LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

SECOND SEMESTER – APRIL 2006

                                               CH 2950 – MOLECULAR SPECTROSCOPY

(Also equivalent to CH 2802)

Date & Time : 21-04-2006/FORENOON     Dept. No.                                                       Max. : 100 Marks

Part-A   ANSWER ALL QUESTIONS (10 x 2 = 20)

1. Indicate which one will have higher λ_max value and explain

• CH₂ = CH₂ and CH₂ = CH – CH = CH₂
• C₆H₆ and C₆H₅OCH₃

2. The ¹H NMR of C₄H₉Cl gave a single peak at 1.80 δ as a singlet. Give the structure of the compound.
3. Sketch the EPR spectrum of C₆H₅^• radical and explain.
4. Which one has a higher ν(C=O) value? Explain

O                                                O

||                                                  ||

CH₃ – C – CH₃       and    CH₂ = CH – C – CH₃

5. How is the mass of metastable peak calculated in the mass spectrum? Explain with one example.
6. Identify the point groups for the following molecules:

(a)POCl₃    (b) SF₆     (c) Br₂          (d) Ni(CN)₄^2- (square planar)

7. Explain the rule of mutual exclusion with a suitable example.
8. Explain the spectroscopic transitions (a) fundamental (b) hot bands using proper quantum
9. Explain the meaning and significance of x, y, and z in the T₂ representation of the T_d point group as shown below

T_d      E          8C₃      3C₂      6S₄       6σ_d

T₂      3          0          -1         -1         1          (x,y,z)

10. Identify the symmetry operations present in the point groups C₁, C_i, and C_s. Give one example for each.

Part-B   ANSWER ANY EIGHT QUESTIONS (8 x 5 = 40)

11. How does the solvent polarity affect the λ_max of the compound?
12. How are the following differentiated by the infrared spectral studies?

• aliphatic and aromatic compounds
• ethanol and diethyl ether (3+2)

13. Write a note on Nuclear Overhauser effect.
14. Sketch the Mossbauer spectrum of [Fe(CN)₆]^3- and explain.
15. Discuss the detectors used in UV-Visible double beam spectrophotometer.
16. Discuss the McLafferty rearrangement in the mass spectral fragmentation pattern.
17. Explain the factors for the broadening of spectral lines.
18. How are P, Q, and R branches of absorption bands obtained in vibration-rotation spectra of molecules? In which type of molecules Q branch is not observed and why?
19. (a) When do we say two symmetry operations are in the same class? Explain with an example.
    • The equilibrium vibration frequency of the HBr molecule is 2649.7 cm^-1 and the anharmonicity constant is 0.0171; what, at 300K, is the intensity of the ‘hot band’ (v=1 to v=2 transition) relative to that of the fundamental (v=0 to v=1)?    (2+3)

20. A microwave spectrometer capable of operating only between 60 and 90 cm^-1 was used to observe the rotational spectra of HI. Absorptions were measured as follows:

Find B, I and r for each of the molecule, and determine the J values between which transitions occur for the first line listed above.

21. (a) Explain the following with a suitable molecule for each:

(i) Principal axis of rotation    (b) Inversion Center

(b) Explain the meaning of a E_g representation in the character table.  (2+2+1)

22. Give the reduction formula and reduce the following reducible representation.

C_2h      E          C₂        i          σ_h          

8          0          6          2

C_2h       E          C₂        i           σ_h

A_g        1          1          1          1          R_z              x², y², z², xy

B_g           1          -1         1          -1         R_x, R_y        xz, yz

A_u        1          1          -1         -1         z

B_u        1          -1         -1         1         x, y

Part-C   ANSWER ANY FOUR QUESTIONS (4 x 10 = 40)

23. How are the UV-Visible spectral studies useful in (a) charge-transfer transition
    (b) electronic effect in the organic molecules? (5+5)
24. Describe the following:

• Proton noise decoupled ¹³C-NMR
• Spin-spin coupling in ¹H NMR                                                               (5+5)

25. Discuss the principle and instrumentation involved in the EPR spectroscopy. Explain the nuclear hyperfine splitting. (4+3+3)
26. (a) State and explain Franck-Condon Principle. How are intensity variations of electronic spectra explained by this principle?

