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..!!!