electromagnetic coupling to one of
the bound electrons of that atom
rather than being released as a photon. The coupling is usually with an
electron in the K-, L-, or M-shell of
the atom, and this conversion electron is ejected from the atom with a
kinetic energy equal to the difference
between the nuclear transition energy and the binding energy of the
electron. The resulting ion is itself in
an excited state and usually subsequently emits an Auger electron or
an X-ray photon.
internal energy Symbol U. The
total of the kinetic energies of the
atoms and molecules of which a system consists and the potential energies associated with their mutual
interactions. It does not include the
kinetic and potential energies of the
system as a whole nor their nuclear
energies or other intra-atomic energies. The value of the absolute internal energy of a system in any
particular state cannot be measured;
the signiÜcant quantity is the change
in internal energy, ∆U. For a closed
system (i.e. one that is not being replenished from outside its boundaries) the change in internal energy
is equal to the heat absorbed by the
system (Q) from its surroundings, less
the work done (W) by the system on
its surroundings, i.e. ∆U = Q – W. See
also energy; thermodynamics.
internal resistance The resistance
within a source of electric current,
such as a cell or generator. It can be
calculated as the difference between
the e.m.f. (E) and the potential difference (V) between the terminals divided by the current being supplied
(I), i.e. r = (E – V)/I, where r is the internal resistance.
interstellar molecules See astrochemistry.
interstellar molecules See astrochemistry.
interstitial See crystal defect.
interstitial compound A compound in which ions or atoms of a
nonmetal occupy interstitial positions in a metal lattice. Such compounds often have metallic
properties. Examples are found in
the *carbides, *borides, and *silicides.
intersystem crossing A process in
which a singlet excited electronic
state makes a transition to a triplet
excited state at the point where the
potential energy curves for the excited singlet and triplet states cross.
This transition is forbidden in the absence of *spin–orbit coupling but occurs in the presence of spin–orbit
coupling. A triplet formed in this
way is frequently in an excited vibrational state. This excited triplet state
can reach its lowest vibrational state
by collisions with other molecules.
The transition from this state to the
singlet state is forbidden in the absence of spin–orbit coupling but allowed when there is spin–orbit
coupling. This gives rise to the slow
emision of electromagnetic radiation
known as *phosphorescence.
intrinsic factor See vitamin b complex.
Invar A tradename for an alloy of
iron (63.8%), nickel (36%), and carbon
(0.2%) that has a very low expansivity
over a a restricted temperature
range. It is used in watches and other
instruments to reduce their sensitivity to changes in temperature.
inverse Compton effect The gain
in energy of low-energy photons
when they are scattered by free electrons of much higher energy. As a
consequence, the electrons lose energy. See also compton effect.
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inverse Compton effect
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the bound electrons of that atom
rather than being released as a photon. The coupling is usually with an
electron in the K-, L-, or M-shell of
the atom, and this conversion electron is ejected from the atom with a
kinetic energy equal to the difference
between the nuclear transition energy and the binding energy of the
electron. The resulting ion is itself in
an excited state and usually subsequently emits an Auger electron or
an X-ray photon.
internal energy Symbol U. The
total of the kinetic energies of the
atoms and molecules of which a system consists and the potential energies associated with their mutual
interactions. It does not include the
kinetic and potential energies of the
system as a whole nor their nuclear
energies or other intra-atomic energies. The value of the absolute internal energy of a system in any
particular state cannot be measured;
the signiÜcant quantity is the change
in internal energy, ∆U. For a closed
system (i.e. one that is not being replenished from outside its boundaries) the change in internal energy
is equal to the heat absorbed by the
system (Q) from its surroundings, less
the work done (W) by the system on
its surroundings, i.e. ∆U = Q – W. See
also energy; thermodynamics.
internal resistance The resistance
within a source of electric current,
such as a cell or generator. It can be
calculated as the difference between
the e.m.f. (E) and the potential difference (V) between the terminals divided by the current being supplied
(I), i.e. r = (E – V)/I, where r is the internal resistance.
interstellar molecules See astrochemistry.
interstellar molecules See astrochemistry.
interstitial See crystal defect.
interstitial compound A compound in which ions or atoms of a
nonmetal occupy interstitial positions in a metal lattice. Such compounds often have metallic
properties. Examples are found in
the *carbides, *borides, and *silicides.
intersystem crossing A process in
which a singlet excited electronic
state makes a transition to a triplet
excited state at the point where the
potential energy curves for the excited singlet and triplet states cross.
This transition is forbidden in the absence of *spin–orbit coupling but occurs in the presence of spin–orbit
coupling. A triplet formed in this
way is frequently in an excited vibrational state. This excited triplet state
can reach its lowest vibrational state
by collisions with other molecules.
The transition from this state to the
singlet state is forbidden in the absence of spin–orbit coupling but allowed when there is spin–orbit
coupling. This gives rise to the slow
emision of electromagnetic radiation
known as *phosphorescence.
intrinsic factor See vitamin b complex.
Invar A tradename for an alloy of
iron (63.8%), nickel (36%), and carbon
(0.2%) that has a very low expansivity
over a a restricted temperature
range. It is used in watches and other
instruments to reduce their sensitivity to changes in temperature.
inverse Compton effect The gain
in energy of low-energy photons
when they are scattered by free electrons of much higher energy. As a
consequence, the electrons lose energy. See also compton effect.
287
inverse Compton effect
i
www.AzShimi.ir www.AzShimi.com