PG – 112

*PG112*

IV Semester M.Sc. Examination, June 2015 (NS) CHEMISTRY C-404 : Spectroscopy – III (Common to IC/PC/AC) Time : 3 Hours

Max. Marks : 80

Instruction : Answer Q. No. 1 and any five of the remaining. 1. Answer any ten of the following :

(10×2=20)

a) How is the possibility of NO2 being linear ruled out on the basis of IR data ? b) The IR spectrum of KrF2 has bands at 233 and 588 cm–1, the Raman spectrum displays a single band at 499 cm–1. Give the structure of KrF2. c) The C (1s) binding energy is higher in CO2 than in CO, but the O (1s) binding energy is lower. Account for these observations ? d) Obtain an expression for the calculation of energy for the conversion of a molecule into its ion (M → M+) in PES. e) Predict and sketch 31P NMR spectrum of HPO(OH)2 and H2PO(OH) assuming JP–OH to be negligible. f) The 19F NMR spectra of equimolar quantities of TiF62– and TiF4 in ethanol shows two peaks with intensity ratio 4 : 1. Explain with its structure. g) Calculate the g1 and g11 values for a CuC(1) complex if the resonances occurred at 3214 and 3071 G respectively and for the reference at 3286 G. g value for the reference is 2.0037.

h) How many ESR lines are expected in the spectrum of .CD3 radical ? What are their relative intensities ? .. i) The Mo ssbauer spectrum of Fe(CO)5 shows splitting but that of K4Fe(CN)6 doesn’t. Why ? j) How many resonances are expected in the NQR spectrum of nuclei with I = 5/2 when η = 0 ? Sketch the energy levels. k) The 35Cl e2Q9 of KCl and FCl are 0.04 and –146.0 respectively. Account for this variation. l) What is the significance of EXAFS ? P.T.O.

PG – 112

-2-

*PG112*

2. a) Explain how are the following distinguished using IR spectra : i) S– and N– bonded thiocyanate complexes. ii) nitro– and nitrite complexes. b) What differences in the number of bands and frequencies are expected between C – O absorptions of the following : acetate ion, acetic acid, silver acetate and acetate bound to zinc as a bidentate ligand. c) How does the critical absorption edge arise ? Point out its significance. (4+5+3=12) 3. a) What is resonance Raman effect ? Discuss the advantages of resonance Raman spectrum over normal Raman spectrum. b) How does inverse Raman effect arise ? How does it differ from stimulated Raman effect ? c) Sketch the photoelectron spectrum of N2- molecule and explain the observed pattern. (5+3+4=12) 4. a) The photo-ionization of F2 by He(I) produces F2+. Explain why the intensity of υ = 0 → 2 transition is stronger than that of 0 → 0 transition. b) What is Auger process ? What information can be obtained from an Auger spectrum ? c) How does a photo acoustic spectrum arise ? Mention any one application.

(5+4+3=12)

5. a) In the 1H NMR spectral studies of HIrCl2(Et3P)3 one isomer shows only one coupling constant (15Hz) whereas the other isomer shows two coupling constants (19 and 163 Hz). Explain. b) What are the possible structures of ClF3 ? How are these possibilities resolved by using 19F NMR spectrum ? Explain. c) Predict the 31P NMR spectra of fac– and mer – [RhCl3(PPh3)3] and explain the patterns. (4+4+4=12)

*PG112*

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PG – 112

6. a) What is zero-field splitting ? How does it arise ? Explain its consequences in the ESR spectrum of a d2– ion. b) How does anisotropy arise in ‘g’ values ? Explain. c) Calculate the magnetic field at which the resonance occurs if the ‘g’ value of the benzene radical anion is 2.0025 and the ESR spectrometer is operating at (5+4+3=12) 9302 MHz. (h = 6.626×10–34 Js, β = 9.2741×10–24J T–1). .. 7. a) How are the following distinguished by Mo ssbauer spectroscopy ? i) SnCl2 and SnCl4 ii) K2[Fe(CN)5 (NH3)] and FeCl3.6H2O. b) How are recoillers emission and resonant reabsorption of γ -rays achieved in .. Mo ssbauer spectroscopy ? c) Outline the principles of NQR spectroscopy and explain its importance in distinguishing ionic and covalent bonds. (4+4+4=12)

_______________________

Spectroscopy – III.pdf

3. a) What is resonance Raman effect ? Discuss the advantages of resonance. Raman spectrum over normal Raman spectrum. b) How does inverse Raman ...

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