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