UV Luminance Spectroscopy – Section 1

1. What is the relationship between wavelength and wavenumber?

A. Wavenumber = 1 / wavelength in centimeters
B. Wavenumber – wavelength in nanometers = 1
C. Wavelength in nanometers x wavenumber = 1
D. None of the above

Correct Answer: A. Wavenumber = 1 / wavelength in centimeters

2. In the intersystem crossing

A. the spin of an excited electron reverses, changing the state of the molecule (from singlet state to triplet state or vice versa)
B. a molecule converts its excess energy to light and emits a photon
C. a molecule converts excess electronic energy to vibrational energy
D. all of the above

Correct Answer: A. the spin of an excited electron reverses, changing the state of the molecule (from singlet state to triplet state or vice versa)

3. Why must the radiation source for fluorescence spectrometry be more powerful than for absorption spectroscopy?

A. Because the magnitude of the output signal is proportional to the power of the incident radiation
B. Because the sample won’t fluoresce if the incident radiation is of low power
C. To allow for scattering by the sample
D. None of the above

Correct Answer: A. Because the magnitude of the output signal is proportional to the power of the incident radiation

4. Why do fluorescence spectrometers often use double-beam optics?

A. So a reference solution can be used
B. To compensate for beam attenuation by the monochromator
C. To compensate for power fluctuations in the radiation source
D. All of the above

Correct Answer: C. To compensate for power fluctuations in the radiation source

5. For a molecule to absorb IR, why must the molecule’s vibrations cause fluctuations in the dipole moment of the molecule?

A. Because a change in dipole moment lowers the energy required for electronic transitions
B. Because for absorption to occur, the radiation must interact with the electric field caused by changing dipole moment
C. Because fluctuations in the dipole moment allow the molecule to deform by bending and stretching
D. All of the above

Correct Answer: B. Because for absorption to occur, the radiation must interact with the electric field caused by changing dipole moment

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