Vibrational spectra are measured for Fe(CH) (n = 1-3) and Fe(CH) in the C-H stretching region (2650-3100 cm) using photofragment spectroscopy, monitoring loss of CH. All of the spectra are dominated by an intense peak at around 2800 cm that is red-shifted by ∼120 cm from free methane. This peak is due to the symmetric C-H stretch of the η hydrogen-coordinated methane ligands. For clusters with three iron atoms, the peak becomes less red-shifted as the number of methane ligands increases. For clusters with one methane ligand per iron atom, the red shift increases in going from Fe(CH) (88 cm) to Fe(CH) (108 cm) to Fe(CH) (122 cm). This indicates increased covalency in the binding of methane to the larger iron clusters and parallels their increased reactivity. Density functional theory calculations, B3LYP, BPW91, and M11L, are used to identify possible structures and geometries and to predict the spectra. Results show that all three functionals tend to overestimate the methane binding energies. The M11L calculations provide the best match to the experimental spectra.
While limited by the small sample sizes in the included trials, this analysis suggests that the early benefit of EVBT is counter-balanced by the increased risk of new lesions and the lack of medium- to long-term reductions in restenosis risk. Based upon the best available evidence, EVBT cannot be recommended for routine clinical use.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.