Dipole moment

The electric dipole moment is a measure of polarity. It is the second term in a multipole expansion of a field (the first one being the monopole, or Coulombic, term.) Its definition, for a system of point charges, is $\mathbf {p} =\sum _{i=1}^{N}\,q_{i}\,\mathbf {r} _{i}.$

For molecular systems, it is customarily given in units of Debyes, after the physicist Peter J. W. Debye. In SI units, $1$D equals approximately $3.33564\times 10^{-30}$ Coulomb-meter (exactly $10^{-21}$C mFailed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle ^2} /s divided by Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle c} , the speed of light in vacuum). Conversely, 1 C m = Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 2.9979 10^{29}} D. This is unit is convenient for molecular systems since 1Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \AA \times 1 e=4.803} D.