Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.
Upcoming SlideShare
UV visible spectroscopy
UV visible spectroscopy
Loading in …3
×
1 of 23

INTRODUCTION TO SPECTROSCOPY

22

Share

Download to read offline

Related Books

Free with a 30 day trial from Scribd

See all

Related Audiobooks

Free with a 30 day trial from Scribd

See all

INTRODUCTION TO SPECTROSCOPY

  1. 1. INTRODUCTION TO SPECTROSCOPY
  2. 2. HISTORY • THE BEAUTIFUL PHENOMENON OF “RAINBOW” WAS THE FIRST DISPERSED SPECTRUM. • 1665 - NEWTON TOOK THE FIRST & MOST IMPORTANT STEP TOWARDS THE DEVELOPMENT OF SPECTROSCOPY. • 1752 - THOMAS MELVILL GAVE THE FIRST DESCRIPTION OF LABORATORY EMISSION SPECTRUM. • 1802 - THOMAS YOUNG SHOWED THAT THE RANGE OF WAVELENGTH IN VISIBLE SPECTRUM EXTENDS FROM 424-675 NM. • FRAUNHOFFER RULED THE FIRST GLASS TRANSMISSION GRATING. • 1848 - FOUCAULT’S WORK INDICATED A RELATION BETWEEN EMISSION & ABSORPTION SPECTRA.
  3. 3. • 1859 - G.R. KIRCHOFF STATED THAT “RATIO OF EMISSIVE POWER TO THE ABSORPTIVITY FOR THERMAL RADIATION IS CONSTANT FOR SAME WAVELENGTH & TEMPERATURE”. • G.R. KIRCHOFF & R.BUNSEN EMERGED AS THE “FATHER OF MODERN SPECTROSCOPY”. • NEW DEVELOPMENTS SUCH AS DRY GELATIN PHOTOGRAPHIC PLATE, INTERFEROMETER,BOLOMETER ETC. CAME IN THE TWENTIETH CENTURY. • INFRARED,MICROWAVE,SUBMILLIMETER,RADIO- FREQUENCY,U.V.,X-RAY,GAMMA –RAY REGIONS CAME INTO EXISTENCE WITH THE HELP OF SPETROSCOPY. • SPECTROSCOPY PLAYED A GREAT ROLE IN THE FORMULA- TION OF QUANTUM MECHANICS & RELATIVISTIC THEORY IN THE TWENTIETH CENTURY.
  4. 4. SINCE,WE ALL ARE FAMILIAR WITH “MATTER” AND THE “ELECTROMAGNETIC RADIATION”. SO,WITHOUT WASTING MUCH TIME, IT IS DEFINED AS THE STUDY OF THE INTERACTION OF MATTER & ELECTROMAGNETIC RADIATION.
  5. 5. …. REVIEW OF SOME BASICS • c= x • Angular resolution: = 1.22 / D radians 206,265” in a radian • E=h • F = L / 4 d2 • Important constants : G = 6.67 x 10-8 (c.g.s) c = 3 x 1010 cm/sec, k = 1.38 x 10-16 h = 6.626 x 10-27 mH ~ mproton = 1.67 x 10-24 grams me = 0.91 x 10-27 grams eV = 1.602 x 10-12 erg Luminosity of Sun = 4 x 1033 erg/sec Mass of the Sun = 2 x 1033 grams
  6. 6. THE PHYSICS OF EM RADIATION • Light: - = c = 2.998 x 1010 cm/s (in vacuum) - E=h Photon energy (erg) 1 erg sec-1 = 10-7 Watt h = 6.626 x 10-27 (c.g.s) 1 eV = 1.602 x 10-12 erg - p =E/c=h/ Photon momentum - = h / p = h / m v de Broglie wavelength Planck Function: B (T) • Emission, absorption, continua • Wave no. : Reciprocal of wavelength (in cm)
  7. 7. •SPECTROSCOPY : STUDY OF INTERACTION OF MATTER AND ELECTROMAGNETIC RADIATION. • SPECTROMETRY : AN ANALYTICAL TECHNIQUE IN WHICH EMISSION (OF PARTICLE/RADIATION) IS DISPERSED ACCORDING TO SOME PROPERTY OF THE EMISSION AND THE AMOUNT OF DISPERSION IS MEASURED. EG. MASS SPECTROMETRY. • SPECTROPHOTOMETRY : A QUANTIFIABLE STUDY OF ELECTROMAGNETIC SPECTRA. • SPECTROGRAPHY : ANOTHER NAME FOR SPECTROSCOPY.
