Interaction with External Fields
201
(see Fig. 6.9 ) with the technique known as in vivo magnetic resonance
spectroscopy or chemical shift NMR Microscopy.
Fig. 6.9 Medical MRI.
Raman Effect
It was observed in 1928, by Raman and Krishnan, and simultaneously by
Landsberg and Mandelshtam, that the spectrum of light scattered by gases, liquids
and crystals, contains apart from the unshifted original frequency ω, new lines
whose frequencies are given by
ω′ = ω ± ω 1
(6.103)
This is known as Raman effect, or more descriptively, as combination
scattering of light.
The process of scattering of radiation may be regarded as being made up of
absorption of the incoming photon and emission of the outgoing photon. If, as
a result, the final state of the atom or molecule is the same as the initial state, the
frequency of the photon is unchanged, giving the unshifted line. This process is
known as Rayleigh scattering. On the other hand, if the final state of the atom
or molecule is different, the process is an inelastic scattering of the photon and
the frequency ω′ of the final photon is given by the energy conservation relation
ω + E′ = E + ω
(6.104)
or
ω′ =
E E
− ′
ω +
(6.105)
The shifted frequency is less than the original frequency if E < E′ and the
corresponding lines are called the Stokes lines. It is more than the original
frequency if E > E′ and the associated lines are called the anti-Stokes lines. At
ordinary temperatures, there are more particles in the lower energy states, so
that there are more transitions with E 1 → E 2 than those with E 2 → E 1 , E 2 > E 1 .
Therefore, anti-Stokes lines are generally fainter (in some cases not even
observable) than the Stokes lines. The anti-Stokes lines increase in intensity as
the temperature is raised since this will increase the relative population of the
higher energy states.
201
(see Fig. 6.9 ) with the technique known as in vivo magnetic resonance
spectroscopy or chemical shift NMR Microscopy.
Fig. 6.9 Medical MRI.
Raman Effect
It was observed in 1928, by Raman and Krishnan, and simultaneously by
Landsberg and Mandelshtam, that the spectrum of light scattered by gases, liquids
and crystals, contains apart from the unshifted original frequency ω, new lines
whose frequencies are given by
ω′ = ω ± ω 1
(6.103)
This is known as Raman effect, or more descriptively, as combination
scattering of light.
The process of scattering of radiation may be regarded as being made up of
absorption of the incoming photon and emission of the outgoing photon. If, as
a result, the final state of the atom or molecule is the same as the initial state, the
frequency of the photon is unchanged, giving the unshifted line. This process is
known as Rayleigh scattering. On the other hand, if the final state of the atom
or molecule is different, the process is an inelastic scattering of the photon and
the frequency ω′ of the final photon is given by the energy conservation relation
ω + E′ = E + ω
(6.104)
or
ω′ =
E E
− ′
ω +
(6.105)
The shifted frequency is less than the original frequency if E < E′ and the
corresponding lines are called the Stokes lines. It is more than the original
frequency if E > E′ and the associated lines are called the anti-Stokes lines. At
ordinary temperatures, there are more particles in the lower energy states, so
that there are more transitions with E 1 → E 2 than those with E 2 → E 1 , E 2 > E 1 .
Therefore, anti-Stokes lines are generally fainter (in some cases not even
observable) than the Stokes lines. The anti-Stokes lines increase in intensity as
the temperature is raised since this will increase the relative population of the
higher energy states.