LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

THIRD SEMESTER – APRIL 2012

CH 3810 – MOLECULAR SPECTROSCOPY

 

 

Date : 26-04-2012             Dept. No.                                        Max. : 100 Marks

Time : 1:00 – 4:00

 

PART – A

 

Answer all the questions:                                                                                                      (10 x 2 = 20)

 

1. Calculate the reduced mass and moment of inertia of D³⁵Cl using internuclear distance of 0.1275nm.
2. Classify rotators into different kinds based on moment of inertia values.
3. What is the selection rule for Raman vibrational-rotational spectrum?
4. Wavelength of incident radiation is 5460 ^oA and Stokes line appear at 5520^o Calculate the wavelength of anti Stoke line.
5. What is photoelectric effect? How does it help in explaining the principle of PES?
6. Calculate the strength of the magnetic field to get a precessional frequency of 100 MHz for ¹⁷O nucleus. Given: g_n = 0.757.
7. Distinguish between diagonal and off-diagonal peaks in 2D NMR.
8. Account for the ‘zero’ asymmetry parameter observed in the case of axially symmetric molecules.
9. Define: Quadrupole splitting.
10. A free electron is placed in a magnetic field of strength 1.3T. If g_e is 2.0023, and β_e is 9.27×10^-24 JT^-1, find the ESR frequency in GHz.

PART – B

Answer any EIGHT questions:                                                                                                  (8 x 5 = 40)

 

11. Explain the various factors affecting the intensity of spectral lines.
12. Write notes on i) chromophore and auxochrome ii) bathochromic and hypsochromic shift of UV band.
13. Describe Fermi resonance.
14. What is zero point energy? How does it explain the Raman scattering for molecules even when their vibrational quatum number is zero?
15. A microwave spectrometer capable of operating only between 60 and 90 cm^-1 was used to observe rotational spectra of HI and DI.

HI (cm^-1)                     DI (cm^-1)

64.275                         65.070

77.130                         71.577

89.985                         78.094

 

Find B, I, r for each molecule.

 

 

16. How does PES help in computing binding energy of electron in orbitals.
17. How is coupling constant calculated? Mention its significance.
18. Predict the spin-spin splitting patterns for 2,3-dimethyl butane and neopentane.
19. Explain i)zero field splitting ii) anisotropy in g value.
20. NQR spectroscopy lies between NMR and Mossbauer spectroscopy – explain.
21. The compound AB₃ has C₃ axis and its quadrupole resonance yields q_zz a value of 3×10²⁵. Find out its NQR frequency. Given: Q = -0.08×10^-24cm².
22. What is recoilless resonance emission and absorption? How can a Mossbauer nucleus be prevented from recoiling?

PART-C

Answer any FOUR questions:                                                                                            (4 x 10 = 40)

 

23. a) Derive the energy expression for anharmonic vibrator.
24. b) The fundamental, first and second overtones appear for HCl as 2886, 5668 and 8347cm^-1 Calculate w_e and x_e for HCl.
25. How do quantum theory and classical theory explain Ramaneffect?
26. How are IR and Raman spectroscopy helpful in explaining
27. i) SO₂, as symmetric and bentii) CO₂, as linear with center of symmetry

iii) N₂O,linear without center of symmetry.

26. a) Explain i) Diamagnetic anisotropy ii) geminal and vicinal coupling
27. b) How are long range coupling detected in COSY?
28. a)Obtain the energy levels and show the NQR transitions possible in nucleus with spin i) I = 7/2  ii) I = 5/2.
29. b) Sketch the ESR spectrum possible for i) ˙NH₂ radical ii) naphthalene in triplet state.

28.a) Discuss the Mossbauer transitions in ⁵⁷Fe nucleus observed due to i) quadrupole splitting   ii) hyperfine Zeeman splitting.

b)Explain the principle of FAB Mass spectrometry.

 

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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

THIRD SEMESTER – NOVEMBER 2012

CH 3810 – MOLECULAR SPECTROSCOPY

 

 

Date : 06/11/2012            Dept. No.                                        Max. : 100 Marks

Time : 9:00 – 12:00

 

PART A

Answer all the questions:                                                                                                        10×2=20

1. How are absorption and emission spectra formed?
2. Define S/N ratio.
3. Mention the differences between Rayleigh and Raman Scattering.
4. State Frank Condon principle.
5. How many normal modes of vibration are possible for HBr and SO₂(bent) ?
6. Determine the magnetic field strength of an NMR instrument in which a proton chemical shift of 2.2ppm corresponds to a frequency of 1100Hz. Given g_n = 5.585
7. Sketch the ¹H NMR of pure n-propanol.
8. Obtain the ‘g’ value for Mn²⁺
9. Which of the following gives NQR? Chlorine liquid or Chlorine solid. Justify your choice.
10. When can a system exhibit quadrupole splitting?

PART B

Answer any eight questions:                                                                                                  8×5=40

 

11. What are the factors that affect the width of the spectral lines? Explain.
12. Explain the following for the linear and nonlinear polyatomic molecules.
13. a) fundamental vibrations       b) overtones and combination frequencies
14. Briefly explain the principle of diatomic vibrating rotor when DJ = +1 and -1.
15. Discuss the different regions of the electromagnetic radiation.
16. Explain the fingerprint and absorption frequencies of functional groups for organic compounds in IR region?
17. Describe the effect of isotopic substitution in rotational spectra.
18. What are short range and long couplings? Give an example each.
19. Arrive at the structures of H₃PO₃ and H₃PO₂ whose ³¹P NMR show a doublet and a triplet respectively, when chemical exchange operates.

 

 

19. Explain isotropic and anisotropic hyperfine splitting with examples.
20. While isomershift is a function of S electron density, quadrupole splitting is not so – Explain.
21. What is pure NQR? Is pure NQR enough to calculate the quadrupole parameters in the case of ¹⁴N containing compound?
22. Sketch the EPR spectrum of i) H₂⁺ ii) D₂⁺

PART C

Answer any four questions:                                                                                                   4×10=40

23. Draw and explain Morse curve for an anharmonic oscillator.
24. Assume the following data for the molecule ¹H³⁵Cl:

Bond length:127.5pm, Bond force constant : 516.3Nm^-1,

Atomic masses: ¹H = 1.673×10^-27kg, ³⁵Cl = 58.06 x10^-27kg

Calculate the following and give answers in cm^-1

1. Zero point energy and the energy of fundamental vibration
2. Rotational constant B
3. Wave numbers of the lines P₍₁₎, P₍₂₎, P₍₃₎, R₍₀₎, R₍₁₎, R₍₂₎
4. Discuss the principle of diatomic non-rigid rotor with an example.
5. a) The NQR frequencies for ²D in a compound are γ₊ = 6 kHz and γ_– = 5 kHz respectively. Calculate the asymmetry parameter η and the quadrupole coupling constant.
6.  b) Explain the principle of FAB mass spectrometry.
7. a) Acetylenic protons are more shielded than ethylenic protons. – Justify.
8. b) What is COSY? Discuss the COSY of 1,3-dichloro propane.
9. a)How will you determine the oxidation state of an element using Mossbauer spectroscopy?
10. b) What is ‘g’ shift in EPR? How does it help to know the delocalization of

electron in a molecule?

 

 

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