The dynamical motion of chemically bound atoms which constantly change
their position with each other. The vibration of molecules is treated within
→ quantum theory. Therefore, the energy of molecular vibration
can only take → discrete values.
To a first approximation, molecular vibrations can be approximated as
→ simple harmonic oscillator assigned to each mode.

In a → linearly polarized light,
a plane perpendicular to the → plane of polarization
and containing
the direction of propagation of light. It is also the plane containing the direction of
propagation and the electric vector (E) of the electromagnetic light wave.

1) The act of vibrating. The state of being vibrated.
2) A continuing → periodic
→ oscillation relative to a fixed reference point or
→ equilibrium state.

The energy due to the vibration of the molecules making up atoms
(→ molecular vibration). A molecule in space can
have energies in various forms: → rotational energy,
vibrational energy, or electronic energy. These energies of
molecules are → quantized and a particular molecule
can exist in different rotational and vibrational
→ energy levels. The molecules
can move from one level to another level only by a jump
involving a finite amount of energy. → Quantum mechanics
predicts that any molecule can never have zero vibrational energy,
that is atoms can never be completely at rest relative to each other.
The harmonically oscillating molecules can undergo vibrational changes
determined by simple selection rules obtained from
→ Schrödinger equation.

The frequency at which the atoms in a molecule vibrate. The frequencies of
→ molecular vibrations in diatomic molecules
are in the order of 10^{-12} to 10^{-14} Hz. In such molecules,
the only → vibrational mode available is along the bond.
More complicated molecules have many types of vibration and stretching modes.

Any of the ways in which a → molecule vibrates. Each
vibrational mode has a different → frequency
frequency. The number of vibrational modes of a molecule
is determined by the number of atoms in it. The number of vibrational modes for a
non-linear molecule is 3N - 6, where N is the number of atoms
making up the molecule. For a linear molecule it is 3N - 5.