J
Jablonski diagram A diagram
that represents the electronic energy
levels (and their relative positions) of
a molecule. A Jablonski diagram enables radiative transitions between
energy levels in molecules, as well as
such phenomena as internal conversion, to be shown. The vertical axis
measures energy, with the electronic
energy levels in their lowest vibrational states being short horizontal
lines. The vibrational energy levels of
a particular electronic state are
drawn as shaded regions above the
horizontal line for that state. In a
Jablonski diagram the horizontal location of the electronic state is not
related to the internuclear distance
between the atoms in these states.
jacinth See zircon.
jade A hard semiprecious stone
consisting either of jadeite or
nephrite. Jadeite, the most valued of
the two, is a sodium aluminium pyroxene, NaAlSi 2 O 6 . It is prized for its
intense translucent green colour but
white, green and white, brown, and
orange varieties also occur. The only
important source of jadeite is in the
Mogaung region of upper Burma.
Nephrite is one of the amphibole
group of rock-forming minerals. It
occurs in a variety of colours, including green, yellow, white, and black.
Sources include the Siberia, Turkistan, New Zealand, Alaska, China,
and W USA.
jadeite See jade.
Jahn–Teller effect If a likely structure of a nonlinear molecule or ion
would have degenerate orbitals (i.e.
two molecular orbitals with the same
energy levels) the actual structure of
the molecule or ion is distorted so as
to split the energy levels (‘raise’ the
degeneracy). The effect is observed in
inorganic complexes. For example,
the ion [Cu(H 2 O) 6 ]
2+ is octahedral and
the six ligands might be expected to
occupy equidistant positions at the
corners of a regular octahedron. In
fact, the octahedron is distorted,
with four ligands in a square and two
opposite ligands further away. If the
‘original’ structure has a centre of
symmetry, the distorted structure
must also have a centre of symmetry.
The effect was predicted theoretically
by H. A. Jahn (1907–79) and Edward
Teller (1908–2003) in 1937.
jargoon See zircon.
jasper An impure variety of *chalcedony. It is associated with iron ores
and as a result contains iron oxide
impurities that give the mineral its
characteristic red or reddish-brown
colour. Jasper is used as a gemstone.
jet A variety of *coal that can be cut
and polished and is used for jewellery, ornaments, etc.
jeweller’s rouge Red powdered
haematite, iron(III) oxide, Fe 2 O 3 . It is
a mild abrasive used in metal cleaners and polishes.
j-j coupling A type of *coupling occurring between electrons in atoms
and nucleons in nuclei, in which
the energies associated with the
spin–orbit interactions are much
higher than the energies associated
with electrostatic repulsion. *Multiplets of many-electron atoms having
a large atomic number are characterwww.AzShimi.ir www.AzShimi.com
Jablonski diagram A diagram
that represents the electronic energy
levels (and their relative positions) of
a molecule. A Jablonski diagram enables radiative transitions between
energy levels in molecules, as well as
such phenomena as internal conversion, to be shown. The vertical axis
measures energy, with the electronic
energy levels in their lowest vibrational states being short horizontal
lines. The vibrational energy levels of
a particular electronic state are
drawn as shaded regions above the
horizontal line for that state. In a
Jablonski diagram the horizontal location of the electronic state is not
related to the internuclear distance
between the atoms in these states.
jacinth See zircon.
jade A hard semiprecious stone
consisting either of jadeite or
nephrite. Jadeite, the most valued of
the two, is a sodium aluminium pyroxene, NaAlSi 2 O 6 . It is prized for its
intense translucent green colour but
white, green and white, brown, and
orange varieties also occur. The only
important source of jadeite is in the
Mogaung region of upper Burma.
Nephrite is one of the amphibole
group of rock-forming minerals. It
occurs in a variety of colours, including green, yellow, white, and black.
Sources include the Siberia, Turkistan, New Zealand, Alaska, China,
and W USA.
jadeite See jade.
Jahn–Teller effect If a likely structure of a nonlinear molecule or ion
would have degenerate orbitals (i.e.
two molecular orbitals with the same
energy levels) the actual structure of
the molecule or ion is distorted so as
to split the energy levels (‘raise’ the
degeneracy). The effect is observed in
inorganic complexes. For example,
the ion [Cu(H 2 O) 6 ]
2+ is octahedral and
the six ligands might be expected to
occupy equidistant positions at the
corners of a regular octahedron. In
fact, the octahedron is distorted,
with four ligands in a square and two
opposite ligands further away. If the
‘original’ structure has a centre of
symmetry, the distorted structure
must also have a centre of symmetry.
The effect was predicted theoretically
by H. A. Jahn (1907–79) and Edward
Teller (1908–2003) in 1937.
jargoon See zircon.
jasper An impure variety of *chalcedony. It is associated with iron ores
and as a result contains iron oxide
impurities that give the mineral its
characteristic red or reddish-brown
colour. Jasper is used as a gemstone.
jet A variety of *coal that can be cut
and polished and is used for jewellery, ornaments, etc.
jeweller’s rouge Red powdered
haematite, iron(III) oxide, Fe 2 O 3 . It is
a mild abrasive used in metal cleaners and polishes.
j-j coupling A type of *coupling occurring between electrons in atoms
and nucleons in nuclei, in which
the energies associated with the
spin–orbit interactions are much
higher than the energies associated
with electrostatic repulsion. *Multiplets of many-electron atoms having
a large atomic number are characterwww.AzShimi.ir www.AzShimi.com