M.Sc. (Semester III) (CBCS) Examination Mar/Apr-2018
Physical Chemistry
MOLECULAR STRUCTURE I
Time: 2½ Hours
Max. Marks: 70
Instructions: Attempt in all five questions. Section-I is compulsory. Attempt any two questions from Section-II and any two questions from Section-III. Answer to all questions should be written in same answer book. All question carry equal marks. Figures to the right indicate full marks. Use of calculator and log table is allowed.
Section I
Q.1
Answer the following.
14
The geometric rearrangement which moves the molecular framework from its original position to a new physically indistinguishable position is called
For a planar MX4molecule, two successive C4operations is equal to one operation.
For a rigid rotator the spacing between the lines of rotational spectrum is
Write the expression for rotational energy of a prolate symmetric top molecule.
The rotational frequency, of a diatomic molecule is 6.28×1012 radians s−1. What will be its period of rotation?
The frequency of OD stretching vibration of CH3OD is than that of OH in CH3OH. (Greater or smaller)
The lowest energy of a harmonic oscillator is known as
What is the selection rule for first overtone in IR spectroscopy?
The C-H stretching frequency for alkane is 2900 cm−1. What will be the corresponding C-D frequency?
The term symbol for a state 2D3/2. Fine S and L.
What is predissociation?
The Raman lines on the low frequency side of the excitation frequency are called
A molecule of the formula XY2, has two IR and one Raman active bands. Whether the molecule contain centre of symmetry or not?
What are the selection rules for pure rotational Raman spectrum of linear molecules?
Section II
Q.2
Identify various symmetry elements for a planar MX4 molecule and discuss the relationship between the different axes of rotation.
07
Write down the character table for of a C2V group and discuss their classification into various reducible representations.
07
Page 2 of 2
SLR-UF-211
Q.3
Derive expression for the rotational energy of a rigid diatomic molecule and draw the diagram for the allowed rotational energies.
07
Derive expression for the Jmax for a rigid diatomic rotator. If the rotational constant of CO is 3.8626 cm−1 calculate the value of Jmax at 300K.
(h=6.626×10−34 Js,k=1.381×10−23 JK−1,c=3.0×108 ms−1)
07
Q.4
Obtain expressions for fundamental, first and second overtone absorption frequencies of a diatomic molecule considering it as an unharmonic oscillator.
07
The first line of the P branch of IR spectrum of HCI is observed at 2864.77 cm−1. If its rotational constant is 10.61 cm−1 calculate the frequency of the fundamental band.
07
Section III
Q.5
Describe in detail the instrumentation of a Raman spectrometer.
05
Why anti-stokes lines are less intense than stokes lines?
05
Irradiation of carbon tetrachloride by a radiation of wavelength 4358 A gives lines at 4400,4419 and 4447 A. Calculate the Raman shift for these lines.
04
Q.6
Give an account of electronic spectrum of hydrogen molecule with various transitions and specify selection rules.
05
Explain the terms progression and sequences.
05
Find the quantum numbers for the states represented by 3P2, 3P1 and 3P0.
04
Q.7
Write notes on any three
14
Orthogonality theorem
Classification of molecules based on their moment of inertia
Mutual exclusion principle
Birje Sponer extrapolation