Applications of Spectroscopy

1 : 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
Answer : c

2 : 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
Answer : b

3 : 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
Answer : b

4 : 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
Answer : a

5 : 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
Answer : a

6 : 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
Answer : a

7 : 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
Answer : c

8 : 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
Answer : b

9. If the absorption of electromagnetic radiation by matter results in the emission of radiation of the same or longer wavelengths for a long or a short time, the phenomenon is termed as which of the following?
a) Luminescence
b) Fluorescence
c) Phosphorescence
d) Spontaneous emission
Answer: a
Explanation: If the absorption of electromagnetic radiation by matter results in the emission of radiation of the same or longer wavelengths for a short or a long time, the phenomenon is termed as luminescence. Usually, absorption of electromagnetic radiation results in the emission of radiation.

10. If the absorption of electromagnetic radiation by matter results in the emission of radiation of the same or longer wavelengths for a short time, the phenomenon is termed as which of the following?
a) Luminescence
b) Fluorescence
c) Phosphorescence
d) Spontaneous emission
Answer: b
Explanation: If the absorption of electromagnetic radiation by matter results in the emission of radiation of the same or longer wavelengths for a short time, the phenomenon is termed as fluorescence. Fluorescence emissions are characteristic of the particular element.

11. If the absorption of electromagnetic radiation by matter results in the emission of radiation of the same or longer wavelengths for a long time, the phenomenon is termed as which of the following?
a) Luminescence
b) Fluorescence
c) Phosphorescence
d) Spontaneous emission
Answer: c
Explanation: If the absorption of electromagnetic radiation by matter results in the emission of radiation of the same or longer wavelengths for a long time, the phenomenon is termed as phosphorescence. Phosphorescence is a type of luminescence.

12. Prompt emission of X-ray by an atom ionised by a higher energy X-ray is a type of which of the following phenomena?
a) Luminescence
b) Fluorescence
c) Phosphorescence
d) Spontaneous emission
Answer: b
Explanation: Prompt emission of X-ray by an atom ionised by a higher energy X-ray is a type of fluorescence. Fluorescence emissions are characteristic of the particular element.

13. The measurement of intensity of fluorescent X-rays provide a simple and ____________ way of _____________ analysis.
a) Destructive, quantitative
b) Non-destructive, quantitative
c) Destructive, qualitative
d) Non-destructive, qualitative
Answer: b
Explanation: The measurement of an intensity of fluorescent X-rays provide a simple and non-destructive way of quantitative analysis.

14. The energy of the emitted X-rays depends upon the _________ of the atom and their intensity depends upon the __________
a) Atomic number, amount of sample
b) Mass number, amount of sample
c) Mass number, concentration of atoms
d) Atomic number, concentration of atoms
Answer: d
Explanation: The energy of the emitted X-rays depends upon the atomic number of the atom and their intensity depends upon the concentration of atoms in the sample. X-ray fluorescence spectroscopy is based on this principle.

15. Which of the following is Mosely’s equation if ‘C’ is the speed of light, ‘a’ is proportionality constant, ‘σ’ is a constant which depends on electronic transition series, ‘Z’ is the atomic number and ‘λ’ is the wavelength?
a) Cλ= a(Z-σ)2
b) C/λ= a(Z-σ)2
c) C(Z-σ)2= aλ
d) C(Z-σ)2= a/λ

16. The problem of spectral interference is not severe in X-ray spectroscopy.
a) True
b) False
Answer: a
Explanation: The problem of spectral interference is not severe in X-ray spectroscopy. This is due to the relative simplicity of the X-ray spectra.

17. In X-ray fluorescence spectrometer, the relationship between the excitation intensity and the intensity of fluorescence does not depend on which of the following?
a) Spectrum of the incident radiation
b) Angle of radiance
c) Molecular weight
d) Incident angle
Answer: d
Explanation: In X-ray fluorescence spectrometer, the relationship between the excitation intensity and the intensity of fluorescence does not depend on the incident angle. It depends on the absorption of path length.

18. Fluorescent X-ray spectrometers would require only moderate-intensity X-ray tubes.
a) True
b) False
Answer: b
Explanation: Fluorescent X-ray spectrometers would require high-intensity X-ray tubes. They also require sensitive detectors and suitable X-ray optics.

