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INFRARED SPECTROSCOPY

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Presentation on theme: "INFRARED SPECTROSCOPY"— Presentation transcript:

1 INFRARED SPECTROSCOPY
Muhammad Yasir Siddique Department of Chemistry University of Gujrat

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3 Introduction Spectroscopy: spectroscopy is the study of interaction of light with matter. OR The study of the interaction between radiations and matter as a function of wavelength λ. Spectrometry: It is the measurement of these responses and an instrument which performs such measurements is a spectrometer or spectrograph, although these terms are more limited in use to the original field of optics from which the concept sprang.

4 Classification of Methods
The type of spectroscopy depends on the physical quantity measured. Normally, the quantity that is measured is an intensity, either of energy absorbed or produced. Absorption Spectroscopy: It uses the range of the electromagnetic spectra in which a substance absorbs. This includes Atomic absorption spectroscopy Infra-red spectroscopy Nuclear Magnetic resonance spectroscopy

5 Classification of Methods
Emission Spectroscopy: It uses the range of electromagnetic spectra in which a substance radiates (emits). The substance first must absorb energy. This techniques include spectroflourimetry. Scattering Spectrometry: It measures the amount of light that a substance scatters at certain wavelengths, incident angles, and polarization angles. One of the most useful applications of light scattering spectroscopy is Raman Spectroscopy.

6 Common types Fluorescence spectroscopy
X-ray spectroscopy and crystallography Flame spectroscopy 1- Atomic emission spectroscopy 2- Atomic absorption spectroscopy 3- Atomic fluorescence spectroscopy Plasma emission spectroscopy Spark or arc emission spectroscopy

7 Common types UV/VIS spectroscopy IR spectroscopy Raman spectroscopy
NMR spectroscopy Photo thermal spectroscopy Thermal infra-red spectroscopy Mass Spectroscopy

8 What is Infrared Spectroscopy?
Is the spectroscopy that deals with the infrared region of the electromagnetic spectrum, that is light with a longer wavelength and lower frequency than visible light.

9 Cont. It is a method of measurement of the extent, at a various wave numbers, of absorption of infrared radiation when it passes through a layer of substances. Infrared Spectrometer determines the wavelength and absorbance of a sample in the infrared region of the electromagnetic spectrum.

10 INFRARED SPECTROSCOPY
Infrared radiation stimulates molecular vibrations. Infrared spectra are traditionally displayed as %T (concentration transmittance) versus wave number ( cm-1). Useful in identifying presence or absence of functional groups.

11 Infrared Spectrometer

12 Infrared Instrumentation
IR Spectrometer Sample compartment Detector IR Source

13 IR Frequency Range The infrared spectrum is divided into three portions, near, mid, and far infrared, covering wave numbers (related to frequency) from 10-14,000 cm⁻¹. The range cm⁻¹ is used for basic laboratory work.

14 Instrumentation Two types of IR spectrometer used commonly in organic lab Dispersive IR Spectrometer Fourier transform(FTIR) Spectrometer Both provides the spectra of compounds in the common rang 4000 t0 400cm-1. FTIR spectrometer provides the infrared spectrum more rapidly than Dispersive Spectrometer.

15 Instrumentation Dispersive IR Spectrometer: Used monochromatic light
%transmittance because detector records the ratio of intensities of two light beam %T=Is/Ir

16 Instrumentation A systematic Diagram of dispersive IR Spectrometer.

17 Fourier transform(FTIR) Spectrometer
The most modern Spectrometer. Produce a pattern called Interferogram(a signal) time vs. intensities. Acquire interferogram less than a second. More Sensitive, More Rapid

18 Fourier transform(FTIR) Spectrometer
A systematic diagram of FTIR.

19 About Sample Sample compartment:
liquid sample :Liquid samples are usually contained in sample cells which are placed in sample cell holders. Cell holders may be heated or cooled in order to control the temperature of the liquid in the sample cell. Gaseous sample: Gases and vapours are measured is similar to those used for liquids. Generally the cell path length is much greater. Gases at any pressure are contained in closed cells for measurement.

20 About Sample Solid samples: Solid samples are held in solid-sample holders. When solid samples are measured, difficulties may be experienced e.g. in matching the sample and reference path lengths. Special samples: Low temperature cells are required for certain applications. These may include cooled cells, thermally insulated cells, and cold-finger cells.

21 Instrumentation Components of IR is Spectrometers: Source
An inert solid is electrically heated range K. The heated material will then emit infra red radiation. The Nernst glower is a cylinder of rare earth oxides. The Nernst glower can reach temperatures of 2200 K. The Globar source is a silicon carbide rod which is electrically heated to about 1500 K.

22 Instrumentation The incandescent wire source is a tightly wound coil of nichrome wire, electrically heated to 1100 K. It produces a lower intensity of radiation than the Nernst or Globar sources, but has a longer working life.

23 Instrumentation Detectors: There are three categories of detectors.
Thermal Pyro electric Photo conducting

24 Cont. Thermocouples consist of a pair of junctions of different metals; for example, two pieces of bismuth fused to either end of a piece of antimony. Pyro electric detectors are made from a single crystalline wafer of a pyro electric material, such as triglyceride sulphate. They are used in most Fourier transform IR instruments. .

25 Cont. Photoelectric detectors such as the mercury cadmium telluride detector. These detectors have better response characteristics than pyro electric detectors and are used in FT-IR instruments - particularly in GC - FT-IR.

