UV Luminance Spectroscopy

Q1: 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

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

No answer description is available.

Q2: 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

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

No answer description is available.

Q3: Internal conversion is where

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 none of the above

ANS:C - A molecule converts excess electronic energy to vibrational energy

No answer description is available.

Q4: 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

ANS:A - Because the magnitude of the output signal is proportional to the power of the incident radiation

No answer description is available.

Q5: Fluorescence occurs when

A a molecule returns to the electronic ground state from an excited triplet state by losing it's excess energy as a photon

B a molecule returns to the electronic ground state from an excited singlet state by losing it's excess energy as a photon

C a molecule lowers its vibrational energy by losing it's excess energy as a photon

D none of the above

ANS:B - a molecule returns to the electronic ground state from an excited singlet state by losing it's excess energy as a photon

No answer description is available.

Q6: 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

ANS:C - To compensate for power fluctuations in the radiation source

No answer description is available.

Q7: Why phosphorescence measurements are usually made at a low temperature?

A To prevent thermal degradation of the phosphorescent species

B To promote phosphorescence by slowing the rate of radiationless transfer processes

C To increase the efficiency of the detector

D To decease the efficiency of detector

ANS:B - To promote phosphorescence by slowing the rate of radiationless transfer processes

No answer description is available.

Q8: What is the relationship between wavelength and wave number?

A Wavenumber = 1 / wavelength in centimeters

B Wavenumber - wavelength in nanometers = 1

C Wavelength in nanometers x wavenumber = 1

D None of the above

ANS:A - Wavenumber = 1 / wavelength in centimeters

No answer description is available.



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