SPECTROSCOPY

1
SPECTROSCOPY
2
Textbook and reference

• Textbook
• Kenneth A Rubinson Judith F Rubinson,
  Contemporary Instrumental Analysis(??????), ?????
  
• Gary D. Christian, Analytical Chemistry, 3rd Ed.,
  John Wiley Sons
• Reference
• ????????,????,???????,2001
• ?????????,????? (????????????????????)???????,1994
  ??2?
• ??????????????????????????????,??????
  ???????,1987??1?
• ???????????,????? ?????????,2002.8

3
Chapter 1 Introduction 1. Spectroscopy

• What is spectroscopy?
• A typical spectroscopy experiment is
  extremely simple to describe. Electromagnetic
  radiation at some frequency is allowed to
  interact with the sample of interest. Then some
  property of that radiation is measured, for
  example the amount absorbed, diffracted, emitted,
  scattered, etc. The frequency of radiation to be
  used is determined by the energy levels
  associated with the property of the sample we are
  interested in such as electronic levels,
  rotational motion, vibrational motion, etc.

4

• Spectroscopy includes UV-Vis spectrometry
  (Ultraviolet/visible Absorption Spectrometry), IR
  spectrometry (Infrared Spectrometry), NMR
  (Nuclear Magnetic Resonance Spectroscopy) and MS
  (Mass Spectrometry)
• Rapid and precise analytical methods for organic
  compounds
• Only applied for pure compound
• Hyphenated techniques (GC-MS, GC-IR, LC-MS,
  LC-NMR etc.) for mixture analysis

5
2. Electromagnetic spectrum

• The wave is described with wavelength and
  frequency
• Electromagnetic radiation possess a certain
  amount of energy. The energy of one unit of the
  radiation, the photon, is related to the
  frequency by
• E hv
• E is the energy of the photon in ergs, h is
  Plancks constant, 6.62 x 10-27 erg sec

6
The electromagnetic spectrum

• The electromagnetic spectrum is very wide and
  covers radiation from gamma-rays to visible light
  to radiofrequency waves.
• The visible region is that narrow region of the
  electromagnetic spectrum to which the color
  sensors in our eyes are sensitive. This region,
  which covers wavelengths of 300 nm to 800 nm, has
  energies which are just below the carbon-carbon
  bond strength.

7
(No Transcript)
8
g-rays

• g-rays are also known to cause tissue damage.
  These are very high energy electromagnetic waves
  and are often generated during decay of
  radioactive materials. Usually some dense
  material like lead is necessary to keep them
  contained. Aside from their use in radioactive
  labelling experiments, they are also used in
  Mossbauer spectroscopy which is used to
  investigate nuclear structure. The fact the
  g-rays can destroy a nuclei also make them useful
  for probing properties of nuclei.

9
X-rays

• X-rays can cause damage to tissue and usually
  interact with living matter by breaking bonds.
  The energies associated with x-rays are
  definitely above the bond energies. This is why
  they are used in the treatment of localized
  tumors and they are also known to increase the
  risk of cancer as well. X-rays are used to study
  biological molecules through several processes
  such as scattering and diffraction. Biophysical
  applications of x-rays are concerned mostly with
  the diffraction experiment where detailed
  information about biopolymer structure can be
  obtained. X-rays can be used for this mainly
  because its wavelength (typically used are the Ka
  band of Cu, 1.54A, or Mo, 0.71A) is on the order
  of the length of a chemical bond. We often talk
  of the type of X-rays used in wavelengths on the
  angstrom level or in terms of their energies.

10
Ultraviolet radiation  

• invisible electromagnetic radiation between
  visible violet light and X rays it ranges in
  wavelength from about 400 to 4 nanometers and in
  frequency from about 10 15 to 10 17 hertz. It is
  a component (less than 5) of the sun's radiation
  and is also produced artificially in arc lamps,
  e.g., in the mercury arc lamp.    
•  

11
Visible light 

• The visible region of the electromagnetic
  spectrum consists of photons with wavelengths
  from approximately 400 to 700 nm. The short
  wavelength cutoff is due to absorption by the
  lens of the eye and the long wavelength cutoff is
  due to the decrease in sensitivity of the
  photoreceptors in the retina for longer
  wavelengths. Light at wavelengths longer than 700
  nm can be seen if the light source is intense.

12
(No Transcript)
13
Infrared radiation IR

• If we travel the other direction down the
  electromagnetic spectrum from visible light, we
  discover the infrared region. This region can be
  used to sense heat since it generates heat as a
  by-product of the vibrations it induces. IR is
  used to investigate vibrational modes of
  molecules. It is usually measured in wave
  numbers (cm-1) which is the inverse of the
  wavelength of the IR radiation.

14
Microwaves

• Microwaves can be used to investigate the
  rotational properties of molecules as well as
  electron spin properties. EPR NMR. At these
  frequencies, there is no appreciable spontaneous
  emission and we must rely on the surroundings to
  provide or absorb the energy to attain
  equilibrium. All emissions are now stimulated.
  This applies both to NMR and EPR. Unlike other
  spectroscopies, we can change the sensitivity not
  only by temperature but also by increasing the
  magnetic field used to split the spin energy
  levels. We are allowed to fine tune the
  Boltzmann distribution. This is only one of the
  reasons NMR spectroscopist keep buying more
  powerful magnets.

15
Absorption

• Matter can capture electromagnetic radiation and
  convert the energy of a photon to internal
  energy. This process is called absorption.
• Absorption spectroscopy is one way to study the
  energy levels of the atoms, molecules, and
  solids. An absorption spectrum is the absorption
  of light as a function of wavelength. The
  spectrum of an atom or molecule depends on its
  energy-level structure, making absorption spectra
  useful for identifying compounds.

16
Adsorption Spectrum