Dissociation energy spectroscopic constants

The development of comprehensive models for transition metal carbonyl photochemistry requires that three types of data be obtained. First, information on the dynamics of the photochemical event is needed. Which reactant electronic states are involved What is the role of radiationless transitions Second, what are the primary photoproducts Are they stable with respect to unimolecular decay Can the unsaturated species produced by photolysis be spectroscopically characterized in the absence of solvent Finally, we require thermochemical and kinetic data i.e. metal-ligand bond dissociation energies and association rate constants. We describe below how such data is being obtained in our laboratory. 

The spectroscopic dissociation energy D is the dissociation energy of an ideal gas molecule at absolute zero, where all the gas molecules are in the zero potential energy level, h is Planck s constant (6.62 x lO Vrg second), and iv, is the frequency of vibration of the nuclei at the lowest vibrational level, which is above the point of zero potential energy at the equilibrium intemuclear separation. Thus, for the hydrogen molecule. D — 4.476 electron volts, l o = 1.3185 x IO 1 sec1, and since I electron volt = 23.06 kilocalories per mole wc calculate I) using Hq.(21) as... 

In addition to spectroscopic constants Legon et al.88) determined geometrical parameters, dipole moments, dissociation energies and force constants for HCN.HF and a number of its isotopically substituted analogs. 

Two of its three adjustable parameters, De and re correspond to directly measurable molecular properties of bond dissociation energy and equilibrium interatomic distance respectively. The third parameter, a, is related to the force constants commonly used in spectroscopic analyses. A standard procedure [147] to obtain experimental potential energy curves is to calculate from spectroscopic data the constants ke, g, and j that appear in the expression... 

The resonance Raman spectra of Fe2, NiFe, Vz, T 2 and Ni3 in solid, rare-gas matrices are reviewed. Spectroscopic constants for these were (WgjtOgXg, cm ) Fe2 (300.26, 1.45), NiFe (320.0, 1.32), V2 (508.0, 3.3) and Ti2 (407.9, 1.08). A Bernstein-LeRoy analysis was performed on the data for Fe2, yielding a bond dissociation energy of 1.2 eV, close to that reported by Kant. All of the transition metal diatomlcs studied showed an Inordinate ability to remain vibrationally excited when the first few vibrational levels were populated radiatively. This gave rise to intense antistokes... 

The G(v), By and D spectroscopic constants for the ground state and the dissociation energy were determined by Colbourn et al. (J[ ). These are used in the computation as given (and not as the usual fitting coefficients jo, etc.). The rotational... 

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