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,
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 ()
is the molar absorption coefficient at wavenumber
and n the average refractive index of the medium. k = 4.32 x 10, -9
L-1 mol cm (for
in the common units L mol-1 cm-1); k = 4.32
x 10-8 mol m-1 (for
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--METHANE
REARRANGEMENT
A photochemical reaction of ,
-unsaturated
ketone to form a saturated -cyclopropyl
ketone. The rearrangement formally amounts to a 1,2-acyl shift and
"bond formation" between the former
and
carbon atoms.
See also di--methane
rearrangement.