Atomic and Molecular Physics — DU B.Sc. (Hons) Physics Previous Year Question Papers

D Medium of setting the Question paper: English Language g) Question paper set number: I (a) Write a short note on paranagnetic molecular orbitals and fractional bond order using the 02 molecule as an example. a) Discuss the difference between a (sigma) and " ®i) molecular orbitals with suitable diagrams. (c) Explain whether the ground state level 2Sz¢ can exhibit Zeeman splitting in a weak magnetic field. (d) State the Born-Oppenheimer approximation and briefly explain its significance in molecular spectros copy. (e) Distinguish between Stokes and anti-Stokes lines observed in Ranan scattering. (I) Briefly discuss the physical conditions necessary for a linear combination of atomic orbitals a,CAO) to fom stable molecular orbitals. (#=J) of a hydrogen atom. 2. (a) Describe the anomalous Zeeman effect. Derive the expression for the energy shift of an atomic state in a weak extemal magnetic field and trace the splitting transitions for the Sodium Dz line. (10 Marks) @)InaStem-Gerlachexperiment,abeamofsilveratoms/4=J4BJpassesthroughanon-unifom magnetic field gradient of 1.5 x 103 T/in over a length of 4 cm. Calculate the transverse deflection of the two split beams on a screen placed at the edge of the magnetic field. (5 Marks) (c) Explain why homonuclear diatomic molecular orbitals do not possess a permanent electric dipole moment and discuss how this affects their pure rotational spectra. (3 Marks) 3. (a) State and explain the Franck-Condom principle. Discuss its quantum mechanical interpretationregardingtheintensitydistributioninelectronic-vibrationaltransitionsusing potential energy curves. (10 Marks) a)Discussthedifferencebetweenradiativerelaxatibn(fluorescence/phosphorescence)and non-radiative relaxation of an excited molecular state. (5 Marks) (c) What is zero-point energy? If the fundamental .vibrational wave number Of an JIG/ molecule is 2886 czre-', determine its zero-point energy in Joules. (3 Marks) 4. (a) CQmpare Infrared (R) spectroscopy and Raman spectroscopy. Discuss their selection rules, the respective electromagnetic energy regions utilized and their complementary nature in structural analysis. (10 Marks) a) The ground state electronic configuration of Carbon is Js22rf2p2. Find all the possible standard spectroscopic term symbols for this equivalent electron configuration using L-S coupling. (5 Marks) (c) Define the Paschen-Back effect and discuss its importance when an atom is placed in a very strong magnetic field. (3 Marks) 5. (a) What is meant by the fine structure of alkali spectra? How is it explained based on spin-orbit interaction, and explain why the screening constant causes alkali levels to be deeper than corresponding hydrogen levels? (10 Marks) a) Explain the isotope effect in vibrational spectroscopy. Show how the vibrational frequency shifts when an atom in a diatomic molec'ule is substituted by its heavier isotope. (c) Write a short note on the physical mechanisms behind the production of Continuous and