where r is the variable interatomic
distance and r e is the equilibrium interatomic distance. The Morse potential U(r – r e ) is given by
D e {1 – exp[–β(–r – r e )]}
2 ,
where D e is the dissociation energy at
the minimum of the curve (i.e. when
r = r e ) and β is a constant. The Morse
potential was used by the US physicist Philip M. Morse in 1929 in solving the Schrödinger equation. The
Morse potential is a reasonably good
representation of a potential-energy
function except that as r approaches
0, U does not approach inÜnity as it
should for a true potential energy
function. ModiÜcations of the Morse
potential have been suggested to improve on this aspect.
mosaic gold See tin(iv) sulphide.
Moseley’s law The frequencies of
the lines in the *X-ray spectra of the
elements are related to the atomic
numbers of the elements. If the
square roots of the frequencies of
corresponding lines of a set of elements are plotted against the
atomic numbers a straight line is
obtained. The law was discovered by
H. G. Moseley (1887–1915).
A
• Original paper on the law
moss agate See agate.
Mössbauer effect An effect occurring when certain nuclides decay
with emission of gamma radiation.
For an isolated nucleus, the gamma
radiation would usually have a
spread of energies because the energy of the process is partitioned between the gamma-ray photon and
the recoil energy of the nucleus. In
1957 Rudolph Mössbauer (1929– )
found that in certain solids, in which
the emitting nucleus is held by
strong forces in the lattice, the recoil
energy is taken up by the whole lattice. Since this may typically contain
10
10 –10
20 atoms, the recoil energy is
negligible and the energy of the
emitted photon is sharply deÜned in
a very narrow energy spread.
The effect is exploited in Mössbauer spectroscopy in which a
gamma-ray source is mounted on a
moving platform and a similar sample is mounted nearby. A detector
measures gamma rays scattered by
the sample. The source is moved
slowly towards the sample at a varying speed, so as to continuously
change the frequency of the emitted
gamma radiation by the Doppler effect. A sharp decrease in the signal
from the detector at a particular
speed (i.e. frequency) indicates resonance absorption in the sample nuclei. The effect is used to investigate
nuclear energy levels. In chemistry,
Mössbauer spectroscopy can also give
information about the bonding and
structure of compounds because
chemical shifts in the resonance energy are produced by the presence of
surrounding atoms.
m.p. See melting point.
MSG See monosodium glutamate.
mucopolysaccharide See glycosaminoglycan.
mufÛe furnace An insulated furnace, usually electrically heated, used
for producing controlled high temperatures. In the laboratory, mufÛe
furnaces are used for drying solids,
sintering, and studying high-temperature reactions. They typically operate in the range 100–1200°C.
multicentre bond A bond formed
between three, and sometimes more,
atoms that contains only a single pair
of electrons. The structure of *boranes can be explained by considering them to be *electron-deÜcient
compounds containing multicentre
bonds.
mosaic gold
362
m
www.AzShimi.ir www.AzShimi.com
distance and r e is the equilibrium interatomic distance. The Morse potential U(r – r e ) is given by
D e {1 – exp[–β(–r – r e )]}
2 ,
where D e is the dissociation energy at
the minimum of the curve (i.e. when
r = r e ) and β is a constant. The Morse
potential was used by the US physicist Philip M. Morse in 1929 in solving the Schrödinger equation. The
Morse potential is a reasonably good
representation of a potential-energy
function except that as r approaches
0, U does not approach inÜnity as it
should for a true potential energy
function. ModiÜcations of the Morse
potential have been suggested to improve on this aspect.
mosaic gold See tin(iv) sulphide.
Moseley’s law The frequencies of
the lines in the *X-ray spectra of the
elements are related to the atomic
numbers of the elements. If the
square roots of the frequencies of
corresponding lines of a set of elements are plotted against the
atomic numbers a straight line is
obtained. The law was discovered by
H. G. Moseley (1887–1915).
A
• Original paper on the law
moss agate See agate.
Mössbauer effect An effect occurring when certain nuclides decay
with emission of gamma radiation.
For an isolated nucleus, the gamma
radiation would usually have a
spread of energies because the energy of the process is partitioned between the gamma-ray photon and
the recoil energy of the nucleus. In
1957 Rudolph Mössbauer (1929– )
found that in certain solids, in which
the emitting nucleus is held by
strong forces in the lattice, the recoil
energy is taken up by the whole lattice. Since this may typically contain
10
10 –10
20 atoms, the recoil energy is
negligible and the energy of the
emitted photon is sharply deÜned in
a very narrow energy spread.
The effect is exploited in Mössbauer spectroscopy in which a
gamma-ray source is mounted on a
moving platform and a similar sample is mounted nearby. A detector
measures gamma rays scattered by
the sample. The source is moved
slowly towards the sample at a varying speed, so as to continuously
change the frequency of the emitted
gamma radiation by the Doppler effect. A sharp decrease in the signal
from the detector at a particular
speed (i.e. frequency) indicates resonance absorption in the sample nuclei. The effect is used to investigate
nuclear energy levels. In chemistry,
Mössbauer spectroscopy can also give
information about the bonding and
structure of compounds because
chemical shifts in the resonance energy are produced by the presence of
surrounding atoms.
m.p. See melting point.
MSG See monosodium glutamate.
mucopolysaccharide See glycosaminoglycan.
mufÛe furnace An insulated furnace, usually electrically heated, used
for producing controlled high temperatures. In the laboratory, mufÛe
furnaces are used for drying solids,
sintering, and studying high-temperature reactions. They typically operate in the range 100–1200°C.
multicentre bond A bond formed
between three, and sometimes more,
atoms that contains only a single pair
of electrons. The structure of *boranes can be explained by considering them to be *electron-deÜcient
compounds containing multicentre
bonds.
mosaic gold
362
m
www.AzShimi.ir www.AzShimi.com