(b) The Bond length of NO is 115.1 pm. Bond force constant is 1595 Nm^-1. Calculate (a) Zero-point energy and the energy of the fundamental vibration ν₀.
(b) Calculate the rotational constant B. (c) Calculate the wave numbers of the lines P₁, P₂, R₀ and R₁                                                                                      (5+5)

27. (a) What are Stokes and anti-Stokes lines and Rayleigh lines? Compare their intensities in the Raman vibrational spectrum of a compound.

(b) Consider the molecules N₂, CCl₄, CH₃Cl and H₂O. Predict which of them will show (a) Pure rotational spectrum (b) infrared absorption (c) electronic transition. Give reasons for your choice.                                                                      (5+5)

28. Find the number, symmetry species of the infrared and Raman active vibrations of CH₄, which belongs to T_d point group. State how many of them are coincident.

(You may, if you wish, use the table of f(R) given below for solving this).

T_d         E          8C₃      3C₂      6S₄       6σ_d

A₁        1          1          1          1          1                                  x²+y²+z²

A₂        1          1          1          -1         -1

E          2          -1         2          0          0                                  (2z²-x²-y², x²-y²)

T₁         3          0          -1         1          -1         (R_x,R_y,R_z)

T₂         3          0          -1         -1         1          (x,y,z)              (xy,xz,yz)

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                          LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

THIRD SEMESTER – NOV 2006

CH 3810 – MOLECULAR SPECTROSCOPY

Date & Time : 30-10-2006/9.00-12.00      Dept. No.                                                   Max. : 100 Marks

PART A

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

1. Convert 0.15 nm to Hz and state what sort of transition this corresponds to.
2. What are stokes and anti-stokes lines?
3. Name two techniques to enhance the sensitivity of the spectral lines.
4. What is the basic principle of Mossbauer spectroscopy?
5. From the relative abundance of the (M+2)⁺ peaks in the mass spectra, can you distinguish chloro compounds from Bromo compounds?
6. State the principle of PES. What is the essential difference between XPES and UV-PES?
7. A free electron is placed in a magnetic field of strength 1.3 T. If g_e is 2.0023 and β_e is 9.274 x 10^-24 JT^-1. Find the ESR frequency in GHz.
8. What are the advantages of using TMS as the standard in NMR experiments?
9. Compare the ¹H and ¹³C NMR spectra in terms of the range of chemical shifts and intensity of the peaks (peak areas)
10. What is spin-spin relaxation?

PART – B

Answer ANY EIGHT questions                                          (8 x 5 = 40 Marks)

11. What are the factors that affect the width of the spectral lines? Explain any two of them.
12. The observed infrared absorption and Raman spectral lines of Chlorate ion (ClO₃^–) are given below. Predict the structure of Chlorate ion.

13. The frequencies of vibration of the following molecules in their v = 0 states are HCl: 2885 cm^-1; D₂: 2990 cm^-1; DCl: 1990 cm^-1 and HD: 3627 cm^-1, calculate the energy change in the reaction HCl + D₂ à DCl + HD.
14. The mass spectrum of a compound having the empirical formula C₁₁H₁₂O₂, shows the following peaks at m/e : 78,105 (Base peak), 122, 135,176 (Molecular Peak). Identify the compound and account for the fragments.
15. At what temperature will the number of I₂ molecules in the v=1 level be one-tenth of that in the v=0 level? Given = 214.6 cm^-1;x_e = 0.6 cm^-1 and k = 1.38 x 10^-23J K^-1.
16. Explain Quadrupole mass spectrometer.
17. Explain what is Zero Field or Crystal Field Effect in the fine structure of ESR

and the factors that contribute to that.

