Spectroscopy Fundamentals Quiz
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Questions and Answers

What happens when a molecule absorbs UV-vis light?

  • The molecule becomes pyramidal in both S1 and T1 excited states.
  • The molecule emits a photon.
  • An electron is promoted to a higher energy molecular orbital. (correct)
  • The molecule undergoes internal conversion.

    • What determines the type of electronic transition in a molecule?

  • The molecule's color.
  • The molecule's density.
  • The molecule's size.
  • The molecule's functional groups. (correct)

    • What is the lowest energy electronic transition of formaldehyde?

  • From sigma to sigma*
  • From n to sigma*
  • From n to pi* (correct)
  • From pi to pi*

    • What is the purpose of infrared and microwave radiation in spectroscopy?

    <p>To change the vibrational motion of a molecule.</p> Signup and view all the answers

    What are the two types of relaxation processes from an excited state?

    <p>Vibrational and electronic relaxation.</p> Signup and view all the answers

    What is the difference between fluorescence and phosphorescence?

    <p>Fluorescence involves emission of a photon, while phosphorescence involves conversion of light to heat.</p> Signup and view all the answers

    What is the molecular orbital diagram for formaldehyde?

    <p>Four occupied orbitals, including a nonbonding orbital (n) and a pi antibonding orbital (π*).</p> Signup and view all the answers

    What are the factors that affect the relative rates of relaxation?

    <p>The molecule's solvent and temperature.</p> Signup and view all the answers

    What is the purpose of vibrational and rotational states in spectroscopy?

    <p>To identify the molecule and its electronic state.</p> Signup and view all the answers

    What is the difference between fluorescence and phosphorescence lifetimes?

    <p>Fluorescence has a longer lifetime than phosphorescence.</p> Signup and view all the answers

    What is the purpose of internal conversion in spectroscopy?

    <p>To convert light into heat.</p> Signup and view all the answers

    What happens to formaldehyde in its excited states?

    <p>It becomes pyramidal.</p> Signup and view all the answers

    What happens when a molecule absorbs UV-vis light?

    <p>An electron is promoted to a higher energy molecular orbital.</p> Signup and view all the answers

    What determines the type of electronic transition in a molecule?

    <p>The molecule's functional groups.</p> Signup and view all the answers

    What is the lowest energy electronic transition of formaldehyde?

    <p>From n to pi*</p> Signup and view all the answers

    What is the purpose of infrared and microwave radiation in spectroscopy?

    <p>To change the vibrational motion of a molecule.</p> Signup and view all the answers

    What are the two types of relaxation processes from an excited state?

    <p>Vibrational and electronic relaxation.</p> Signup and view all the answers

    What is the difference between fluorescence and phosphorescence?

    <p>Fluorescence involves emission of a photon, while phosphorescence involves conversion of light to heat.</p> Signup and view all the answers

    What is the molecular orbital diagram for formaldehyde?

    <p>Four occupied orbitals, including a nonbonding orbital (n) and a pi antibonding orbital (π*).</p> Signup and view all the answers

    What are the factors that affect the relative rates of relaxation?

    <p>The molecule's solvent and temperature.</p> Signup and view all the answers

    What is the purpose of vibrational and rotational states in spectroscopy?

    <p>To identify the molecule and its electronic state.</p> Signup and view all the answers

    What is the difference between fluorescence and phosphorescence lifetimes?

    <p>Fluorescence has a longer lifetime than phosphorescence.</p> Signup and view all the answers

    What is the purpose of internal conversion in spectroscopy?

    <p>To convert light into heat.</p> Signup and view all the answers

    What happens to formaldehyde in its excited states?

    <p>It becomes pyramidal.</p> Signup and view all the answers

    What happens when a molecule absorbs UV-vis light?

    <p>An electron is promoted to a higher energy molecular orbital</p> Signup and view all the answers

    What determines the type of electronic transition a molecule undergoes?

    <p>The molecule's shape</p> Signup and view all the answers

    What happens to formaldehyde's shape when it is in the S1 and T1 excited states?

    <p>It becomes pyramidal</p> Signup and view all the answers

    How many occupied orbitals does the molecular orbital (MO) diagram for formaldehyde show?

    <p>Four</p> Signup and view all the answers

    What is the lowest energy electronic transition of formaldehyde?

    <p>From n to pi*</p> Signup and view all the answers

    What types of motion can infrared and microwave radiation change in a molecule?

    <p>All of the above</p> Signup and view all the answers

    What are associated with each electronic state of a molecule?

    <p>Vibrational and rotational states</p> Signup and view all the answers

    What are the types of relaxation processes from an excited state?

    <p>All of the above</p> Signup and view all the answers

    What happens to a molecule after it absorbs light?

    <p>It undergoes internal conversion, intersystem crossing, and fluorescence</p> Signup and view all the answers

    What does internal conversion convert light into?

    <p>Heat</p> Signup and view all the answers

    What determines the relative rates of relaxation from an excited state?

    <p>The solvent's temperature and pressure</p> Signup and view all the answers

    What is the difference between fluorescence and phosphorescence in terms of lifetime?

    <p>Phosphorescence has a longer lifetime</p> Signup and view all the answers

    Study Notes

    Fundamentals of Spectroscopy: What Happens When a Molecule Absorbs Light?

    • Absorption of UV-vis light promotes an electron to a higher energy molecular orbital.
    • Different types of electronic transitions require different functional groups.
    • Formaldehyde in its ground state is planar, but becomes pyramidal in both S1 and T1 excited states.
    • The molecular orbital (MO) diagram for formaldehyde shows four occupied orbitals, including a nonbonding orbital (n) and a pi antibonding orbital (π*).
    • The lowest energy electronic transition of formaldehyde is from n to pi*.
    • Infrared and microwave radiation can change vibrational, translational, and rotational motion of a molecule.
    • Vibrational and rotational states are associated with each electronic state, and transitions between different states can occur.
    • Relaxation processes from excited state include vibrational and rotational relaxation through collision with solvent or other molecules, and electronic relaxation through the release of a photon.
    • After absorption, a molecule can undergo internal conversion, intersystem crossing, fluorescence, or phosphorescence.
    • Internal conversion converts light into heat, while fluorescence and phosphorescence involve emission of a photon.
    • The relative rates of relaxation depend on the molecule, solvent, temperature, and pressure.
    • Fluorescence has a short lifetime (10-8 to 10-4 s), while phosphorescence has a longer lifetime (10-4 to 102 s).

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    Chapter 17b Fundamentals of Spectroscopy PDF

    Description

    Test your knowledge on the fundamentals of spectroscopy and learn what happens when a molecule absorbs light. This quiz delves into the different types of electronic transitions, vibrational and rotational motion, and relaxation processes from excited states. Discover the various ways a molecule can emit light, and the factors that affect the rates of relaxation. If you're fascinated by the science of light and molecules, this quiz is for you.

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