Spectroscopic moments

Substitution by a group with a positive spectroscopic moment ... 

For the enantiomers the respective signs for the contributions are reversed. The signs are the same for the 3,5-disubstituted compounds. cSee Reference 106 for spectroscopic moments. 

Fig. 44. Correlation of low energy shake up intensity accompanying Cls photoionization (for a given parasubstituted polystyrene) with Platts spectroscopic moment and the coulomb intergral of the substituent...

The fact that the parameter ai is connected to spectroscopic moments for absorption and emission transitions opens an interesting opportunity to derive the polarizability change of optical chromophores from spectroscopic first and second moments. The equation for the polarizability change is as follows ... 

In many practical cases, the factors f i are very close to unity and can be omitted. The parameters So, and mo,- are then equal to their gas-phase values oto, and mo,. Equation [100] then gives the polarizability change in terms of spectroscopic moments and gas-phase solute dipoles. Experimental measurement and theoretical calculation of Aao = aoi - ocoi is still challenging. Perhaps the most accurate way to measure Akq presently available is that by Stark spectroscopy,which also gives Awq. Equation [100] can therefore be used as an independent source of Aao, provided all other parameters are available, or as a consistency test for the band shape analysis. 

Systematic studies on disubstituted thiophenes are scarce, but some differences between the various series of disubstituted thiophenes have been detected. According to Imoto et al, the main effect of substituents in 2,5-disubstitution in thiophenes appears in the wavelength shift, whereas the main effect of substituents in the 2,4-disub-stituted thiophenes appears in the intensity changes of the bands. The intensities of the first absorption band of some 2,6-disubstituted thiophenes have been calculated from the spectroscopic moments of the substituents. The UV absorption of thiophene was displaced... 

Table 5.4. Comparison of Ama and Spectroscopic Moments with Orientation...

Thiazyl monomer is a radical with one unpaired electron. In contrast to nitric oxide, it polymerizes so readily that it cannot be isolated as a monomeric solid or liquid and has only a transient existence in the gas phase. Thiazyl monomer may be generated in a number of ways, including the volatilization of (SN) c (2) or pyrolysis of S4N4 (1) over quartz wool above 300 °C. The emission spectrum and ESR spectrum have been reported. The bond length is calculated to be 149.7 pm from its spectroscopic moment of inertia. This indicates a bond order of between two and three. The dissociation energy of this strong sulfur-nitrogen bond is estimated to be 463 kj mol from spectroscopic data. Nevertheless, like other sulfur nitrides, NS is endothermic and unstable with respect to its elements. Thiazyl monomer exhibits an IR band at 1209 cm T The experimental dipole moment is 1.83 0.03 D and the ionization potential is 9.85 eV. 

The electronic and vibrational contributions to secondary band absorptivity are nearly separable (Sklar, 1942). Also, the electronic contributions of the substituents are vector-additive. In fact, for every substituent a migra-tional moment (Sklar, 1942), spectroscopic moment (Platt, 1951) or, more... 

After calibrating the electron wavelength using spectroscopic moments of inertia ... 

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