18. State and explain Franck-Condon Principle. With diagrams explain the

variations in intensity of electronic spectra explained by this principle?

19. What is population inversion? Prove that a population inversion cannot

be achieved in a two level system while it is possible in a three level system.

20. (a) With an example explain Diamagnetic Anisotropy.

(b) The chemical shift of the CH₃ protons in diethyl ether is ∂ = 1.16 ppm and that of the CH₂ protons is 3.36 ppm. What is the difference in local magnetic fields between the two regions of the molecule when the applied field is 16.5 T?

21. Predict

(a) the spin-spin splitting pattern for the protons of neopentane molecule

and the peaks’ intensity distribution.

(b) the hyperfine splitting of the ESR spectrum of ۰CD₃ and ۰CHD₂ radicals.

[note: the spin of D is 1]

22. Explain the principle of 2D NMR highlighting its advantages.

PART – C

Answer ANY FOUR questions                                            (4 x 10 = 40 Marks)

23. a) Three consecutive lines in the rotational spectrum of a diatomic molecule are observed at 84.544, 101.355 and 118.112 cm^-1.  Assign these lines to their appropriate J^’’ àJ^’ transitions and deduce the values of B and D.
24. b) How are meta stable ions produced and how are they useful in identifying the molecular formula of a compound?
25. a) The fundamental band of HCl is centered at 2886 cm^-1.  Assuming that the internuclear distance is 12.76 nm, calculate the wave number of the first two lines of each of the P and R branches of HCl.
26. b) Explain the pure rotational spectra of symmetric top molecules.
27. a) Explain the fact that the Mossbauer spectrum of [Fe(CN)₅NO]^2- gives two lines whereas [Fe(CN)₆]^4- spectrum gives one line.
28. b) In the rotational Raman spectrum of HCl, the displacements from the exciting lines are represented by Dn = ± (62.4 + 41.6 J) cm^-1.  Calculate the moment of inertia of the HCl molecule.
29. Explain the following with a suitable example:

(a) spin-spin coupling in ¹H-NMR

(b) mechanism of spin-spin coupling for geminal protons

(c) the multiplicity and intensity distribution represented by the ‘coupling tree’

27. (a) Explain briefly: (a) spin-spin relaxation (b) Fourier Transformation Technique.

(b) Sketch the esr spectrum of ^°CH₃ and explain its nuclear hyperfine splitting.

28. (a) What are asymmetry electric field gradient and asymmetry parameter, η? How

are they related? What is the significance of η?

(b) Taking any laser as example explain the three most important components

of a laser?

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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

THIRD SEMESTER – APRIL 2008

CH 3810 – MOLECULAR SPECTROSCOPY

Date : 02-05-08                  Dept. No.                                        Max. : 100 Marks

Time : 9:00 – 12:00

Part A

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

1. What is ‘resolving power’ of a spectrometer? Mention any one method of improving it.
2. The first line in the rotation spectrum of CO appears at 3.84235 cm^-1. Calculate its

moment of inertia.

3. CO₂ gives two IR absorptions although the molecule has no dipole moment. Why?
4. Explain the principle of mutual exclusion with an example.
5. Mention three important characteristics of lasers which differ from ordinary light.
6. State nitrogen rule.
7. How many signals are expected in the ESR spectrum of isopropyl radical?
8. Write any four advantages of using tetramethyl silane as internal reference compound in recording NMR spectra.
9. An organic compound (molecular formula C₄H₁₀O) contains a triplet centered at ∂ = 1.26 ppm and a quartet at ∂ = 3.38 ppm in its ¹H NMR spectrum. Write the structure of the NMR spectrum. Write the structure of the compound.
10. Acetylenic proton absorbs at upfield compared to ethylenic proton, although the former is attached to a more electronegative carbon. Explain.