  8. 8. TYPES OF SPECTROSCOPY • Electromagnetic Waves: Emission, absorption Visual, near-IR., FIR, Radio, UV/X-ray, gamma-ray - Solids, liquids, gasses, plasmas - Emission, absorption - Spectral line, molecular bands, continua: - Thermal (~LTE, blackbody, grey-body): - Non-thermal (masers, synchrotron, …) - Electronic, vibrational, rotational transitions. - Effects of B (Zeeman), E ( Stark), motion (Doppler), pressure (collisions), natural life-time (line widths) - Radiative Transfer (optical depth) Other types (not covered in this course): • NMR • Raman • Phosprescence / Fluorecence • Astro-particle
  9. 9. CONTINUOUS SPECTRA ARISE FROM DENSE GASESOF THE DISCRETE SPECTRA ARE THE OBSERVABLE RESULT OR SOLID OBJECTS WHICH RADIATE THEIR HEAT AWAY PHYSICS OF ATOMS. THROUGH THE PRODUCTION OF LIGHT. SUCH OBJECTS EMIT LIGHTTWO TYPES OF DISCRETE SPECTRA : THERE ARE OVER A BROAD RANGE OF WAVELENGTHS, THUS THE APPARENT SPECTRUM SEEMS SMOOTH AND CONTINUOUS. • EMISSION (BRIGHT LINE SPECTRA) , • ABSORPTION EMIT LIGHT IN A PREDOMINANTLY (BUT NOT STARS (DARK LINE SPECTRA) . COMPLETELY!) CONTINUOUS SPECTRUM.
  10. 10. WHEN AN ATOM DROPS FROM EXCITEDENERGY LEVEL TO MOVES FROM LOWER STATE TO THE UPPER ENERGY THEY , THE WAVELENGTHS GROUND STATE,LEVEL EMIT A WAVE OF LIGHT OF CORRESPONDING TO TO THE ENERGY DIFFERENCE WAVELENGTH EQUALPOSSIBLE ENERGY TRANSITIONS WITHIN THAT ATOM WILL BE ABSORBED AND BETWEEN THOSE TWO LEVELS. THIS ENERGYTHEREFORE AN OBSERVER WILL NOT SEE THEM. IN THIS WAY, A “DARK- CORRESPONDS TO A CERTAIN COLOUR, AND THUS WE ARE LINE TO SEE AN “EMISSION SPECTRA”. THE CHANGE OF ABLEABSORPTION SPECTRUM” IS BORN. EG. ENERGY IN AN ATOM GENERATES A PHOTON,WHICH IS THEN EMITTED. EG. A hydrogen atom in the ground state is excited by a photon of exactly the `right' energy needed to send it to level 2, absorbing the level 1, in the process. An excited Hydrogen atom relaxes from level 2 to photon yielding a photon. This results in a dark absorption line. bright emission line.
  11. 11. ABSORPTION SPECTROSCOPY • DEFINITION : ABSORPTION SPECTROSCOPY REFERS TO SPECTROSCOPIC TECHNIQUES THAT MEASURE THE ABSORPTION OF RADIATION, AS A FUNCTION OF FREQUENCY OR WAVELENGTH, DUE TO ITS INTERACTION WITH A SAMPLE. • THE INTENSITY OF THE ABSORPTION VARIES AS A FUNCTION OF FREQUENCY, AND THIS VARIATION IS THE “ABSORPTION SPECTRUM”. ABSORPTION SPECTROSCOPY IS PERFORMED ACROSS THE “ELECTROMAGNETIC SPECTRUM”.
  12. 12. ATOMIC ABSORPTION SPECTROSCOPY • DEFINITION : ATOMIC ABSORPTION SPECTROSCOPY IS A TECHNIQUE USED TO DETERMINE THE CONCENTRATION OF A SPECIFIC METAL ELEMENT IN A SAMPLE. • THE TECHNIQUE CAN BE USED TO ANALYZE THE CONCENTRATION OF OVER 70 DIFFERENT METALS IN A SOLUTION. • PRINCIPLE : IT MAKES USE OF ABSORPTION SPECTROMETRY & IS HENCE, BASED ON “BEER-LAMBART’S LAW”. • INSTRUMENT : Atomic Absorption Spectrometer
  13. 13. ATOMIC EMISSION SPECTROSCOPY • DEFINITION : IT IS THE QUANTITATIVE MEASUREMENT OF THE OPTICAL RADIATION FROM EXCITED ATOMS, WHEN THEY FALL TO GROUND STATE, TO DETERMINE ANALYTE CONCENTRATION. • THIS TECHNIQUE MAKES USE OF HIGH TEMPERATURE OF FLAME TO EXCITE THE ATOMS. • INSTRUMENT : Inductively-coupled Plasma Atomic Emission Spectrometer
