Chem-DSE-17: Molecular Spectroscopy and Structural Analysis — DU B. Sc. Life Science (Chemistry) Previous Year Question Papers

1. (a) Calculate the number of translational, rotational and vibrational degrees of freedom for (b) The [H35Cl molecule shows pure rotational lines at the following frequencies (cm-I) 20.7, 41.5, 62.0, 83.0,103.8. Calculate the bond distance of HC1. (c) Draw the different modes of vibration in the following two polyatomic molecules : water and carbon dioxide. (5,5,5) 2. (a) What is the effect on the microwave spectrum of (b) Arrange the following groups in increasing order of their absorption frequencies : Give justification (c) The force constant for [H]9F is 966 Nm-I. (i) The zero-po_int vibrational energy of this molecule when it follows harmonic motion. (ii) The frequency of the electromagnetic radiation to excite this molecule from the ground state to the first excited state. 3. (a) What is Raman effect? Explain the origin of stokes and Anti-Stokes line. (b) A molecule XY2 has the following IR and vibrational Raman spectral data : 1243 Inactive Active 2920 Active (PR) Inactive 786 Active (PQR) Inactive Giving proper explanation, arrive at the geometry of the molecule. Assign the wave numbers to specific vibrations. (c) What is TMS? Why is it used as a standard in NMR spectroscopy? (5,5,5) 4. (a) What is the selection rule for Raman rotational spectrum of diatomic molecules? Show that the Raman lines will appear at wavenumbers given by where u-o is trie wavenumber corresponding to the Rayleigh line. (b) What is the difference between spin-spin relaxation and spin-lattice relaxation? (c) Calculate the precessional frequency of a proton in a magnetic field of strength of 2.349 T. 5. (a) Given that the spin quantum numbers of[2C6, ]H[, and 2D[ are zero, half, and one, respectively, how many different energy states do these nuclei have in a magnetic field? Which of these atoms will show peak in the NMR spectra? (b) What are the fundamental requirement for a molecule to show : (iii) Raman and (iv) NMR spectra (c) The fundamental and the first overtone transitions of HBr are centered at 2560 and 5028 cm-1 respectively. Calculate the anharmonicity constant and the force constant of HBr. (5,5,5) 6. Write short notes on any three of the following : (a) Scanning Electron Microscope (b) Overtones and Combination Bands (c) Chemical shift in NMR spectroscopy (d) Intensity of spectral lines/bands (5,5,5) & Structural Analysis Answer four questions in all. Physical Constants Planck's constant 6.626x 10-3J Js Velocity of.light 3 x 108 mls Atomic mass unit 1.661 x 10-27kg Avagadro's number 6`023 x lor3 moll Mass Of electron 9.109 x I o.31 kg