PART – B

                                        Answer ANY EIGHT questions              (8 x 5 = 40 Marks)

11. What are the factors governing the intensity of the spectral lines? Explain any two of them.
12. Consider the molecules Br₂, HCl, CCl₄. Which of these will give a pure

(a) rotational microwave spectrum? (b) infrared spectrum?  (c) Raman spectrum

(d) electronic spectrum?

13. The Bond length of ¹H⁸¹Br is 141.44 pm. Bond force constant is 411.5 Nm^-1. Calculate the zero-point energy, the energy of the fundamental vibration ν₀, the rotational constant B and the wave numbers of the lines P₁, P₂, R₀ and R₁
14. State and explain the Franck-Condon Principle. How are the intensity variations of electronic spectra explained by this principle?
15. With an example explain the three most important components of a laser?
16. (a) State the principle of PES. What is the essential difference between XPES and UV-PES?

(b) With an example explain how PES can be applied to molecular structure.    (2+3)

17. What are the sample requirements in NQR spectra? Illustrate the application of NQR

spectra with one example. What is the main drawback of this technique?

18. Discuss hyperfine splitting by taking the ESR spectrum of methyl radical. Sketch the

energy level diagram and indicate the transitions responsible for ESR signals.

19. Discuss the principle of ¹³C NMR spectra and explain two of its applications in the

determination of structure of organic compounds.

20. Write briefly on ‘Lanthanide shift reagents’.
21. Describe the various parts of mass spectrometer and explain the function of each part.
22. Discuss the theory of Mössbauer spectra.

PART – C

                                                     Answer ANY FOUR questions               (4 x 10 = 40 Marks)

23. a) Discuss the factors contributing to the broadening of the spectral lines.                (6)
24. b) The stretching frequency of ¹²C¹⁶O occurs at 2143 cm^-1. Calculate the force constant for this molecule. Assuming the force constant to be the same for ¹²C¹⁷O, calculate the stretching frequency for ¹²C¹⁷                                                                      (4)
25. a) Explain the origin of P, Q, R branches of the rotation-vibration spectra with a diagram. (5)
26. b) Differentiate the origin and nature of Stokes’ lines, Anti-Stokes’ lines and Rayleigh scattering with respect to their position in spectrum and the intensity of the spectral lines. (5)
27. a) What is population inversion? Show that a population inversion can be

achieved in a three level system.          (6)

5416. b) The ionization energy for 3s electron is 30 eV. The kinetic energy of electrons ejected is 5416.07 eV. Find the wavelength of X-rays used for this PES experiment. (1eV = 1.602 x 10^-19J) (4)
5417. a) What is meant by geminal coupling? Explain with suitable examples the effect of hybridization of carbon and the elctronegativity of substituent on the germinal coupling constant. (5)
5418. b) Illustrate long range coupling through п-bond and W–coupling with suitable examples. (5)
5419. a) ESR is observed for atomic hydrogen with an instrument operating at 9.5 GHz. If

the ‘g’ value for the electron in hydrogen atom is 2.0026, what is the strength of the

applied magnetic field? (1 GHz = 10⁹ Hz, μ_e = 9.274 x 10^-24 JT^-1)                        (4)

(b) Describe the FAB technique for the production of molecular ions in mass

spectrometer. What are its advantages and limitations?         (6)

28. (a) Write briefly on ‘McLafferty rearrangement’. (4)

(b) An organic compound with molecular formula C₄H₉Br contains the following

signals in 1H and ¹³C NMR spectra:

PMR data: (a) doublet    ∂ = 1.04 ppm (6H)

(b) multiplet ∂ = 1.95 ppm (1H)

(c) doublet    ∂ = 3.33 ppm (2H)

CMR data: (a) quartet    ∂ = 20.9 ppm

(b) doublet  ∂ = 30.7 ppm

(c) triplet     ∂ = 42.2 ppm

Assign a suitable structure to the compound and explain the NMR spectral data.   (6)

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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

THIRD SEMESTER – November 2008

    CH 3810 – MOLECULAR SPECTROSCOPY

Date : 07-11-08                 Dept. No.                                        Max. : 100 Marks

