where r is the variable interatomic
distance and reis the equilibrium in-
teratomic distance. The Morse poten-
tial U(r – re) is given by
De{1 – exp[–β(–r – re)]}^2 ,
where Deis the dissociation energy at
the minimum of the curve (i.e. when
r = re) and βis a constant. The Morse
potential was used by the US physi-
cist Philip M. Morse in 1929 in solv-
ing 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 im-
prove on this aspect.mosaic goldSee 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 el-
ements 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 agateSee agate.
Mössbauer effect An effect occur-
ring 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 en-
ergy of the process is partitioned be-
tween 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 lat-tice. Since this may typically contain
1010 –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 Möss-
bauer spectroscopyin which a
gamma-ray source is mounted on a
moving platform and a similar sam-
ple is mounted nearby. A detector
measures gamma rays scattered by
the sample. The source is moved
slowly towards the sample at a vary-
ing speed, so as to continuously
change the frequency of the emitted
gamma radiation by the Doppler ef-
fect. A sharp decrease in the signal
from the detector at a particular
speed (i.e. frequency) indicates reso-
nance absorption in the sample nu-
clei. 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 en-
ergy are produced by the presence of
surrounding atoms.m.p.See melting point.
MSGSee monosodium glutamate.mucopolysaccharideSee gly-
cosaminoglycan.
mufÛe furnace An insulated fur-
nace, usually electrically heated, used
for producing controlled high tem-
peratures. In the laboratory, mufÛe
furnaces are used for drying solids,
sintering, and studying high-temper-
ature reactions. They typically oper-
ate 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 *bo-
ranes can be explained by consider-
ing them to be *electron-deÜcient
compounds containing multicentre
bonds.mosaic gold 362m