Presentation on theme: "INTRODUCTION TO SPECTROSCOPY G. RAM KUMAR BY Department of Chemistry"— Presentation transcript:
1 INTRODUCTION TO SPECTROSCOPY G. RAM KUMAR BY Department of Chemistry Pydah College P.G. Courses
2 INTRODUCTION TO SPECTROSCOPY It is the most powerful tool available for the study of atomic and molecular structures.It is used in the analysis of wide range of samples.What is spectroscopy?Spectroscopy may be defined as the study of interactions between the matter and Electro Magnetic Radiations.
3 TYPES OF SPECTROSCOPYAtomic Spectroscopy : It is concerned with interactions of Electro Magnetic Radiations with atoms.Molecular Spectroscopy : It is concerned with interactions ofElectro Magnetic Radiations with molecules .In general all the Spectroscopic methods are classified into two.Non-Destructive methods Ex:UV-Visible , IR , NMR.Destructive methods Ex:FES , AAS , ICP-MS.
4 ELECTROMAGNETIC RADIAIONS Electromagnetic radiation is an oscillating electric and magnetic disturbance that spreads as a wave through empty space, the vacuum
5 Wave length(λ): It is the distance between two crests or troughs. CHARACTERISTICS OF ELECTROMAGNETIC RADIATIONSWave length(λ): It is the distance between two crests or troughs.Units: Å Angstroms or Nanometers nm1 Å=10-8cm=10-10m1nm=10 Å=10-9cmFrequency(υ): It is defined as the number of waves which can pass through a point in one second.Units: Hertz(Hz); Fresnel1Hz = 1cycle/sec; 1Fresnel = Hz
6 Wave Number(ΰ): It is the reciprocal of wave length and is defined as the total number of waves which can pass through a space of 1cm.Units: cm-1 or m-11cm-1 is sometimes called 1KAYSER(K)Velocity(v): It is the distance travelled by a wave in 1sec.Units: cm/sec or m/sec
7 DISPERSION OF LIGHTWhen visible light (White light) is passed through prism, it split up into seven colors which corresponds to definite wave lengths.This is known as dispersion of light
10 SPECTRUM:The series of color bands obtained by dispersion of light is known as spectrum.In a spectrum all these bands are arranged in the increasing order of wave length
11 CLASSIFICATION OF SPECTRA: I 1.LINE SPECTRA : Spectrum obtained by interaction of electromagnetic radiations with atoms. Line spectra consists of sharp well defined lines that correspond to a definite frequency2.BAND SPECTRA: Spectrum obtained by interaction of electromagnetic radiations with molecules.Band spectra consists of different bands just as visible spectrum.
12 IICONTINUOUS SPECTRUM:In a spectrum, if one color merges into another without a gap, then the spectrum is known as Continuous spectrum.DISCONTINUOUS SPECTRUM:In a spectrum , if one color will not merge into other is known as Discontinuous spectrum.
13 IIIABSORPTION SPECTRUM:If the electromagnetic radiations are passed through a substance, the dark pattern of lines that are obtained corresponding to wave lengths absorbed is known as Absorption spectrum .EMISSION SPECTRUM:If electromagnetic radiations are passed through a substance, the pattern of lines recorded after the emission of the absorbed wave lengths are known as emission spectrum.
14 ELECTROMAGNETIC SPECTRUM The arrangement of electromagnetic waves or radiations in the order of their increasing wave lengths or decreasing frequencies is called electromagnetic spectrum.
16 Interactions of Different types of Electromagnetic Radiations produce different types of SpectroscopyRegions of EM spectrumRadio frequency regionMicrowave regionInfrared regionUV & Visible regionType of sepctroscopyNuclear magnetic resonance or electron spin resonanceRotational spectroscopyVibrational spectroscopyElectronic spectroscopy
17 Electronic Excitation by UV/Vis Spectroscopy : UV: valanceelectronic excitationRadio waves:Nuclear spin states(in a magnetic field)IR: molecular vibrationsX-ray:core electronexcitation
18 A=ebc The concentration dependence follows Beer’s Law. The wavelength and amount of light that a compound absorbs depends on its molecular structure and the concentration of the compound used.The concentration dependence follows Beer’s Law.A=ebcWhere A is absorbance (no units, since A = log10 P0 / P )e is the molar absorbtivity with units of L mol-1 cm-1b is the path length of the sample - that is, the path length of the cuvette in which the sample is contained (typically in cm).c is the concentration of the compound in solution, expressed in mol L-1
19 } = hv Molecules have quantized energy levels: ex. electronic energy levels.hv}energyenergy= hvQ: Where do these quantized energy levels come from?A: The electronic configurations of associated with bonding.Each electronic energy level (configuration) has associated with it the many vibrational energy levels we examined with IR.
20 max = 135 nm (a high energy transition) Absorptions having max < 200 nm are difficult to observe because everything (including quartz glass and air) absorbs in this spectral region.
22 The n to pi* transition is at even lower wavelengths but is not as strong as pi to pi* transitions. It is said to be “forbidden.”Example:Acetone: n max = 188 nm ; = 1860n max = 279 nm ; = 15