Time : 9:00 – 12:00

PART A

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

1. Convert 500 nm to cm^-1 and state what sort of transition this corresponds to.
2. What is the resolving power of a mass spectrometer?
3. Define Stokes and anti-Stokes’ radiation.
4. The rotational constant of CO molecule is 1.9313 cm^-1. Determine the transition which gives the most intense spectral line at 300 K.
5. How will you distinguish between (CH₃)₃N and CH₃CH₂CH₂NH₂ by infrared spectroscopy?
6. The magnetic moment vector executes Larmor precession instead of aligning with the magnetic field.
7. Mention any two differences between continuous wave and FT NMR methods.
8. Identify the isomer of C₃H₇ radical which showes 14 lines in its EPR spectrum.
9. Sketch the EPR spectrum of cyclobutyl radical anion C₄H₇
10. Phosphorescence unlike fluorescence cannot be studied in liquid phase. Explain.

PART – B

Answer ANY EIGHT questions                                          (8 x 5 = 40 Marks)

11. What are Einstein’s coefficients? Derive the relation between them.
12. Irradiation of CCl₄ by 435.8 nm radiation gives the Raman lines at 440, 441.9 and 444.7 nm. Calculate the Raman shift for each of these lines.
13. Explain Fourier transform infrared spectrometer.
14. The mass spectrum of an organic compound having the empirical formula C₄H₉NO exhibits peaks at m/z 87 (Molecular ion peak), 86, 72, 71, 59, 44 (base peak) and 43. Predict the structure of the compound and account for the fragments mentioned above.
15. The observed infrared absorption and Raman spectral lines of Nitrate ion (NO₃^–) are given below. Deduce the structure of Nitrate ion and assign the frequencies to particular fundamental modes.

16. The rotational and centrifugal constants of HF¹⁹ molecule are 20.56 cm^-1 and 00213 cm^-1. Estimate the vibrational frequency and the force constant of the molecule.
17. How is FID signal obtained? Mention its significance.
18. What is allylic coupling? Account for the maximum and minimum value of allylic coupling constant.

19. Explain the use of EPR technique to understand the delocalization of electrons in complexes.
20. What are coherence time and coherence length?
21. Explain how Frank-Condon principle accounts for the intensity variations in electronic spectra.
22. Discuss the effect of magnetic field on the NQR spectra of systems with nuclear spin 1 and 3/2.

PART – C

Answer ANY FOUR questions                                            (4 x 10 = 40 Marks)

23. a) Calculate the energy in Joules of the photon absorbed when ¹⁴N¹⁶O molecule goes from the state v=0, J^’’=0, v= 1, J^’ = 1. Assume that v = 0 and v = 1 states have the same B values.  Given   (cm^-1) = 1904 cm^-1; x_e = 0.00733, r_NO = 0.1151 nm                                 (5)
24. b) Explain the pure rotational spectrum of symmetric top molecule             (5)
25. a) The first three rotational Raman lines of a linear triatomic molecule are at 4.86, 8.14 and 11.36 cm^-1 from the exciting Raman line.  Estimate the rotational constant B and the moment of inertia of the molecule in kg m².                                                                                (4)
26. b) Briefly discuss the MALDI-TOF mass spectrometry                                          (6)
27. a) Explain isomer shift in Mossbauer spectroscopy with an example.                      (4)
28. b) The fundamental band of ²D³⁵Cl is centred at 2011 cm^-1.  Assuming that internuclear distance is constant at 12.88 nm, calculate the wave numbers of the first two lines of each of the P and R branches of DCl                                                                                                                  (6)
29. (a) Explain the principle and interpretation of COSY of a compound                (6)

(b) Calculate the chemical shift, when the frequency of separation between protons of a compound and TMS is 540 Hz at a magnetic flux density of 1.85 T (g_N = 5.585)                    (4)

