Ultraviolet-Visible SpectroscopyMeasurement of transmittance
Conversion to absorbance
A=-logT=ebc
Beer’s law
Contains only solvent
Measurement for transmittance is compared to results from reference cell
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dPx/Px=dS/S
Proportional to number of absorbing particles
dS=adn
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S=V/b (cm2)
Substitute for S
Beer’s law can be applied to mixtures
Atot=SAx
Photon detector shot noise
Widely used method
e=8.7E19PA
Forbidden transition 0.01
Relaxation processes
d and f electrons
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Methane at 125 nm
Ethane at 135 nm
Absorption between 150 nm to 250 nm
e between 100 and 3000 L cm-1 mol-1
Shifts to shorter wavelengths with polar solvents
Minimum accessibility
Requires unsaturated groups
Shorter wavelengths
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Broad transitions
similar
Binding ligands on axis have greater effect on axial orbitals
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D value dependent upon ligand field strength
<Br-<Cl-<F-<OH-<C2O42-~H2O<SCN-<NH3<en<NO2-<CN-
D increases with increasing field strength
f-f
Sharper transitions
Actinide transitions
Figure 2: UV-vis spectra of organic phases for 13M HNO3 system
8.bin
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Absorption involves e- transitions from donor to acceptor
SCN to Fe(III)
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CT at higher energy
Ligand to metal transition
Electron moves between orbitals
Lone pair ligand donor
pH, ligand, metal