nmr ppt
DESCRIPTION
Analytical InstrumentationTRANSCRIPT
NUCLEAR
MAGNETIC
RESONANCE
(NMR)
SPECTROMETER
-- PRIYA SRIVASTAVA 090105801 EIE, VI SEM.
BASIC:
Nuclear Magnetic
Resonance spectroscopy
is a NDT.
For mapping molecular
structures & learning how
molecules function &
relate to each other.
It is recognized as
one of the most powerful techniques for
chemical analysis.
The study of absorption of
radiofrequency radiation by nuclei in
a magnetic field is called Nuclear
Magnetic Resonance.
UTILITIES & IMPORTANCE
The importance of this technique is reflected in the efforts that have
been made to extent its applicability to smaller & smaller
sample sizes.
The utility of this is for structural characterization arises because different atoms in a molecule experience slightly different
magnetic fields.
PRINCIPLES
Nuclear Spin
Elementary particles such as electrons or a nucleus are known to behave as if they rotate about an axis & thus have the property
of spin.
The angular momentum
associated with the spin of the
particle would be an integral or a
half-integral multiple of h/2pi.
Nuclear Energy Levels
Since a nucleus possesses a charge, its spin gives rise to a
magnetic field that is analogous to the field
produced when an electric current is passed through a
coil of wire.
When a spinning nucleus is placed in a strong uniform magnetic field(H), the field exerts a torque upon the
nuclear magnet.
Resonance Conditions
When an alternating radiofrequency field, superimposed over the stationary
magnetic field, rotates at exactly the frequency of an energy level, the nuclei
will be provided enough energy to undergo a transition from a lower energy
level to a higher energy level.
In general, the energy difference b/w states is given by:
RELAXATION PROCESS
When nuclei in the higher energy state return to the lower state,
emission of radiation takes place. There are two major R.P-
1.Spin-lattice(longitudinal)2.Spin-Spin(transverse)
However, the emission is insignificant because the probability
of re-emission of photons varies with the cube of the frequency. At radio-frequencies, re-emission is
negligible.
The Chemical
shift
The difference b/w the field necessary for resonance in the sample &
in some arbitrarily
chosen reference
compound is called the ‘Chemical
Shift’.
It is expressed
as:
TYPES
Continuous-Wave NMR Spectroscopy
A CW-NMR spectrometer consists of a control console, magnet, & two orthogonal coils of wire that serve as
antennas for radiofrequency radiation.
One coil is attached to an rf generator & serves as a transmitter.
The other coil is the rf pick-up coil & is attached to the detection electronics.
Fourier Transform NMR Spectroscopy
It use a pulse of rf radiaiton which causes nuclei in a magnetic field to flip into the higher energy
alignment.
Due to Heisenberg uncertainty principle, the frequency width of the rf pulse is wide enough to
simultaneously excite nuclei in environment.
All the nuclei will re-emit rf radiation at their respective resonance frequencies, creating an
interference pattern in the resulting rf emission vs. time, known as FID(Free Induction Decay)
CONSTRUCTIONAL DETAILS
The key parts of the system are:-
A magnet which produces a magneitc field in the range 10,000-25,000 gauss,
Radio-frequency transmitting system,
The signal amplifier & detector,
A display device,
A non-magnetic sample holder
Computer workstation
ELECTRON SPIN RESONANCE SPECTROMETERS
It involves detecting the detection of a physical
phenomenon of absorption of electromagnetic
radiation in the microwave region by paramagnetic
species that are subjected to an external magnetic
field.
It is the study of magnetic dipoles of electronic origin by applying, usually fixed
microwave frequencies to a sample residing in a varying
magnetic field.
DETAILED DESCRIPTION OF ESR SPECTROMRTER
INSTRUMENTATION FOR E.S
It contains the following
components:
A source of radiation with which to excite
the sample.
An electron energy analyzer,
An electron detector
A read-out system, &
A high vacuum system
INSTRUMENTATION FOR X-RAY SPECTROMETRY
THE IMPORTANT PARTS ARE:-
X-ray generating equipment,
Collimator,
Monochromators, and
Detectors
THANKS… FOR YOUR PATIENCE..!!!