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Pure Appl. Chem., Vol. 68, No.12, pp. 2223-2286, 1996

Glossary of Terms Used in Photochemistry


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ODMR (Optically Detected Magnetic Resonance)
A double resonance technique in which transitions between spin sublevels are detected by optical means. Usually these are sublevels of a triplet and the transitions are induced by microwaves. For different types of optical detection (as explained) the following expressions are used: ADMR (absorption), DEDMR (delayed emission, nonspecified), DFDMR (delayed fluorescence), FDMR (fluorescence), PDMR (phosphorescence). If a reaction yield is monitored the expression RYDMR (reaction yield detected magnetic resonance) is used.

OPTICAL DENSITY
Synonymous with absorbance. The use of the term optical density is discouraged.

OPTOACOUSTIC SPECTROSCOPY
Same as photoacoustic spectroscopy.

ORBITAL (Atomic or Molecular)

A wavefunction which depends explicitly on the spatial coordinates of only one electron.

OSCILLATOR STRENGTH (f Number)
A measure of the intensity of a spectral band: a classical concept (giving the effective number of electrons taking part in a certain transition) adapted to wave mechanics. For a transition between state i and state j,

where m is the mass of the electron, c the velocity of light, nu the frequency, h the Planck constant, G the degeneracy of the final state. Rij is the transition moment calculated omitting e, the electron charge, in the integral; better called the transition length. Experimentally, fij is determined by integration of the absorption band, using the equation

where epsilon(sigma) is the molar absorption coefficient at wavenumber sigma and n the average refractive index of the medium. k = 4.32 x 10, -9 L-1 mol cm (for epsilon in the common units L mol-1 cm-1); k = 4.32 x 10-8 mol m-1 (for epsilon in SI unit m2mol-1). The oscillator strength, fij , is a dimensionless quantity.

See also transition (dipole) moment.

OUTER-SPHERE ELECTRON TRANSFER
Electron transfer between redox centers which do not share a common atom or group, i.e. , the interaction between the relevant electronic orbitals of the two centers in the transition state is weak (< 20 kJ mol-1).

Compare inner-sphere electron transfer

OXA-DI-pi-METHANE REARRANGEMENT
A photochemical reaction of beta, gamma-unsaturated ketone to form a saturated alpha-cyclopropyl ketone. The rearrangement formally amounts to a 1,2-acyl shift and "bond formation" between the former alpha and gamma carbon atoms.

See also di-pi-methane rearrangement.




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Online version compiled by European Photochemistry Association (EPA)

 

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