Raman spectroscopy and comparison with IR, overtones and mutual exclusion principle - One Line Questions

1. Which of the following is NOT a requirement for IR activity? — A change in polarizability during the vibration.
2. Which of the following is NOT a requirement for Raman activity? — A change in dipole moment during the vibration.
3. The principle of 'mutual exclusion' implies that for centrosymmetric molecules: — A vibration cannot be both IR and Raman active.
4. For a molecule with D3h symmetry (like BF3), which vibrational modes are Raman active and IR inactive? — A1' and E' modes
5. For a molecule with D3h symmetry (like BF3), which vibrational modes are IR active and Raman inactive? — A2'' and E' modes
6. In Raman spectroscopy, what is observed when incident light interacts with a molecule? — Scattering of light with energy gain or loss (Raman scattering)
7. What fundamental principle of quantum mechanics underlies Raman spectroscopy? — Scattering of photons with a change in vibrational energy
8. Consider the molecule CO2. Its vibrational modes are: — Some are IR active and others are Raman active.
9. A molecule that is not centrosymmetric (lacks a center of inversion) will exhibit: — Partial overlap of IR and Raman active modes.
10. For a vibrational mode to be Raman active, what property of the molecule must change during the vibration? — Polarizability
11. The selection rule for Raman activity is based on the change in: — Polarizability
12. Overtones in Raman spectroscopy refer to transitions involving: — Transitions to higher vibrational energy levels (e.g., v=0 to v=2, v=0 to v=3)
13. Which of the following molecules would likely exhibit strong Raman scattering but weak IR absorption for its stretching vibrations? — N2
14. Which type of molecule is most likely to have all its vibrational modes Raman active and IR inactive? — N2
15. Overtones and combination bands are generally observed in Raman spectra at: — Lower intensity than fundamental bands.
16. What is the 'mutual exclusion principle' in vibrational spectroscopy? — If a molecule has a center of symmetry, no vibrational mode can be simultaneously IR and Raman active.
17. What is a potential issue when using very high-intensity lasers in Raman spectroscopy? — Increased chance of fluorescence, which can obscure the Raman signal.
18. Which technique is more sensitive to symmetric stretching vibrations? — Raman spectroscopy
19. For a molecule like CO2 (O=C=O), which has a center of symmetry, the symmetric stretching vibration (C-O bond lengths change equally) is: — Raman active and IR inactive
20. For a molecule like CO2 (O=C=O), which has a center of symmetry, the asymmetric stretching vibration (one C-O bond stretches while the other compresses) is: — IR active and Raman inactive
21. The bending vibration of CO2 is: — IR active and Raman inactive
22. When comparing Raman and IR spectroscopy, which statement is generally true regarding sample handling? — IR spectroscopy requires samples to be in non-polar solvents, while Raman can use polar solvents.
23. Which type of molecule typically exhibits the mutual exclusion principle? — Molecules with a center of inversion (centrosymmetric molecules)
24. Overtones in Raman spectra are typically: — Less intense than fundamental transitions
25. Which type of molecule is most likely to have all its vibrational modes IR active and Raman inactive? — N2
26. Which of the following molecules would likely exhibit strong IR absorption but weak Raman scattering for its stretching vibrations? — CO2
27. In the context of the mutual exclusion principle, a molecule with a center of symmetry will have: — Modes that are exclusively IR or exclusively Raman active.
28. For a vibrational mode to be IR active, what property of the molecule must change during the vibration? — Dipole moment
29. The selection rule for IR activity is based on the change in: — Dipole moment
30. Which technique is more sensitive to asymmetric stretching vibrations that involve a significant dipole change? — Infrared (IR) spectroscopy
31. What is the primary advantage of using Raman spectroscopy over IR spectroscopy for certain samples? — Raman spectroscopy can analyze aqueous solutions more easily.
32. What is the primary difference in the information obtained from Raman spectroscopy compared to Infrared (IR) spectroscopy? — Raman spectroscopy probes vibrational transitions based on polarizability changes, while IR probes vibrational transitions based on dipole moment changes.
33. What is the term for the scattering of light in Raman spectroscopy where the scattered photon has lower energy than the incident photon? — Stokes scattering
34. What is the term for the scattering of light in Raman spectroscopy where the scattered photon has higher energy than the incident photon? — Anti-Stokes scattering
35. What is the relationship between Stokes and Anti-Stokes scattering in Raman spectroscopy at thermal equilibrium? — Stokes scattering is more intense than Anti-Stokes scattering.
36. If a vibrational mode is IR inactive, it means: — The dipole moment does not change during the vibration.
37. Why are overtones weaker than fundamental transitions in Raman spectroscopy? — The change in polarizability is smaller for higher energy transitions.
38. The 'selection rule' for a spectroscopic technique dictates: — The transitions that are allowed or forbidden.
39. The frequency of Raman scattered light is related to: — The frequency of the incident light and the vibrational frequencies of the molecule.
40. The study of overtones in Raman spectroscopy can provide information about: — The anharmonicity of molecular vibrations.
41. What is the energetic basis for Anti-Stokes scattering? — The molecule gains energy from the incident photon, transitioning from a higher vibrational state to a lower one.
42. The intensity of Anti-Stokes scattering in Raman spectroscopy is dependent on: — The number of molecules in excited vibrational states.
43. If a vibrational mode is Raman inactive, it means: — The polarizability does not change during the vibration.
44. The intensity of Raman scattering is generally proportional to: — The intensity of the incident light and the polarizability derivative.
45. The intensity of IR absorption is generally proportional to: — The intensity of the incident IR radiation and the dipole moment derivative.
46. What is the approximate frequency shift observed in Raman scattering? — Typically in the infrared region
47. Which of the following is a characteristic of Raman spectroscopy instrumentation? — Uses a monochromatic light source (laser)
48. The term 'fundamental transition' in vibrational spectroscopy refers to: — v=0 to v=1
49. Why can Raman spectroscopy be advantageous for analyzing samples in aqueous solutions? — Water has very weak Raman scattering compared to many solutes.
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