Molecular Spectroscopy For UG and PG Part 1.pptx

General Molecular Spectroscopy for UG and PG Students. Part-I

1. Shri Shivaji Education Society Amravati’s Shri Shivaji Arts, Commerce & Science College Motala , Dist. Buldana

2. Molecular Spectroscopy Part-1 By Mr. Bhaskarrao Subhashrao Bhise Assistant Professor Shri Shivaji Arts, Commerce & Science College Motala Dist. Buldana

3. CONTENT 1 2 3 4 5 Introduction Elecromagnetic Radiation Electromagnetic Spectrum Types of Spectra Degree of Freedom

4. Introduction:- Spectroscopy is a branch of Chemistry which deals with the study of interaction of electromagnetic radiation with matter ( Atom or Molecule). It is most powerful technique for understanding of atomic structure and structure of molecule. Electromagnetic Radiation:- Electromagnetic radiation is a form of energy that transmitted through space with velopcity of light ( C=3x10 8 ms -1 ). Electromagnetic radiation combine with electric and magnetic field which are perpendicular to each other and also perpendicular to direction of propagation. Electromagnetic radiation ( EMR ) consider as simple harmonic wave propogated in space, in straigth line. EMR spread over range of wavelength. i.e. Visible light, IR radiation, X-ray, ɤ-ray, Microwave and radiowave are the example of electromagnetic radiation. EMR exibit dual in nature ( wave as well as particle) Characteristic of Electromagnetic Radiation:- 1. All EMR associated with oscillating electrical and magnetic vectorat right angle to each other and also right angle to direction of propagation.

5. 2 . All EMR have same speed in vacuum. They travels in vacuum with speed of light. 3. Energy can be transmitted through space by EMR. Different types of EMR they differ from their wavelength. Velocity of all EMR is constant, greater the frequency of radiation smaller its wavelength. EMR characterized by wavelength, wave number, frequency, time period, amplitude wave and velocity.

6. Parameters of EMR Wavelength:- It is defined as the distance between two successive crests (maxima) or troughs (minima) in EMR. IT is denoted by Greek letter Lambada (𝜆) It is measure in unit of nm(nanometer), mm(millimeter), μ m(micrometer), cm(centimeter) or m(meter) and A . 1nm=10 -9 m, 1 μ m=10 -6 m, 1mm=10 -3 m 1cm=10-2m, 1A =10 -8 cm, 1A =10 -10 m. 2. Frequency:- The number of waves passing through a given point in unit time called as frequency. It is denoted by Greek letter υ and unit has reciprocal time.. Generally expressed in cycles per second or in Heartz . 1Hz= 1 cycle/sec=S-1; υ =C/𝜆

7. 3. Wave number:- It is defined as no. of waves per unit length. It is denoted by ⩢ and expered in cm- 1 ⩢= 1/𝜆 = 1/ wavelength 4. Velocity:- The distance traveled by wave in one second is called as velocity. It is denoted by c and expressed in centimeter per second (cm/s) or meter per second (m/s). c= v𝜆 5. Energy:- The energy (E) assiciate with quantum of electromagnrtic radiation is given by E= hv =   Where, h= planks constant (h=6.62 10 -34 JS), V= Frequency (Hz), 𝜆=wavelength (m). C= velocity of light (C=3 10 8 m/s)  

8. Spectrum of Electromagnetic Radiation :- The entire range of wavelength over which EMR occur known as EMR. Various range of spectrum of EMR given below.

9. Characteristics of spectral regions -Ray :- The wavelength between 1pm to 100pm ( 0.001-0.1nm). The gamma ray shortest waves emitted by atomic nuclei. Ray :- The wavelength range between 100pm to 10nm. X-Rays emitted or absorbed by movement of electron close to the nuclei. The wavelength in this region lies between 10 nm to 400 nm. Electronic transition obtained by absorption of UV-light. 4 The wavelength region between 400-800 nm. Visible light also produce electronic transition. 5 The wavelength range between about 0.8 μ m to 100 μ m. IR radiation induce vibrational transition in molecules. The region divided following sub-region Near IR → 0.8 to 2.5 μ m Mid IR → 2.5 to 15 μ m, Far IR → 15 to 100 μ m   -Ray :- The wavelength between 1pm to 100pm ( 0.001-0.1nm). The gamma ray shortest waves emitted by atomic nuclei. Ray :- The wavelength range between 100pm to 10nm. X-Rays emitted or absorbed by movement of electron close to the nuclei. The wavelength in this region lies between 10 nm to 400 nm. Electronic transition obtained by absorption of UV-light. 4 The wavelength region between 400-800 nm. Visible light also produce electronic transition. 5 The wavelength range between about 0.8 μ m to 100 μ m. IR radiation induce vibrational transition in molecules. The region divided following sub-region Near IR → 0.8 to 2.5 μ m Mid IR → 2.5 to 15 μ m, Far IR → 15 to 100 μ m  

