CHM401: FAST TIPS TO UNDERSTAND THEORY OF MOLECULAR SPECTROSCOPY

By | October 8, 2019

CHM 401 THEORY OF MOLECULAR SPECTROSCOPY (COURSE OUTLINE)
  • Basic principles of spectroscopy theory: Basic instrumentation and applications of microwave, infrared and Raman, nuclear magnetic resonance (NMR), electron spin resonance (ESR), electronic Mossbauer spectroscopy and some latest spectroscopic techniques

MATERIAL ONE : WHAT YOU SHOULD KNOW

PART A

FAST TIPS TO UNDERSTAND THEORY OF MOLECULAR SPECTROSCOPY

  • Describe the Raman effect
  • State the condition necessary for Raleigh scattering and show the difference between Raleigh, Stokes and anti-stokes lines.
  • State the Gross and Quantum Mechanical Selection rules for a Raman active molecule.
  • Show that a molecule could be both infrared and Raman active.
  • Explain the term polarizability
  • Using the basic postulates of infrared spectroscopy, obtain an expression describing the vibrational motion of a diatomic molecule.
  • State the quantum selection rule for the appearance of the infrared absorption band of a diatomic molecule.
  • What are the conditions necessary for this observation?
  • Write down an expression for the zero-point energy?
  • What is the implication of Zero-point energy for an anharmonic oscillator ?

  • Briefly explain molecular spectroscopy
    -Sketch a diagram of double beam UV Visible spectrophotometer
    -What is Nuclear Magnetic resonance spectroscopy
    -List with examples the factors that affect the chemical shift in NMR spectroscopy

  • Briefly explain the different types of hydrogen environment that could be known and picked by NMR spectroscopy
    -Consider the chemical shift of the following compounds
    . HC=CHnCi
    . HβHC=CHαCH=CH2
  • Explain the meaning of the following terms :
    . Broadening of spectra lines
    . Intensity of spectral transitions
    . Born-Oppenheimer approximation
  • The microwave spectrum of Hl molecule consists of a series of equidistant lines with a spacing of
    12.8 cm-1 calculate the moment of inertia and the bond distance of the HI molecule
  • Draw a well labeled diagram of a microwave spectrophotometer indicating all the components and write concise notes on the importance of each component of the instrument
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MATERIAL ONE : WHAT YOU SHOULD KNOW

PART B

FAST TIPS TO UNDERSTAND THEORY OF MOLECULAR SPECTROSCOPY

  • Give reasons why Raman spectroscopy is often described as “scattering” phenomenon.
  • What are stokes and anti-stokes lines in Raman spectrum? Why are stokes lines more intense than anti-stokes lines?
  • How many normal modes are possible in the following compounds C2H6, C6H6, H2O, HCl and CO2
  • Write a concise note on the criteria for the appearance of Raman spectral lines.
  • Define the term spectroscopy and write down expressions for the major components of the electromagnetic radiation.
  • Using the simple harmonic oscillator (SHO) and rigid rotor approximation models, deduce an expression for the possible transition energies associated with the rotation-vibration spectra of a diatomic molecule. Hence, show that the vibration-rotation spectra would consist of lines with equal spacing on either side of the band origin
  • Briefly describe the emergence of a spectrum and show how the properties of electromagnetic radiation may be likened to the physical displacement of a stretched “vibrating string”
    -Describe the “fate” of a nucleus in a static applied magnetic field HO
    -Show how the spin quantum number I is dependent on the mass and atomic number of the spinning nucleus and why do nuclei with I=0 fail to give rise to NAMR signals?
  • Obtain an expression for the frequency of the electromagnetic radiation responsible for the two nuclear energy states Mi=±1/2 for a nucleus at resonance in an NMR experiment.
    -Write concise notes on the parameters necessary for the structural elucidation studies of a diatomic molecule using Mossbauer spectroscopy.
  • Using the basic postulates of Infrared (IR) spectroscopy, obtain an expression describing the vibrational
    motion of a diatomic molecule.
  • State the quantum selection rule for the appearance of the Infrared absorption band of a diatomic molecule.
    -What are the conditions necessary for this observation?
  • Write down an expression for the zero-point energy and what is the implication of this energy for an
    anharmonic oscillator?
  • The difference in frequency between adjacent lines in the rotational spectrum of HCI is 6.33 x 1011 sec-1 Express this number in terms of a difference in
    . wavelength
    . wave number
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. The force constant in Br2 is 2.4 dyne/cm, calculate the fundamental vibration mode.
– Sketch the potential energy curve for a diatomic molecule and a rigid rotor.
-Write down an expression for the potential energy function of a simple harmonic oscillator.
– Write down the Morse equation for potential energy function of an anharmonic oscillator. Define all the terms of the equation.
Table of constants
C= 2.998 x 1010 m s-1 K= 1.380 x 10-23 JK-1h=6.626 x 10-34Js NO = 6.02 x 1023 mol-1 R= 109677.76 cm -1

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