27. (a) How will you account for the difference in the g-value of free radicals with transition metal complexes                                     (6)

(b)  Calculate the g-value for p⁵ configuration                                                            (4)

28. (a) Discuss the theory of NQR spectroscopy (5)

(b) Explain the broad band absorption and fluorescence exhibited by  the dye-Rhodamine 6 G                                                                                                                                    (5)

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        LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

THIRD SEMESTER – April 2009

CH 3810 – MOLECULAR SPECTROSCOPY

Date & Time: 04/05/2009 / 9:00 – 12:00  Dept. No.                                                   Max. : 100 Marks

PART A

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

1. What is S/N ratio? How can it be enhanced?
2. The rotational constant of a rigid diatomic molecule is 1.566 cm^-1. Determine the transition which gives the most intense line at 300 K.
3. Differentiate between hot band and overtone in the nature of their transitions.
4. From the relative abundance of the (M+2)⁺ peaks in the mass spectra, can you distinguish Chloro compounds from Bromo compounds.
5. What is the basic principle of Mossbauer Spectroscopy?
6. Calculate the Larmor precessional frequency of a proton when placed in a magnetic field strength of 1.5 T ( g_N = 5.585)
7. What are diagonal and off-diagonal peaks in 2DNMR.
8. Sketch the EPR spectrum of HCl radical.
9. What are the conditions to observe NQR transitions.
10. Mention the importance of a saturable absorber dye.

PART – B

Answer ANY EIGHT questions                                          (8 x 5 = 40 Marks)

11. Explain the factors that affect the intensity of spectral lines.
12. The rotational spectrum of ¹²C¹⁶O shows a series of equidistant lines spaced 3.8424 cm^-1 Calculate the rotational constant and the C-O bond length in this molecule.
13. Explain the pure rotational Raman spectrum of a symmetric top molecule.
14. A molecule AB₂ has the following IR and Raman spectra. Discuss the molecular structure and assign the observed lines to molecular vibrations.

15. Calculate the recoil velocity of the free Mossbauer nucleus ¹¹⁹Sn when emitting a γ- ray of frequency 5.76 x 10¹⁸ What is the Doppler shift of the γ- ray frequency to an outside observer?
16. The mass spectrum of a compound having the empirical formula C₅H₈O₂, shows the following peaks at m/e : 28, 43 (Base peak), 85, 100 (Molecular Peak). Identify the compound and account for the fragments.
17. What is the effect of shielding and deshielding on precessional frequency?
18. Odd number of bonds give positive J vale while even number of bonds give negative J values – explain.
19. Discuss the EPR spectrum of a triplet state radical.

20. Calculate the NQR frequency of a compound that has a C₃ axis of symmetry. Given that e = 4.8 x 10^-10 esu, Q = 0.08 x 10^-24 cm² and q = 2 x 10²⁵
21. How is pulse operation achieved in Q-switching?
22. Explain the mechanism of mode locking method of producing laser pulses.

PART – C

Answer ANY FOUR questions                                            (4 x 10 = 40 Marks)

23. a) The fundamental and first overtone transitions of  ¹H³⁵Cl are centered at 2886 cm^-1 and 5668 cm^-1  Evaluate the equilibrium vibration frequency, the anhormonicity constant, and the force constant of the molecule.                                                  (6)
24. b) Give any four basic differences between IR and Raman spectra                                    (4)
25. a) The fundamental band of ¹⁴N¹⁶O is centred at 1904 cm^-1 and its bond length is 0.1151 nm. Calculate the rotational constant B and the first two lines of the P and R branches of the vibration-rotational spectrum of NO.                                                                   (6)
26. b) Explain briefly Quadrupole Mass analyzer.                                                         (4)
27. a) Discuss any two applications of Mossbauer spectroscopy.                                  (6)
28. b) The Raman line associated with a vibrational mode which is both Raman and IR active is found at 460 nm when excited by light of wavelength 435.8 nm. Calculate the wavelength of the corresponding infrared band.                         (4)
29. (a) How will you interpret the Hetero nuclear correlation spectrum of a compound?(6)

