What are the main types of molecular vibrations and their subtypes?

Stretching Vibrations: These involve a change in the bond length between two atoms along the bond axis.

• Symmetric stretching: Both bonds in a group stretch and contract in phase.
• Asymmetric stretching: One bond stretches while the other contracts, or they stretch and contract out of phase.

Bending Vibrations (also called deformation vibrations): These involve a change in the angle between two bonds or the movement of a group of atoms with respect to the rest of the molecule.

• In-plane bending:
  • Scissoring: Two atoms move towards and away from each other, decreasing and increasing the bond angle.
  • Rocking: The entire group of atoms moves back and forth in the same plane.
• Out-of-plane bending:
  • Wagging: The group of atoms moves out of the plane, either both atoms moving up or both moving down.
  • Twisting: One atom moves up out of the plane while the other moves down, or vice versa.