26 Instrumentation Detectors
Use either a photomultiplier tube or a diode array. Two major classes of instruments: Photometer(simple instruments, detect single wavelength at a time and inexpensive having good S/N) Spectrophotometer( complex optics scan various wavelength at a time more expensive and lower S/N)

27 Infrared Experimental
Sample Containers: To obtain an IR spectrum, the sample must be placed in a “container” or cell that is transparent in the IR region of the spectrum. Sodium chloride or salt plates are a common means of placing the sample in the light beam of the instrument.

28 Infrared Experimental
IR transparent Salt Plates

29 Infrared Experimental
These plates are made of salt and must be stored in a water free environment such as the desiccator shown here.

30 Infrared Experimental
The plates must also be handled with gloves to avoid contact of the plate with moisture from one’s hands.

31 Infrared Experimental
To run an IR spectrum of a liquid sample, a drop or two of the liquid sample is applied to a salt plate. A second salt plate is placed on top of the first one such that the liquid forms a thin film “sandwiched” between the two plates.

32 Infrared Experimental
The cell holder is then placed in the beam of the instrument. The sample is then scanned by the instrument utilizing predestinated parameters.

33 Infrared Experimental
The salt plates are cleaned by rinsing into a waste container with a suitable organic solvent-commonly cyclohexane - NEVER WATER! Cloudy plates must be polished to return them to a transparent condition.

34 Cloudy plates must be polished to return them to a transparent condition.
To polish cloudy windows, rotate salt plate on polishing cloth.

35 The clean plates and cell holder are stored in the moisture free atmosphere of a desiccator.

36 INFRARED SPECTROSCOPY
What is a vibration in a molecule? Any change in shape of the molecule- stretching of bonds, bending of bonds, or internal rotation around single bonds What vibrations change the dipole moment of a molecule? Asymmetrical stretching/bending and internal rotation change the dipole moment of a molecule. Asymmetrical stretching/bending are IR active. Symmetrical stretching/bending does not. Not IR active

37 INFRARED SPECTROSCOPY
In the IR region of the electromagnetic spectrum, the absorption of radiation by a sample is due to changes in the vibrational energy states of a molecule.

38 Absorption process The pattern of absorption as a function of wavelength is called an IR spectrum.

39 Number of vibrational modes
A molecule can vibrate in many ways, and each way is called a vibrational mode. For molecules with N atoms in them, linear molecules have 3N – 5 degrees of vibrational modes, whereas nonlinear molecules have 3N – 6 degrees of vibrational modes (also called vibrational degrees of freedom). The atoms in a CH2X2 group=> can vibrate in nine different ways.

40 Cont.  Six of these involve only the CH2 portion: symmetric and antisymmetric stretching, scissoring, rocking, wagging and twisting, because CH2 is attached to X2 it has 6 modes, unlike H2O, which only has 3 modes. The rocking, wagging, and twisting modes do not exist for H2O, since they are rigid body translations and no relative displacements exist.)

41 INFRARED SPECTROSCOPY
Methane Rocking or in plane bending H C Asymmetrical stretching Symmetrical stretching Bending or scissoring Twisting or out-of-plane bending Wagging or out-of-plane bending

42 INFRARED SPECTROSCOPY
Only vibrations that cause a change in ‘polarity’ give rise to bands in IR spectra – which of the vibrations for CO2 are infrared active? Symmetric stretch Asymmetric stretch Bending (doubly degenerate)

43 Uses and Applications Detection of functional groups
Detection of impurities(compound is pure or not) Detection of conc. of acids &bases at diff.PH Infrared spectroscopy is a simple and reliable technique widely used in both organic and inorganic chemistry, in research and industry. It is used in quality control, dynamic measurement, and monitoring applications such as the long-term unattended measurement of CO2 concentrations in greenhouses and growth chambers by infrared gas analyzers.

44 Uses and Applications It is also used in forensic analysis in both criminal and civil cases, for example in identifying polymer degradation. Chemical Analysis: Testing Pill Quality. According to "Medical News Today," scientists at the University of Maryland have been successful in using the method of near-infrared spectroscopy (NIR) to make a prediction regarding quick dissolution of pills inside the body. The success of the experiment can help drug manufacturers in checking the quality of pills to benefit consumers in the health industry.

45 Cont. Chemistry Applications. Using infrared spectroscopy, it is possible to measure the degree of polymerization in chemical compounds. Polymerization happens when monomer molecules undergo chemical reaction to form polymer chains. Infrared spectroscopy can measure the changes in the nature and quantity of molecular bonds. Portable instruments that can measure infrared spectroscopy are used in field trials. This method is important for researchers in identifying more uses of different substances to improve the lives of modern society. Medical breakthroughs are not far behind. The analysis of molecular compounds can lead to the discovery of new chemical compounds that can produce useful products.

46 References: [1] (online accessed on 29, Dec 2013) [2] (online accessed on 29, Dec 2013) [3] P. Sherman Hsu, Ph.D. “Infrared Spectroscopy”.- Separation Sciences Research and Product Development Mallinckrodt, Inc. Mallinckrodt Baker Division pp. 252, 1992. DL.Pavia, GM.Lampman, GS.Kriz, Introduction to “Spectroscopy” 3rd edition. (John Vondeling, Sandy Kiselica. Editors) Thomson Learner Publications, Australia, Asia, Canada, America, spain, pp , 2001. Robert M. Silverstein, Francis X. Webster, David J. Kiemle “Spectrometric Identification of Organic Compounds” edition 7th. (John Wiley & Sons publications) pp , 2005.

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48 Thank You And always welcome


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