No. of Printed Pages: 8 ICHE-IOI
BACHELOR OF SCIENCE (B.Sc.)
Term-End Examination

June, 2016
CHEMISTRY
CHE-10 SPECTROSCOPY

Time: 2 hours Maximum Marks: 50
Note: Attempt any five questions. All questions carry equal marks.

(ii) Use of log tables and non-programmable scientific calculators is allowed.

Take: h 6.626 x 10^-34 Js

1. Write the term symbols for 3p^l configuration of sodium. Hence, explain what are D lines in the spectrum of sodium. 3

Using VSEPR theory, predict the shape of XeF4• 3

Identify various symmetry elements present in BF3 and assign the point group to which it belongs. 4

2. Which of the following molecules will exhibit rotational spectrum and why?

CO2, HF, N2O, H2O, CS2,SO2 3

The transition from J 0 to 1 for HCI takes place at v 22.18 . What is the bond length of 1H^35Cl (Use atomic masses as H 1 Cl 35 3

What is the selection rule for a rotational transition in a rigid diatomic molecule Though all such transitions are equally probable, the intensity of the lines are not equal. Explain. 4

3. Draw and explain a typical vibrational-rotational spectrum of a diatomic molecule with proper labelling of Q and R branches. 3

Draw a block diagram for a microwave spectrometer. 3

Illustrate with suitable diagrams, the normal modes of vibrations of a linear triatomic molecule AB2. Which of these modes will be IR active? 4

4. What is Raman spectrum What is the essential criterion for a molecule to be Raman active? 2

A triatomic molecule, AB2, showed the following spectral data

cm^-1 IR Raman
1595 v. strong, observed,
parallel polarized
3651.7 strong, strong,
perpendicular polarized
3755.8 v. strong, observed,
parallel depolarized

Deduce its structure stating the principle used. 4

The dissociation energy for chlorine molecule in the ground state is 239 kJ mol^-1. If the excitation energy for chlorine is 881 compute the continuum vibrational wave number for chlorine molecule. 4

5. Illustrate and explain the ESR spectrum of hydrogen atom. 3

Draw and explain the NMR spectrum of ethyl bromide. 3

The eg orbitals are higher in energy than the t2g orbitals in octahedral arrangement but the order is reversed in tetrahedral arrangement. Explain. 4

6. State the basic principle of mass spectrometry. 3

The IR, NMR and mass spectra of a compound with molecular formula C9H10O2 showed the following results

Mass spectrum: m/z 150 91, 43

IR 1740, 1220, 1600 -1400, 749 and 697

NMR CDCl3) 1.96 5.0 7.22 5H)

On the basis of the above data, deduce the possible structure of the molecule. 7

7. Write short notes on any two of the following: 2x3=6 Spin-spin coupling

(ii) Effect of solvent on n and T transitions

(iii) McLafferty rearrangement
Explain the difference between fluorescence and phosphorescence. 4