(b) NMR of benzene is observed at a lower field while acetylene is at a higher field – explain                                                                                                             (4)

27. (a) Explain the importance of the following (i) Electric field gradient (ii) asymmetry parameter                                                                                                           (6)

(b)  The benzene radical anion has a g value of 2.0025.  At what field would you search for resonance in 9.525 GHz instrument.                                                                 (4)

28. (a) How will you characterize the delocalization of an unpaired electron in a transition

metal complex?                                                                                                     (5)

(b) How will you account for the variation in intensity of electronic transitions?     (5)

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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

THIRD SEMESTER – NOVEMBER 2010

    CH 3810  – MOLECULAR SPECTROSCOPY

Date : 03-11-10                 Dept. No.                                        Max. : 100 Marks

Time : 9:00 – 12:00

Part – A

Answer all the questions                                                                                                  (10 x 2 = 20)

1. Calculate the wavelength of a ball with 10 g mass and velocity , 2000 ms^-1.
2. What do you mean by computer averaging enhancement of spectra?
3. What are Rayleigh ad Raman scattering?
4. Differentiate phosphorescence and fluorescence properties of excited molecules
5. What is photoelectric effect?
6. The NMR frequency of protons in a magnetic field intensity of 1T is 42.57 MHz.

Calculate the nuclear g factor for protons.

7. Vicinal coupling is minimum at 90º dihedral angle – why?
8. Sketch the EPR spectrum of CD₃ radical.
9. Mention the conditions to observe NQR transitions.
10. How will you obtain Mossbauer spectrum of a liquid sample?

Part – B

Answer any EIGHT questions                                                                                              (8 x 5 = 40)

11. Explain briefly the factors affecting the intensity of spectral transitions?
12. . Discuss the effect of isotopic substitution in the rotational spectrum of non rigid diatomic molecule.
13. Explain the principles of non-linear optical effects and frequency generation by them.
14. The exciting line is 5650 A⁰ and the Stokes line is 5800 A⁰. Calculate the wavelength of the anti-Stokes line.
15. Describe the vibrational spectrum of the anharmonic oscillating diatomic molecule
16. How does mutual exclusion principle help in resolving the geometry of chemical molecules?
17. How will you account for the positive and negative coupling constants in NMR?

18. How are the following identified in 2D NMR?
    • non-adjacent groups
    • long range coupling
19. EPR spectra are not presented as an absorption curve – Explain.
20. Explain the following
    • asymmetric parameter in  NQR
    • pure NQR
21. Discuss the chemical ionization technique with suitable example.
22. Explain McLafferty rearrangement with an example.

Part C

Answer any FOUR questions                                                                                  (4 x 10 = 40)

23. a) How are the rotational energy states determined by the magnitude of moment of

inertia for  diatomic non-rigid rotor molecule?   (5)

1. b) Calculate the rotational constant of  The bond length is 136 cm^-1.  (5)

24. a) How are the vibrational energy states determined for simple harmonic diatomic

molecule?  (5)

b)The bond length of ClF molecule is 0.1630 nm and the centrifugal distortion constant

is 10^-4 B. Calculate the spacing between first eight lines.  (5)

1. Explain the principles of Raman effects by i) Quantum theory ii) Classical theory.

26. a) What is a HETCOR spectrum? How will you interpret it? (6)
27. b) Distinguish between paramagnetic and diamagnetic anisotropy. (4)

27. a) Explain zero field splitting and hyperfine interaction in EPR with suitable examples. (6)
28. b) Draw an energy level diagram showing the ESR spectrum of an odd electron and compare it with the NMR spectrum of a bare proton. (4)

28.a) Explain isomer shift and quadupole splitting with relevant examples. (6)

1. b) How is X-axis is mass spectrum is calibrated in terms of m/e? What is the significance of molecular ion peak?   (4)

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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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