19. The fact that the fluorescence wavelength is often much longer than the irradiation wavelength (Stokes shift) is a consequence of which phenomenon?
a) low extinction coefficients (Lambert-Beer law)
b) vertical transitions (Kasha’s rule)
c) high ISC rates (El Sayed rule)
d) the Franck–Condon principle
Answer: d
Explanation: The reason why Stokes shifts occur is the Franck–Condon principle, which states that a change in the electronic state of some molecule caused by the absorption of a photon occurs so rapidly that the motion of the nuclear coordinates during the transition can be neglected. After the electronic transition is complete, the molecule’s nuclear coordinates then relax into a lower-energy configuration in response to the change in the electronic wave function.

20. Which of the following is an incorrect statement?
a) First step in photochemistry is excited state (photoexcitation)
b) Photochemical reactions are caused by absorption of ultraviolet only
c) When a molecule or atom in the ground state (S0) absorbs light, one electron is excited to a higher orbital level
d) It is possible for the excited state S1 to undergo spin inversion
Answer: b
Explanation: Photochemical reactions are caused by absorption of ultraviolet, (wavelength from 100 to 400 nm), visible light (400 – 750 nm) or infrared radiation (750 – 2500 nm).

21. Which regions of the light radiations of the visible ultraviolet lying between – wavelength are chiefly concerned in bringing about photochemical reactions?
a) 1000 Å and 2000 Å
b) 1500 Å and 1000 Å
c) 8000 Å and 2000 Å
d) 19000 Å and 12,000 Å
Answer: c
Explanation: The region of interest for photochemistry is between 8000 Å and 2000 Å of visible and ultraviolet (UV), are only a small part of the full electromagnetic spectrum. Longer wavelengths, e.g., far infrared, tend to cause the vibrational excitation of molecules, which results in heating. Shorter wavelength X-rays cause ionization.

22. Which of the following instruments is used to measure the energy of the monochromatic radiation most accurately?
a) Photoelectric cell
b) Thermopile
c) The potential detector
d) The chemical actinometer
Answer: b
Explanation: A thermopile is an electronic device that converts thermal energy into electrical energy. It is composed of several thermocouples connected usually in series or, less commonly, in parallel.

23. The molar extinction coefficient of B (MW = 180) is 4 x 103 L mol-1 cm-1. One-liter solution of C which contains 0.1358 g pharmaceutical preparation of B, shows an absorbance of 0.411 in a 1 cm quartz cell. What is the percentage (w/w) of B in the pharmaceutical preparation?
a) 10.20
b) 13.60
c) 20.40
d) 29.12
Answer: b
Explanation:

24. What are the appropriate reasons for the deviation from the Beer’s law among the following?
(A) Monochromaticity of light
(B) Very high concentration of analyte
(C) Association of analyte
(D) Dissociation of analyte
a) A, B and D
b) B, C and D
c) A, C and D
d) A, B and C
Answer: b
Explanation: Reasons for derivation from Beer’s law are very high concentration of analyte, Association or Dissociation of analyte and Refractive index → Polychromatic light. Monochromaticity of light don’t have any effect on Beer’s law.

25. Which of the following will result in deviation from Beer’s law?
(A) Change in a refractive index of medium
(B) Dissociation of analyte on dilution
(C) Polychromatic light
(D) Path length of cuvette
a) A, B and C
b) B, C and D
c) A, C and D
d) A, B and D
Answer: a
Explanation: Change in a refractive index of medium, Dissociation of analyte on dilution and Polychromatic light (reflective index) will result in deviation from Beer’s law.

26. The quantum efficiency of a photochemical reaction is defined as _______
a) ratio of molecules decomposed in a given time to the number of quanta absorbed in the same time
b) number of 11101ecules decomposed in a given time
c) number or quanta absorbed percent time
d) ratio of’ molecules decomposed in a given time to the number of quanta emitted in the same time
Answer: a
Explanation: According to the definition ratio of molecules decomposed in a given time to the number of quanta absorbed at the same time is the correct option.

27. Which of the following are the reactions in which molecules absorbing light do not themselves react but induce other molecules to react?
a) Free radical reactions
b) Chain reactions
c) Reversible reactions
d) Photosensitized reactions
Answer: d
Explanation: Photosensitized reactions is the reactions in which molecules absorbing light do not themselves react but induce other molecules to react.