Debye
The debye (symbol: D) (ångström.[note 4] This gave a convenient unit for molecular dipole moments.
1 D = 10−18 statC·cm = 10−18 cm5/2⋅g1/2⋅s−1 [note 5] = 10−10 statC·Å [note 2] ≘ 1/299792458×10−21 C·m[note 6] ≈ 3.33564×10−30 C·m [note 7] ≈ 0.3934303 e·a0 [note 8] ≈ 0.2081943 e⋅Å ≈ 0.02081943 e·nm
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 10.41 D.[3] 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,[note 9] which corresponds closely to 0.3 D.
See also
- Buckingham (unit) (CGS unit of electric quadrupole)
Notes
- ^ Two equal and opposite charges separated by some distance constitute an electric dipole. This dipole possesses an electric dipole moment whose value is given as charge times length of separation. The dipole itself is a vector whose direction coincides with the position vector of the positive charge with respect to the negative charge:
- p = qr.
- ^ a b 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.
- ^ 10−10 statcoulomb corresponds to approximately 0.2083 units of elementary charge.
- ^ 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.
- CGS systems, electromagnetic units are expressed in terms of the three base units, cm, g and s, albeit the systems are mutually inconsistent in this regard.
- ^ One debye corresponds to 10−21 C·m2/s divided by the speed of light. Conversely, 1 C·m ≘ 2.9979×1029 D.
- ^ Also expressible as 3.33564 qC·m.
- atomic unit of electric dipole moment (see Atomic unit of electric dipole moment, NIST.)
- SI prefix, accepted as an SI prefix by the CGPM on 18 November 2022.