Test on Molecular Spectroscopy: Fundamentals and Applications

Question 1: The general strategy of molecular spectroscopy primarily starts by inferring chemical knowledge directly from observed spectra.

A. Ano

B. Ne

Explanation: The general strategy of molecular spectroscopy begins with constructing a physical model and determining possible energy levels. Inferring chemical knowledge is a later step after investigating the interaction with photons and inferring the form of spectra.

Question 2: For a molecule to react with a photon, it must possess an oscillating dipole moment that matches the photon's frequency.

A. Ano

B. Ne

Explanation: A molecule can only react with a photon with frequency $\nu$ if it possesses (at least transiently) an oscillating dipole with the same frequency $\nu$.

Question 3: Which of the following statements accurately describe phenomena in absorption and emission spectroscopy?

A. Excitation of a molecule to an excited state occurs when a photon's energy is absorbed.

B. A photon's energy is simultaneously absorbed and emitted during the process.

C. Relaxation from an excited state involves the emission of a photon's energy.

D. The energy of a photon absorbed or emitted is given by the formula h u = |E_1 - E_2|.

Explanation: In absorption spectroscopy, excitation to an excited state happens when a photon's energy is absorbed. In emission spectroscopy, relaxation from an excited state occurs as a photon's energy is emitted. For both processes, the energy of the photon absorbed or emitted is equal to the absolute difference between the initial and final energy levels, expressed as h u = |E_1 - E_2|. The simultaneous absorption and emission of a photon is characteristic of Raman spectroscopy, not absorption and emission spectroscopy.

Question 4: Molecular spectroscopy involves the interaction of molecules with electromagnetic radiation to deduce which type of information?

A. Structural information, such as bond lengths and angles

B. Electronic transitions

C. Vibrational motion

D. Rotational motion

Explanation: Molecular spectroscopy is defined as the interaction of molecules with electromagnetic radiation in order to deduce structural information. The study materials also indicate that molecules are much more complex than atoms due to rotational motion, vibrational motion, and electronic transitions, all of which are probed by molecular spectroscopy to gather this structural information.

Question 5: The total number of vibrational modes for a polyatomic molecule is always equal to 3N, where N is the number of atoms.

A. Ano

B. Ne

Explanation: For a polyatomic molecule with N atoms, there are 3N total modes. However, 3 modes correspond to the total molecule's displacement and are subtracted. Additional modes can also be subtracted based on angle specifications.