LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M. Sc. DEGREE EXAMINATION – PHYSICS

FIRST SEMESTER – NOVEMBER 2003

PH 1804 / PH 725 – SPECTROSCOPY

11.11.2003                                                                                              Max.   : 100 Marks

1.00 – 4.00

PART – A

 

Answer ALL the questions.                                                                         (10 x 2 = 20)

 

1. How are molecules classified on the basis of moment of inertia? Give one example for each.
2. The moment of inertia of OCS molecule is 137.95 x 10^-47 kg-m². Calculate the rotation constant.
3. What type of spectroscopy is best suited for H₂? Give reasons.
4. Explain with an example, the rule of mutual exclusion.
5. What is Fortrat parabola?
6. The band origin of a transition in C₂ is observed at 19378 cm^-1 while the rotational fine structure indicates that the rotational constants in excited and ground states are respectively B¹ = 1.7527 cm^-1 and B¹¹ = 1.6326 cm^-1. Estimate the position of the band head.
7. Define quadruple moment of a nucleus.
8. Give the importance of double resonance technique.
9. Calculate the magnetic field strength required to get transition frequency of 60 MHz for hydrogen nuclei.
10. A Mossbauer nucleus has spin 1/2 and 3/2 in the ground state and excited state respectively. Sketch the Spectrum when combined electric and magnetic fields are present.

PART – B

 

Answer any FOUR                                                                                     (4 x 7.5 = 30)

 

11. a) Explain the factors that determine the intensity of a spectral line. Obtain an expression for J at which maximum population occurs.

 

20. b) The separation between lines in the rotational spectrum of HCl molecules was found to be 20.92 cm^-1. Calculate the bond length.

 

12. a) How many normal modes of vibration area possible for H₂O? Show by sketch the fundamental vibrational modes of H₂O molecule.

 

1. b) Outline the theory of Raman spectrum on the basis of (1) Classical theory and (2) Quantum theory.

 

13. Explain the importance of Franck-Condon principle in explaining the intensity of molecular Spectrum.
14. Discuss the T₁ and T₂ relaxation mechanism in NMR. Derive an expression for the relaxation time T₁.
15. Explain with a neat diagram, the functioning of Electron energy loss spectrometer.

-2-

PART – C

 

 

Answer any FOUR                                                                                   (4 x 12.5 = 50)

 

16. (a) Explain, with theory, the spectrum of a linear diatomic molecule of rigid rotor type. Deduce the correction for non-rigid type.

 

(b) Calculate the frequency of  NO  molecule whose force constant is 1609 Nm^-1.

 

17. (a) Explain Born-Oppenheimer      Describe, with theory,  the rotation – vibration spectra of a diatomic molecule.

 

(b) The fundamental and first overtone transition of   ¹⁴N, ¹⁶O are centered at 1876.06 cm^-1 and 3724.20 cm^-1 respectively. Equivalent the equilibrium frequency, anharmonicity constant and zero point energy.

 

18. Obtain an expression for the Dissociation energy of a molecule. The Vibrational Structure of the absorption Spectrum of O₂ becomes a continuum at 56,876 cm^-1. If the upper electronic state dissociates into one ground state atom and one excited atom with excitation energy 15,875 cm^-1, estimate the dissociation energy of ground state of O₂ in cm^-1 and kJ / mole.

 

19. Explain the principle of ESR. Sketch a neat diagram and explain the functioning of ESR Spectrometer.

 

20. Outline the importance of ‘RAIRS’ technique in characterising the absorbed surfaces on a specimen.

 

 

 

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