Instrumental Analysis: Molecular Fluorescence Spectroscopy
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Questions and Answers

What is the process called when an electron relaxes from a higher electronic state to a lower electronic state by emitting heat?

  • Internal Conversion (correct)
  • Vibrational Relaxation
  • Radiational Deactivation
  • External Conversion

    • What is the emission of a photon when an electron relaxes from the S1 → S0 state known as?

  • Bioluminescence
  • Fluorescence (correct)
  • Phosphorescence
  • Chemiluminescence

    • Which of the following is NOT a way to stabilize the excited singlet state?

  • Working at high concentration of solute (correct)
  • Working with high viscosity solvents
  • Working at low temperature
  • Working at low pressure

    • What is the process of emitting radiation classified into?

    <p>Fluorescence and phosphorescence</p> Signup and view all the answers

    What is the process called when molecules in electronically excited states pass to a lower electronic state by colliding with other molecules?

    <p>External Conversion</p> Signup and view all the answers

    What is the result of radiationless deactivation?

    <p>Emission of heat</p> Signup and view all the answers

    What is the energy level associated with the transition of π-π*?

    <p>S2</p> Signup and view all the answers

    What is the characteristic of singlet state?

    <p>Paired electrons with no net magnetic moment</p> Signup and view all the answers

    Why do molecules with relatively unstable excited states return to the ground state by radiationless collision deactivation?

    <p>Because they have unstable excited states</p> Signup and view all the answers

    What is the characteristic of triplet state?

    <p>Unpaired electrons with magnetic moment</p> Signup and view all the answers

    What is the comparative energy level of the excited triplet state versus the corresponding excited singlet state?

    <p>Lower energy level</p> Signup and view all the answers

    Which type of molecules are diamagnetic?

    <p>Molecules with paired electrons</p> Signup and view all the answers

    Which of the following compounds favors phosphorescence over fluorescence?

    <p>Heterocyclic compounds</p> Signup and view all the answers

    What is the effect of increased temperature on fluorescence and phosphorescence?

    <p>It decreases fluorescence and phosphorescence</p> Signup and view all the answers

    Why do solvents containing heavy atoms decrease fluorescence?

    <p>They enhance intersystem crossing</p> Signup and view all the answers

    What is the effect of dissolved oxygen on fluorescence and phosphorescence?

    <p>It decreases fluorescence and increases phosphorescence</p> Signup and view all the answers

    What type of lamp is used for scanning spectra?

    <p>High-pressure xenon lamp</p> Signup and view all the answers

    What is the reason for the pH dependence of fluorescence in acidic or basic aromatic compounds?

    <p>Emission intensity and wavelength differ with pH</p> Signup and view all the answers

    What is the main reason for the emission spectrum being shifted to longer wavelength?

    <p>Lower energy of emission</p> Signup and view all the answers

    What is the quantum yield of highly fluorescent molecules?

    <p>Nearly one</p> Signup and view all the answers

    What happens to the fluorescence when the concentration of a compound becomes too large?

    <p>Linearity is lost</p> Signup and view all the answers

    What is the main reason for self-absorption of fluorescence?

    <p>Overlapping of emission and absorption peaks</p> Signup and view all the answers

    What type of molecular structure is ideal for fluorescence?

    <p>Rigid, planar, and aromatic</p> Signup and view all the answers

    What is the relationship between fluorescence and concentration when absorbance is less than 0.05?

    <p>Direct proportionality</p> Signup and view all the answers

    What is the purpose of using a double beam instrument in instrumental analysis?

    <p>To compensate for the variation of emitted radiation with wavelength</p> Signup and view all the answers

    What is the function of the wavelength selector in instrumental analysis?

    <p>To select the most intense emitted wavelength</p> Signup and view all the answers

    What type of detector is used in instrumental analysis due to the low intensity of emitted radiation?

    <p>Photomultiplier type detector</p> Signup and view all the answers

    Why is the detector placed at a right angle to the cuvette in instrumental analysis?

    <p>To prevent the transmitted light of excitation from being recorded</p> Signup and view all the answers

    For nonfluorescent substances, what is the method used to induce fluorescence?

    <p>By chemical reaction to form a fluorescent chelate</p> Signup and view all the answers

    What is the purpose of constructing a calibration curve in instrumental analysis?

    <p>To determine the concentration of an unknown sample</p> Signup and view all the answers

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