10. 6. Microwave Region:- The wavelength between 100 μ m to 1cm (0.1 mm to 1cm). This region correspond to rotational transition in molecules. 7. Radio Rrequency Region:- The wavelength region between 1cm to 10m. Radio waves are useful in N.M.R. and E.S.R. spectroscopy. Types of Spectra Spectrum: When a beam of light is passed through a prism or gratin , it split up into its constituent colour . This array of colors called as spectrum. Absorption Spectra Continuous Discontinuous Spectra Discontinuous Continuous Line-Spectra Band Spectra Line-Spectra Band Spectra Emission Types

11. Emission Spectrum:- This spectrum obtained when light coming after passing through a prisn or grating, is examined directly with spectroscope. Emission spectrum classified as continuous, line and band spectrum. a) Continuous spectrum:- This type spectrum obtained from bulk matter heated, by emit radiation continuously. Ex. Hot filament, hot iron, hot charcoal give continuous spectrum. b) Line spectrum:- This is obtained when light emits in the atomic state, called as atomic spectrum. Ex. Light source like Mercury, Sodium, Neon discharged tube etc. c) Band Spectrum:- This type spectrum obtained when emitted in the molecular state is excited. Emitted light band is observed under high resolution power. It is observed that band contains large number of lines. 2. Absorption Spectrum: 2. Absorption Spectrum:- When light continuous absorbed from source of light and it is observed through spectroscope. It is observed that certain colours are missing which leave dark line/spot/band places, the observed spectrum called as absorption spectrum. There are three types of absorption spectrum.

12. Continuous Absorption Spectrum:- This type spectrum arises when absorbing material absorb continuous of wavelength. Ex. Red glass absorb all colour except red colour. Line absorption Spectrum:- This type of sharp line observed by absorption in vapour or gases phase. Ex. The spectrum obtained from sun gives absorption lines corresponding to vapour of different element. c) Band Absorption Spectrum:- Absorption of spectrum in the form of dark bands, known as band absorption spectrum. Ex. Aqueous solution of KMnO4 gives five absorption band in the green region. 3. Atomic Spectra:- These spectra consist of definite wavelength and given by gases and vapour of atoms.also called as atomic spectra. 4. Molecular Spectra:- When molecule absorb radiation it get excited and when it returns to ground state, it emits band which characteristics of molecule concerned called as molecular spectra. Molecule absorb light energy then, three types of transition energy take places.

13. a) Rotational Transition Energy:- When molecules absorb nearly equal to 0.005 ev , we get rotational transition from one rotational energy to another rotational energy level. Rotatioanl energy of simple molecules given by J(J+1) Where, J=Rotational quantum number h=planks constant, I= Moment of inertia.   b) Vibrational Transition Energy:- When molecule absorb energy equal to 0.1 ev , to produce rotational transition. The energy involve for this transition called as rotational transition energy. Vibration of molecules inside the molecules. Rotational transition along with vibrational transition called as vibrational rotational spectra.

14. The vibrational energy given by E vib =( V + ½) hv V=Vibrational quantum number. c) Electronic Transition Energy:- When molecule absorb energy nearly equal to 50 to 100 ev , then there is transition of electron from lower energy to higher energy level are called as electronic transition. Energy involved for these transition called electronic transition energy and spectra called as electronic spectra. In electronic transition also occur rotational and vibrational transition.

15. Degree of Freedom Degree of freedom is use for which transition present in the molecules . The degree of freedom in polyatomic molecules is the sum of coordinates necessary to locate all the atom of molecules. Each atom has three degree of rotation correspond to to three axis ( X, Y & Z). A molecule will thus be made of rotational, vibrational and transitional degree of freedom. Thus, 3n degree of freedom = Transitional + Rotational + Vibrational. The rotational degree of freedom results from rotational of molecule about an axis through the center of gravity. Ex. Liner molecule. This molecule rotate about all three axis but rotation about internuclear axis will not produce any change in the position of atom. Thus, linear molecule has two rotational degree of freedom and non linear molecule has three rotational degree of freedom.

16. For Linear Molecule For Non-Liner molecule Total degree of freedom = 3n Transitional degree of freedom =3 Rotational degree of freedom = 2 Vibrational degree of freedom = 3n-5 Example 1Diatomic HCl n=3 ( Two atom) Total degree of freedom = 3n =3x2 =6 Transitional degree of freedom =3 Rotational degree of freedom = 2 Vibrational degree of freedom = 3n-5=6-5=1 Total degree of freedom = 3n Transitional degree of freedom =3 Rotational degree of freedom = 3 Vibrational degree of freedom = 3n-6 Example 1 Triatomic H 2 O n=3 ( Three atom) Total degree of freedom = 3n =3x3 =9 Transitional degree of freedom =3 Rotational degree of freedom = 3 Vibrational degree of freedom = 3n-6=9-6=3

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