M.Sc. (Semester III) (CBCS) Examination Nov/Dec-2018
Physical Chemistry
MOLECULAR STRUCTURE I
Time: 2½ Hours
Max. Marks: 70
Instructions: Attempt in all five questions. Question one is compulsory. Answer to all questions should be written in the same answer book. All questions carry equal marks. Figures to right indicate marks. Neat and labeled diagrams should be drawn. Use of log table and calculator is allowed.
Q.1
Multiple choice questions:
14
Identify the pint group of square planar PtCl42- ion.
C2h
C3v
D∞h
D4h
Which of the following molecule belongs to Td point group?
NH3
SiF4
Benzene
Pyridine
−1000−10001
The following transformation matrix represents operation.
C2
C3
C4
C6
For a non-rigid rotator the spacing between the first two lines of rational spectrum is
2B- 4D
2B- 8D
6B- 8D
2B- 20D
The expression for rotational energy of a oblate symmetric top molecule is EJ




The value of J for the maximum population of rotational energy levels of a molecule is given by Jmax=
√ [kT/2hcB]
√
√
√ [2kT/hcB]
The lowest energy of a harmonic oscillator is equal to
hωosc
2hωosc
ωosc
(1/2)hωosc

If the rotational constant H2 molecule is B what will be the rotational constant of D2 molecule?
2B
B/2
B


Total number of vibration in CH3COOH
14
16
18
19
10) The fundamental bands in IR spectroscopy are obtained due to excitation of molecule from V state.
0
1
2
3
11) The term symbols for a state 1 and 2
3P1,3P3 and 3P1
3P2, 3P1 and 3P0
2P2, 2P1 and 2P0
P2,P1 and P0
12) Which transitions of an organic molecule are generally observed in the visible region?
to π∗
σ to π∗
σ to
n to π∗
13) A molecule of the formula XY2 has three bands active both in IR and Raman then its structure is




14) The Birje- Sponer plot for a molecule is a graph of Δε against
J
v and J
v
Δ v
Q.2
a)Answer the following (any four)
08
How do you represent identity operation by a transformation matrix?
What are Anti- Stokes lines?
If a molecule of the formula XY2 and does not contain centre of symmetry. How many IR and Raman active bands will be observed?
Why the rotational constant of a non-rigid rotator decreases as J increases as compared with that of rigid rotator?
Differentiate between and progressions.
b)Write notes on (Any two)
06
Reducible and irreducible representations
Natural line width
Russell- Saunders coupling
Q.3
a)Answer the following(Any two)
08
Verify the orthogonality theorem for the character table of C2V group.
Discuss the effect of isotopic substitution on rotational spectra of a diatomic rigid rotator.
Discuss the physical origin of line widths in electronic spectra of molecules.

Answer he following (Any one)
06
Give an account on fundamental vibrations of water and their symmetry.
Explain the terms predissociation and dissociation energy.

Q.4
a)Answer the following (Any two)
10
Discuss the classification of molecules into various point groups.
Derive expression for Jmax for a rigid diatomic molecule assuming the degeneracy of its rotational energies is
The first line of the R branch of IR spectrum of HCl is observed at 2907.23cm-1. If its fundamental band is observed at 2886 cm-1. Calculate the rotational constant of the molecule.
b)Answer the following (Any one)
04
For a symmetric top molecule obtain expression for the frequencies of IR spectrum of parallel vibrations.
What is Stark effect? Obtain expression for the first correction to the transition frequencies.
Q.5
Answer the following (Any Two)
14
a)For a linear triatomic molecule explain the method of determining bond lengths by isotopic substitution of any one atom.
b)Explain how do the band heads P and R arise in a vibration-electronic transition of a diatomic molecule.
c)What are term symbols? How they are represented?