The debye (symbol: D) is a CGS unit[1] (a non-SI metric unit) of electric dipole moment[note 1] named in honor of the physicist Peter J. W. Debye. It is defined as 1×10−18 statcoulomb-centimeter.[note 2] Historically the debye was defined as the dipole moment resulting from two charges of opposite sign but an equal magnitude of 10-10 statcoulomb[note 3] (generally called e.s.u. (electrostatic unit) in older literature), which were separated by 1 ångström.[note 4] This gave a convenient unit for molecular dipole moments.
1 D | = 10-18 statC·cm |
= 10-10 esu·Å[note 2] | |
= 1⁄299,792,458×10−21 C·m[note 5] | |
≈ 3.33564×10−30 C·m | |
≈ 1.10048498×1023 qPlP | |
≈ 0.393430307 ea0[2] | |
≈ 0.20822678 eÅ |
Typical dipole moments for simple diatomic molecules are in the range of 0 to 11 D. Symmetric homoatomic species, e.g. chlorine, Cl2, have zero dipole moment and highly ionic molecular species have a very large dipole moment, e.g. gas phase potassium bromide, KBr, with a dipole moment of 10.5 D.[3]
The debye is still used in atomic physics and chemistry because SI units are inconveniently large. The smallest SI unit of electric dipole moment is the yoctocoulomb-meter, which is roughly 300,000 D.[note 6] There is currently no satisfactory solution to this problem of notation without resorting to the use of scientific notation.
1 statC | =1 Fr |
=1 esu |
1 Å | = 100 pm |
= 10-8 cm | |
= 10-10 m |