Uv Luminance Spectroscopy(Biochemistry ) Questions and Answers

Question 1.  
What is the relationship between wavelength and wave number?
  1.    Wavenumber = 1 / wavelength in centimeters
  2.    Wavenumber - wavelength in nanometers = 1
  3.    Wavelength in nanometers x wavenumber = 1
  4.    None of the above
Explanation:-
Answer: Option A. -> Wavenumber = 1 / wavelength in centimeters
Question 2.  Why do fluorescence spectrometers often use double-beam optics?
  1.    So a reference solution can be used
  2.    To compensate for beam attenuation by the monochromator
  3.    To compensate for power fluctuations in the radiation source
  4.    All of the above
Explanation:-
Answer: Option C. -> To compensate for power fluctuations in the radiation source
Question 3.  In the intersystem crossing
  1.    the spin of an excited electron reverses, changing the state of the molecule (from singlet state to triplet state or vice versa)
  2.    a molecule converts its excess energy to light, and emits a photon
  3.    a molecule converts excess electronic energy to vibrational energy
  4.    all of the above
Explanation:-
Answer: Option A. -> the spin of an excited electron reverses, changing the state of the molecule (from singlet state to triplet state or vice versa)
Question 4.  Internal conversion is where
  1.    the spin of an excited electron reverses, changing the state of the molecule (from singlet state to triplet state or vice versa)
  2.    A molecule converts its excess energy to light, and emits a photon
  3.    A molecule converts excess electronic energy to vibrational energy
  4.    none of the above
Explanation:-
Answer: Option C. -> A molecule converts excess electronic energy to vibrational energy
Question 5.  
For a molecule to absorb IR, why must the molecule's vibrations cause fluctuations in the dipole moment of the molecule?
  1.    Because a change in dipole moment lowers the energy required for electronic transitions
  2.    Because for absorption to occur, the radiation must interact with the electric field caused by changing dipole moment
  3.    Because fluctuations in the dipole moment allow the molecule to deform by bending and stretching
  4.    All of the above
Explanation:-
Answer: Option B. -> Because for absorption to occur, the radiation must interact with the electric field caused by changing dipole moment
Question 6.  Why must the radiation source for fluorescence spectrometry be more powerful than for absorption spectroscopy?
  1.    Because the magnitude of the output signal is proportional to the power of the incident radiation
  2.    Because the sample won't fluoresce if the incident radiation is of low power
  3.    To allow for scattering by the sample
  4.    None of the above
Explanation:-
Answer: Option A. -> Because the magnitude of the output signal is proportional to the power of the incident radiation
Question 7.  Why phosphorescence measurements are usually made at a low temperature?
  1.    To prevent thermal degradation of the phosphorescent species
  2.    To promote phosphorescence by slowing the rate of radiationless transfer processes
  3.    To increase the efficiency of the detector
  4.    To decease the efficiency of detector
Explanation:-
Answer: Option B. -> To promote phosphorescence by slowing the rate of radiationless transfer processes
Question 8.  Fluorescence occurs when
  1.    a molecule returns to the electronic ground state from an excited triplet state by losing it's excess energy as a photon
  2.    a molecule returns to the electronic ground state from an excited singlet state by losing it's excess energy as a photon
  3.    a molecule lowers its vibrational energy by losing it's excess energy as a photon
  4.    none of the above
Explanation:-
Answer: Option B. -> a molecule returns to the electronic ground state from an excited singlet state by losing it's excess energy as a photon
Question 9. . Fluorescence occurs when
  1.    a molecule returns to the electronic ground state from an excited triplet state by losing it's excess energy as a photon
  2.    a molecule returns to the electronic ground state from an excited singlet state by losing it's excess energy as a photon
  3.    a molecule lowers its vibrational energy by losing it's excess energy as a photon
  4.    none of the above
Explanation:-
Answer: Option B. -> a molecule returns to the electronic ground state from an excited singlet state by losing it's excess energy as a photon
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