  14. 14. ATOMIC EMISSION SPECTROMETER Excited Wavelength electrons selector Excitation source Detector
  15. 15. FLAME PHOTOMETRY • DEFINITION : FLAME PHOTOMETRY (MORE ACCURATELY CALLED FLAME • THE INTENSITY OF THE LIGHT EMITTED COULD BE DESCRIBED BY THE ATOMIC EMISSION SPECTROMETRY) IS A BRANCH OF ATOMIC SPECTROSCOPY “SCHEIBE-LOMAKIN EQUATION”: IN WHICH THE SPECIES EXAMINED IN THE SPECTROMETER ARE IN THE FORM OF I=K×CN ATOMS. THE ATOMS UNDER INVESTIGATION ARE EXCITED BY LIGHT. WHERE, C : CONCENTRATION OF ELEMENT, • THE TECHNIQUE CAN BE USED FOR QUALITATIVE AND QUANTITATIVE K : PROPORTIONALITY CONSTANT, DETERMINATION OF SEVERAL CATIONS, ESPECIALLY FOR METALS THAT ARE N : N ~1 (AT LINEAR PART OF CALIBRATION CURVE) EASILY EXCITED TO HIGHER ENERGY LEVELS AT A RELATIVELY LOW FLAME THEREFORE ,THE INTENSITY OF TEMPERATURE (MAINLY NA, K, RB, CS, CA, BA, CU). EMITTED LIGHT IS DIRECTLY PROPORTIONAL TO CONCENTRATION. • PRINCIPLE : IT MAKES USE OF A FLAME THAT EVAPORATES THE SOLVENT AND ALSO SUBLIMATES AND ATOMIZES THE METAL AND THEN EXCITES A VALENCE • INSTRUMENT : ELECTRON TO AN UPPER ENERGY STATE. Photograph of a flame photometer
  16. 16. FLAME PHOTOMETER Readout Aerosol enters flame Photo-detector Fuel Lens Filter Air Discharge
  17. 17. U.V., I.R., VIS. SPECTROPHOTOMETRY • U.V. SPECTROPHOTOMETRY : IT IS A BRANCH OF A.A.S/A.E.S IN WHICH ALL ATOMS ABSORB/EMIT WAVELENGTH OF LIGHT CORRESPONDING TO U.V. REGION . IT IS USED IN QUANTIFYING PROTEIN AND DNA CONCENTRATION AS WELL AS THE RATIO OF PROTEIN TO DNA CONCENTRATION IN A SOLUTION . • I.R. SPECTROPHOTOMETRY : IT IS ALSO A BRANCH OF A.A.S/A.E.S IN WHICH ALL ATOMS ABSORB/EMIT WAVELENGTH OF LIGHT CORRESPONDING TO I.R. REGION. INFRARED SPECTROSCOPY OFFERS THE POSSIBILITY TO MEASURE DIFFERENT TYPES OF INTER ATOMIC BOND VIBRATIONS AT DIFFERENT FREQUENCIES . • VIS. SPECTROPHOTOMETRY : IT IS THE THIRD BRANCH OF A.A.S/A.E.S IN WHICH ALL ATOMS ABSORB/EMIT WAVELENGTH OF LIGHT CORRESPONDING TO VISIBLE REGION.
  18. 18. SPECTROPHOTOMETER
  19. 19. FLUORIMETRY • DEFINITION : IT IS A TECHNIQUE IN WHICH THE AMOUNT OF SUBSTANCE IN A SAMPL CAN BE DETERMINED BY THE AMOUNT OF LIGHT EMITTED BY THE ATOMS OF THAT SUBSTANCE. • THIS TECHNIQUE IS BASED ON THE PHENOMENON OF “FLUOROSCENCE”. • RELATION BETWEEN FLUOROSCENCE INTENSITY & ANALYTE CONCENTRATION : F= K*(QE)*(Po)*[ 1- 10(A*B*C)]
  20. 20. SPECTROGRAPH Focal Plane collimator camera detector Dispersing element Slit Telescope
  21. 21. SPECTROGRAPH OVERVIEW • Slit & Decker: Restrict incoming light Spatial direction vs. Spectral direction • Collimator & Camera: Transfer image of slit onto detector. • Grating: Disperse light: dispersion => spectral resolution • What determines spectral resolution & coverage? - Slit-width - Grating properties: Ngrooves , order number - Camera / collimator magnification (focal length ratio) - Detector pixel size and number of pixels.

×