Electric Dipole Moment - Dipole Moments of Molecules

Dipole Moments of Molecules

Dipole moments in molecules are responsible for the behavior of a substance in the presence of external electric fields. The dipoles tend to be aligned to the external field which can be constant or time-dependent. This effect forms the basis of a modern experimental technique called Dielectric spectroscopy.

Dipole moments can be found in common molecules such as water and also in biomolecules such as proteins.

By means of the total dipole moment of some material one can compute the dielectric constant which is related to the more intuitive concept of conductivity. If is the total dipole moment of the sample, then the dielectric constant is given by,

$\epsilon = 1 + k \langle \mathcal{M}_{\rm Tot}^2 \rangle$

where k is a constant and is the time correlation function of the total dipole moment. In general the total dipole moment have contributions coming from translations and rotations of the molecules in the sample,

$\mathcal{M}_{\rm Tot} = \mathcal{M}_{\rm Trans} + \mathcal{M}_{\rm Rot}.$

Therefore, the dielectric constant (and the conductivity) has contributions from both terms. This approach can be generalized to compute the frequency dependent dielectric function.

Read more about this topic: Electric Dipole Moment

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