Exploring the Interaction of EM Waves & Molecular Vibrations

[Harmony]

Quote from Organic Chemistry, L.G. Wade, Jr.:
"Not all molecular vibrations absorb IR radiation."
"One of the component of an electromagnetic wave is E field. This field alternately stretches and compresses a polar bond."
"If this alternate stretching compressing of the bond occurs at the frequency of the molecule's natural rate of vibration, energy may be absorbed."
"If a bond has zero dipole moment, the E field doesn't interact with the bond."

Things that I am confuse with:
1. If there's no interaction with EM wave, does a molecule still vibrate? If so, what will be the frequency of the molecule? Is it temperature dependent? Or is it the lowest frequency possible?

2. Is the vibrational energy quantized? Eg. A molecule has 3 different mode of vibration. The frequency of each different mode of vibration is 10Hz, 20Hz and 30Hz. Does this means that the molecule can ONLY vibrate in ONE of these three frequency? i.e. Frequency of 10.1 Hz, 15 Hz, 22 Hz etc. is disallowed?

3. What happens if the EM wave radiated on the molecule is not the same as the neutral vibrational frequency? It wouldn't be absorbed, but will the E field interacts with the molecule? eg. Increasing the frequency of the vibration frequency?

4. Would the result of IR spectroscopy influenced by surrounding temperature?

5. Why is EM wave absorbed when it is the same as the natural frequency? Is the Em wave energy absorbed in order to change the ground state vibrational energy to another natural frequency?

Thanks for your time.

 

[Valerie Park]

1. If there's no interaction with EM wave, does a molecule still vibrate? If so, what will be the frequency of the molecule? Is it temperature dependent? Or is it the lowest frequency possible?Yes, molecules still vibrate even if there is no interaction with an EM wave. The frequency of the molecule is generally temperature dependent and varies depending on the type of molecule and its size. The lowest frequency possible is typically known as the fundamental vibration frequency of the molecule. 2. Is the vibrational energy quantized? Eg. A molecule has 3 different mode of vibration. The frequency of each different mode of vibration is 10Hz, 20Hz and 30Hz. Does this means that the molecule can ONLY vibrate in ONE of these three frequency? i.e. Frequency of 10.1 Hz, 15 Hz, 22 Hz etc. is disallowed?No, the vibrational energy of a molecule is not quantized; it can vibrate at any frequency within a certain range, including frequencies between the three frequencies mentioned (10.1 Hz, 15 Hz, 22 Hz etc.). 3. What happens if the EM wave radiated on the molecule is not the same as the neutral vibrational frequency? It wouldn't be absorbed, but will the E field interacts with the molecule? eg. Increasing the frequency of the vibration frequency?If the EM wave is not the same as the neutral vibrational frequency, then it will not be absorbed by the molecule. However, the E field can interact with the molecule, potentially increasing the vibrational frequency of the molecule. 4. Would the result of IR spectroscopy influenced by surrounding temperature?Yes, the result of IR spectroscopy can be influenced by the surrounding temperature. As the temperature increases, the vibrational frequencies of a molecule may change, resulting in a different IR spectrum. 5. Why is EM wave absorbed when it is the same as the natural frequency? Is the Em wave energy absorbed in order to change the ground state vibrational energy to another natural frequency?When an EM wave is the same as the natural frequency of a molecule, the energy from the EM wave is absorbed by the molecule, raising the vibrational energy of the molecule to a higher energy level. This energy can then be used to excite the molecule to a higher vibr

 

[sir-pinski]

1. Yes, a molecule can still vibrate even if there is no interaction with an EM wave. The frequency of the molecule's vibration is dependent on its natural rate of vibration, which is determined by its bond strengths and masses of the atoms involved. This frequency is not temperature dependent, but the amplitude of the vibration may change with temperature.

2. Yes, vibrational energy is quantized, meaning that the molecule can only vibrate at certain frequencies. In your example, the molecule can only vibrate at 10Hz, 20Hz, or 30Hz. Frequencies in between these values are not allowed.

3. If the EM wave is not at the same frequency as the molecule's natural rate of vibration, the E field may still interact with the molecule and cause it to vibrate at a different frequency. This is known as Raman scattering and can provide information about the molecule's structure.

4. Yes, the results of IR spectroscopy can be influenced by surrounding temperature. As temperature increases, molecules may vibrate with greater amplitude, which can result in broadening of the IR absorption peaks.

5. When an EM wave is absorbed at the same frequency as the molecule's natural rate of vibration, it provides the energy needed for the molecule to change its vibrational state. This is known as a vibrational transition and can result in the absorption of the EM wave.