substitution, to the $\nu_{4}$ stretching mode of $C_{6}$, The results of both the original assignment and the isotopic measurements agree well with recent ab initio calculations done at the $MP2/6-31G^{*}$ $level.^{6}

FIRST DETECTION OF THE ν7(σu)\nu_{7}(\sigma_{u}) STRETCHING FUNDAMENTAL OF LINEAR C9C_{9} AND STUDY OF THE ν5(σu)\nu_{5}(\sigma_{u}) MODE OF LINEAR C7C_{7} IN Ar AT 10 K

1. J.R. Heath and R.J. Saykally, J. Chem, Phys, 93, 8392 (1990).Author Institution: Texas Christian University, Fort Worth, TX 76133.Recent ab initio calculations for the linear $C_{9}$ carbon cluster have shown a notable lack of convergence in the values of the frequencies and intensities predicted for the antisymmetric stretching modes $\nu_{5}, \nu_{6}$, and $\nu_{7}$. This situation has motivated a search for a second antisymmetric fundamental in addition to the $\nu_{5}(\sigma_{u})$ already observed at $2014.28 cm^{-1}$ in the gas $phase.^{1}$ This paper reports Fourier transform infrared observations of $C_{9}$ in solid Ar resulting in the identification for the first time of the $\nu_{7}(\sigma_{u})$ mode at $1601.0 cm^{-1}$. Comparison of $^{13}C$ isotopic shifts measured for over 200 isotopomers with the predictions of DFT (density functional theory) and CCSD (coupled cluster) calculations, conclusively confirms the assignment of the new mode. The results of isotopic measurements for the $\nu_{5}(\sigma_{u})$ antisymmetric stretching mode of linear $C_{7}$ at $1894.3 cm^{-1}$ and comparison with ab initio calculations are also reported

Potential energy surfaces of WC6 clusters in different spin states

Stochastic explorations of the structural possibilities of neutral WC6 clusters in several spin states lead to very rich and complex potential energy surfaces, with geometries quite different from those of pure carbon clusters at the PBE0/def2-TZVP level. The global minimum is predicted to be a triplet-state semicyclic C6 conformation having every carbon in direct coordination to the W atom. Interaction energies are comparable to those of C7 clusters, revealing very strong W–C bonding. Our results suggest that C–C interactions in the clusters should be considered as intermediate between single and double bonds