Photodissociation of Noble Metal-Doped Carbon Clusters

Abstract

Noble metal carbide cluster cations (MC(n)(+), M = Cu, Au) are produced by laser vaporization in a pulsed molecular beam and detected with time-of-flight mass spectrometry. Copper favors the formation of carbides with an odd number of carbon atoms, while gold shows marked drops in ion intensity after clusters with 3, 6, 9, and 12 carbons. These clusters are mass selected and photodissociated at 355 nm. Copper carbides with an odd number of carbons fragment by eliminating the metal from the cluster; for the small species it is eliminated as Cu(+) and for the larger species it is lost as neutral Cu. Copper carbides with an even number of carbons also lose the metal, but in addition to this they eliminate neutral C(3). This even-odd alternation, with the even clusters having mixed fragments, holds true for clusters as large as CuC(30)(+). No loss of C(2) is observed for even the largest clusters studied, indicating that fullerene formation does not occur. The gold carbide photodissociation data closely parallel that of copper, with even clusters losing primarily C(3) and odd ones losing gold. Comparisons to known carbon cluster ionization potentials give some insight into the structures of carbon photofragments. DFT calculations performed on CuC(3-11)(+) allow comparisons of the energetics of isomers likely present in our experiment, and metal-carbon dissociation energies help explain the even-odd alternation in the fragmentation channels. The simplest picture of these metal-doped carbides consistent with all the data is that the small species have linear chain structures with the metal attached at the end, whereas the larger species have cyclic structures with the metal attached externally to a single carbon.

Probing the electronic structure and Au–C chemical bonding in AuC2− and AuC2 using high-resolution photoelectron spectroscopy

“…Apart from mass spectrometric observations of the Au n C m + and Au n C m − species, 11,12 there is no experimental structural or spectroscopic information on any Au-C clusters, except a very recent PES and computational study on AuC 2 − . 13 In this work, Visser et al 13 reported interesting PE imaging on AuC 2 − in the photon energy range from 610 nm to 585 nm, showing a single vibrational progression starting at an electron binding energy of 1.442 eV with a vibrational frequency of 528 cm −1 due to the Au-C stretching in neutral AuC 2 .…”

Laser ablation synthesis of new gold carbides. From gold‐diamond nano‐composite as a precursor to gold‐doped diamonds. Time‐of‐flight mass spectrometric study

“…Recently, we have preliminarily reported that several gold carbides can be obtained via laser ablation synthesis or laser desorption ionization (LDI) using mixtures of nano‐gold with various carbonaceous materials such as fullerene (C 60 ), graphite, and carbon nano‐tubes (CNT) as precursors. Similarly, the formation of gold carbides from various precursors has also been reported …”

HIGHLY UNSATURATED PLATINUM AND PALLADIUM CARBENES PtC3 AND PdC3 ISOLATED AND CHARACTERIZED IN THE GAS PHASE

“…Harding et al identified aPt 3 C + cluster ion [25] for which the geometry is analogous to acarbonate ion and hence consistent with the prediction of the model provided by Pyykkç et al [2] The geometries of other platinum/carbon clusters,which have not yet been observed or characterized, may perhaps be predicted by analogy with other oxocarbons.F or example,m ellitic anhydride (C 12 O 9 )i sk nown to be stable,s uggesting that Pt 9 C 12 might be generated in an equivalent structural form. An experimental study [26] of AuC n + and CuC n + revealed ion intensities in the mass spectra that are significantly stronger where n = 3t han for clusters of other sizes. [26] Some caution must be exercised in drawing conclusions about the thermodynamic stability of AuC 3 + relative to other cluster sizes from these results.A si nt he present work, the experiment performed by Ticknor et al [26] did not unambiguously distinguish between various factors that contribute to observed spectral intensities.I ti sl ikely that C 3 was generated with as ignificantly higher abundance [19] than C 2 within the expanding gas sample and this may cause the generation of AuC 3 + to be favored over the generation of clusters of other sizes,r egardless of the thermodynamic stability of AuC 3 + .…”

“…An experimental study [26] of AuC n + and CuC n + revealed ion intensities in the mass spectra that are significantly stronger where n = 3t han for clusters of other sizes. [26] Some caution must be exercised in drawing conclusions about the thermodynamic stability of AuC 3 + relative to other cluster sizes from these results.A si nt he present work, the experiment performed by Ticknor et al [26] did not unambiguously distinguish between various factors that contribute to observed spectral intensities.I ti sl ikely that C 3 was generated with as ignificantly higher abundance [19] than C 2 within the expanding gas sample and this may cause the generation of AuC 3 + to be favored over the generation of clusters of other sizes,r egardless of the thermodynamic stability of AuC 3 + . Indeed, during ap revious study,s ignals for NiC 3 + and NiC 6 + were detected in mass spectra with higher intensity than units containing 1, 2, 4, or 5carbon atoms, [27] although the Ni + ion is not isoelectronic and isolobal with O. However,the reported fragmentation behavior of AuC n + is also notable.C lusters where n is odd lose only the metal atom on photodissociation whereas those with an even value of n display an additional loss channel corresponding to the loss of an odd number of carbon atoms.The overall result is that chains (either isolated or attached to the metal ion) containing an odd number of carbon atoms tend to be formed during photofragmentation, consistent with the proposal of Pyykkç et al Theperspective thus emerging from the collected results of spectroscopic experiments is that the proposal [2a] of an autogenic isolobal relationship of Pt and Au + centers with the Oatom is powerful and useful with respect to structural trends in gasphase clusters that contain Pt, Pd, Au + ,and Cc enters.…”