Fourier transform infrared isotopic studies on novel metal-carbon clusters trapped in Ar matrix environments

Abstract

The characterization of the vibrational spectra and structures of small metal-carbon (MnCm) clusters is important to the detection of astrophysical species and may elucidate the bonding and growth mechanisms of metallocarbohedrenes, or metcars. Additionally, transition metal-carbon clusters have applications in modern materials science as catalysts for nanomaterial formation. A new experimental apparatus for the preparation of MnCm clusters has been designed and constructed , incorporating a new closed cycle refrigeration system, a chamber for the deposition of samples, associated vacuum system, and a fully automated mechanism to simultaneously translate and rotate carbon and metal rods during laser ablation. A new technique for fabricating carbon rods has been developed to expedite carbon rod production and to facilitate the formation of the MnCm clusters studied.

Fourier transform infrared (FTIR) investigations have been done for the first time on transition metal-carbon clusters. The molecular clusters were formed by trapping the products from dual laser ablation of metal and carbon rods in solid Ar at ~10 K. Comparing FTIR measurements of vibrational fundamentals and 13C isotopic shifts with the predictions of density functional theory (DFT) calculations has enabled the identification of five novel metal-carbon molecules, establishing their ground state geometries and permitting the assignment of vibrational fundamentals, including the ?1(s) modes of (5?) linear CrC3, (2?) linear CoC3, and (2?) linear CuC3 at 1789.5, 1918.2, and 1830.0 cm-1, respectively, the ?3(su) =1624.0 and ?4(su)=528.3 cm -1 modes of (1Sg+) linear AlC3Al, and the ?2(s) =1210.9 cm-1 mode of linear AlC3.

Evidence for the tentative identification of the ?1(a1)=1554.3 cm-1 mode of (3B1) fanlike CrC4 and the ?4(su)=1987.3 cm-1 mode of (1Sg+) linear AlC4Al is also presented. All FTIR measurements of vibrational frequencies and 13C shifts are in very good agreement with DFT predictions, resulting in the first identification of vibrational fundamentals and the characterization of molecular geometries for these species specifically and for transition metal-carbon clusters in general. A catalog of potential VnCm absorptions has also been developed to aid in future vanadium-carbon studies.