Final answer:
In IR spectroscopy, the three kinds of bond vibrations that it can cause are stretching, bending, and twisting. Absorption occurs when the IR radiation frequency matches a molecule's natural vibrational frequency, leading to increased amplitude of that vibration.
Step-by-step explanation:
When discussing Infrared (IR) spectroscopy, we are often concerned with how molecules absorb IR radiation and undergo various vibrational transitions. There are three main kinds of bond vibrations that can be caused by IR spectroscopy:
- Stretching
- Bending
- Twisting
These vibrations alter the dipole moment of molecules, and for a vibration to be IR active, it must bring about a periodic change in the dipole moment. For example, the stretching of a carbonyl bond is highly polar, and thus, its vibration strongly absorbs IR radiation. This is in contrast to symmetrical double and triple bonds, which may not change the dipole moment significantly during stretching, rendering them IR inactive. The energy of molecular vibration is quantized, and when the frequency of IR radiation matches the natural vibrational frequency of a bond, the molecule absorbs this energy, resulting in an increase in the vibration amplitude without altering the frequency.