Infrared Spectroscopy: Effect on Molecules
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Questions and Answers

What types of vibrations occur in molecules when irradiated with IR radiation?

  • Rotational and translational vibrations
  • Stretching and bending vibrations (correct)
  • Symmetric and asymmetric vibrations
  • Vibrations in the UV region

    • In which region of the spectrum does ultraviolet radiation lie?

  • High energy side of the visible spectrum (correct)
  • Low energy side of the visible spectrum
  • Far IR region
  • Between visible and infrared spectrum

    • What type of energy is largely associated with infrared radiation?

  • Mechanical energy
  • Electromagnetic energy
  • Chemical energy
  • Thermal energy (correct)

    • What property of molecules can be determined using IR spectroscopy?

    <p>Functional groups</p> Signup and view all the answers

    What law can be used to predict the oscillation frequency in molecules?

    <p>Hooke's Law</p> Signup and view all the answers

    How are IR spectra usually recorded?

    <p>Transmittance vs wave number (cm-1)</p> Signup and view all the answers

    Which factor affects the vibrational frequency of a molecule according to Hook's Law?

    <p>Force constant</p> Signup and view all the answers

    What happens to the vibrational frequency when the bond strength of a molecule increases?

    <p>Vibrational frequency increases</p> Signup and view all the answers

    Which type of molecules have changing or fluctuating dipole moments during vibration and are considered IR active?

    <p>Molecules with heteronuclear bonds</p> Signup and view all the answers

    What is the formula to calculate the total degree of freedom for a linear molecule?

    <p>3N - 5</p> Signup and view all the answers

    Which type of molecules are considered IR inactive due to having no dipole moment?

    <p>Homonuclear molecules</p> Signup and view all the answers

    What is the essential condition for a molecule to be IR active according to the provided text?

    <p>Changing or fluctuating dipole moment during vibration</p> Signup and view all the answers

    Why do IR spectra appear upside down and right to left?

    <p>Because of the nature of IR radiation absorption</p> Signup and view all the answers

    What is the essential condition for a molecule to be IR-active?

    <p>Possessing a fluctuating dipole moment during vibration</p> Signup and view all the answers

    How many total degrees of freedom does a molecule with N atoms have?

    <p>$3N$</p> Signup and view all the answers

    Why are homonuclear diatomic molecules not IR-active?

    <p>They do not have a fluctuating dipole moment</p> Signup and view all the answers

    What kind of vibrations give rise to absorption in the IR region?

    <p>Vibrations that cause a fluctuating dipole moment</p> Signup and view all the answers

    Why do fewer bands appear in the IR spectra than theoretically possible?

    <p>Because certain vibrations are not observed</p> Signup and view all the answers

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