The far-infrared spectra of neutral and cationic niobium clusters: Nb5∕+ to Nb9∕+

Abstract

Far-infrared absorption spectra of small neutral and cationic niobium clusters containing five to nine Nb atoms have been obtained by multiple photon dissociation spectroscopy of their argon complexes. The experimental far-IR spectra are recorded in the 85-600 cm −1 region and cover the range of the structure-specific vibrational fundamentals, i.e., the finger-print range, for these metal clusters. The experiments are accompanied by quantum chemical calculations employing the density-functional theory. A comparison of the experimental and calculated far-IR spectra allows to identify the cluster structures. Although the experimental spectra for clusters containing five, six, eight, and nine Nb atoms are very different for cationic and neutral clusters, the comparison with theory reveals that, nevertheless, the overall geometries for cations and neutrals are very similar, except for Nb 6 0/+ .

Probing the structures of gas-phase rhodium cluster cations by far-infrared spectroscopy

“…Therefore, isomerization would be expected to occur more rapidly in our experiment. While it is not certain that the neutral and cationic cluster PELs are the same, 44,60 this supports our interpretation of the presence of multiple isomers of Rh + 10 and the possibility of isomerization occurring on timescales similar to, or shorter than, that of the experiment. Figure 8 shows the comparison of the experimental and calculated spectra of Rh + 11 .…”

Onset of carbon–carbon bonding in the Nb5Cy(y = 0–6) clusters: a threshold photo-ionisation and density functional theory study

“…Recent IR multi-photon dissociation (IR-MPD) experiments with an IR-FEL on Nb 5 -Ar and Nb + 5 -Ar are consistent with these calculated results. 32 Before the isomeric structures of the Nb 5 C y clusters are discussed, it is useful to describe the geometries the underlying Nb 5 motif may have in these clusters. Analogous to the lowest energy Nb 5 structure there is the prolate ''trigonal bipyramid'' geometry where the two axial Nb atoms are at a longer distance to the centre of mass than the three equatorial Nb atoms.…”

Nature of Ar bonding to small Con+ clusters and its effect on the structure determination by far-infrared absorption spectroscopy

“…14 A negligible influence of the raregas atoms was indeed inferred from insignificant differences in the IR-spectra of previously studied cationic V + n (n = 3 − 23) 9,10 , Nb + n (n = 5 − 9) 11,12 and Ta + n (n = 6 − 20) 13 complexes that contained one or more Ar atoms. Restricted test calculations comparing the IRspectra of bare and Ar-complexed V + 3 and V + 4 clusters led to the same conclusion 9,10 , so that the theoretical modeling for the mentioned systems focused exclusively on the IR spectra of the bare metal clusters.…”

“…16 The molecular-beam machine has been presented previously 10,12,14 and only a brief description is given here. Metal clusters are produced by pulsed laser ablation of a cobalt rod using the 2 nd harmonic output of a Nd:YAG laser and by subsequent condensation of the plasma in a mixture of Ar in He.…”

“…A corresponding technique that has recently been successfully employed to determine the structure of cationic and neutral metal clusters containing between three and 20 atoms is far-infrared (vibrational) resonance enhanced multiple photon dissociation (FIR-MPD) spectroscopy. 9,10,11,12,13 The essential idea of this technique is to irradiate rare-gas complexes of the targeted clusters with infrared (IR) light in the range of the structure-specific vibrational fundamentals. When the IR light is resonant with a vibrational mode in the cluster complex, the complex can absorb several photons and subsequently evaporate off one or more rare-gas atoms.…”