Transition metal diatomic molecules

Calculated vs. Experimental Data for Transition Metal Diatomic Molecules... 

Hanlan LA, Ozin GA (1974) Synthesis using transition metal diatomic molecules. Dirhodium octacarbonyl and diiridium octacarbonyl. J Am Chem Soc 96(20) 6324—6329... 

In this paper we will present some examples of the application of resonance Raman spectroscopy to the study of transition metal diatomics. The application of Raman spectroscopy to matrix-isolated metal clusters was first reported by Schulze et al. (] ). Having observed only a single line in the Raman spectrum of Ag3, Schulze concluded that the molecule was linear since a bent triatomic and an equilateral triangular geometry would have, in principle, 3 and 2 Raman-active modes. The evidence, however, is not conclusive since many Czy molecules have very weak asymmetric stretches in the Raman ( ) (for example, the V3 mode of O3 is undetectable in the Raman (3 )). Moreover, the bend (V2) of Ag3 is expected to be a very low-frequency mode, perhaps lower than one can feasibly detect in a matrix Raman experiment. 

Recent experimental data on the transition-metal diatomics is used to test the "isoelectronic" principle as applied to molecules with the same number of d + s valence electrons. Electron configurations auid ground states in the first-row transition-metal monocarbonyl molecules (MCO) are examined on the basis of their CO stretching frequencies, ESR evidence, auid theoretical calculations. 

Unlike nitric oxide, NO, the monomeric radical sulfur nitride, NS, is only known as a short-lived intermediate in the gas phase. Nevertheless the properties of this important diatomic molecule have been thoroughly investigated by a variety of spectroscopic and other physical techniques (Section 5.2.1). The NS molecule is stabilized by coordination to a transition metal and a large number of complexes, primarily with metals from Groups 6, 7, 8 and 9, are known. Several detailed reviews of the topic have been published. ... 

Table 2. Dissociation energies of diatomic transition metal, molecules, Dq(M-M) kj mol-1...

The second contribution on the right-hand side is the shift in the on site energy due to the neighbouring atomic potentials. In the spirit of our earlier treatment of diatomic molecules we will neglect this crystal field term. It does not fundamentally alter the band structure of either transition metals or semiconductors. The band structure, E(k), can, therefore, be written within the approximation as... 

In the following, we will discuss a number of different adsorption systems that have been studied in particular using X-ray emission spectroscopy and valence band photoelectron spectroscopy coupled with DFT calculations. The systems are presented with a goal to obtain an overview of different interactions of adsorbates on surfaces. The main focus will be on bonding to transition metal surfaces, which is of relevance in many different applications in catalysis and electrochemistry. We have classified the interactions into five different groups with decreasing adsorption bond strength (1) radical chemisorption with a broken electron pair that is directly accessible for bond formation (2) interactions with unsaturated it electrons in diatomic molecules (3) interactions with unsaturated it electrons in hydrocarbons ... 

Figure 4.25. Side and top views of the calculated transition state structures for different diatomic molecules dissociating on different close-packed (top) and stepped (bottom) metal surfaces. Adapted from Ref. [80].

At this point photoionization cross sections have been computed mostly for diatomic molecules, rr-electron systems, and other relatively small molecules [see Rabalais (242) for a summary of this work up to 1976]. Very few photoionization cross section calculations have been performed (108) on transition metal systems and the agreement with experimental intensities is rather poor. For the most part, therefore, one must rely on empirical trends when dealing with the photoionization of metal-containing molecules. A number of such trends have now emerged and are useful for spectral assignment. 

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