Debye

The debye ( ,{{cite web : p = qr. named in honour of the physicist Peter J. W. Debye. It is defined as statcoulomb-centimetres.The statcoulomb is also known as the franklin or electrostatic unit of charge. : 1 statC = 1 Fr = 1 esu = 1 cm3/2⋅g1/2⋅s−1. Historically the debye was defined as the dipole moment resulting from two charges of opposite sign but an equal magnitude of 10−10 statcoulomb10−10 statcoulomb corresponds to approximately 0.2083 units of elementary charge. (generally called e.s.u. (electrostatic unit) in older scientific literature), which were separated by 1 ångström.The ångström is within an order of magnitude of the nuclear separation for a typical covalent bond. : 1 Å = 100 pm = 10−8 cm = 10−10 m. This gave a convenient unit for molecular dipole moments.

Typical dipole moments for simple diatomic molecules are in the range of 0 to 11 D. Molecules with symmetry point groups or containing inversion symmetry do not have a permanent dipole moment, while highly ionic molecular species have a very large dipole moment, e.g. gas-phase potassium bromide, KBr, with a dipole moment of 10.41 D. A proton and an electron 1 Å apart have a dipole moment of 4.8 D.

The debye is still used in atomic physics and chemistry because SI units have until recently been inconveniently large. The smallest SI unit of electric dipole moment is the quectocoulomb-metre,With a value of 10−30, quecto- is the smallest SI prefix, accepted as an SI prefix by the CGPM on 18 November 2022. which corresponds closely to 0.3 D.