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The SI unit of molar absorption coefficient is the square metre per mole (m 2 /mol), but in practice, quantities are usually expressed in terms of M −1 ⋅cm −1 or L⋅mol −1 ⋅cm −1 (the latter two units are both equal to 0.1 m 2 /mol). In older literature, the cm 2 /mol is sometimes used; 1 M −1 ⋅cm −1 equals 1000 cm 2 /mol.
A barn (symbol: b) is a metric unit of area equal to 10 −28 m 2 (100 fm 2).This is equivalent to a square that is 10 −14 m (10 fm) each side, or a circle of diameter approximately 1.128 × 10 −14 m (11.28 fm).
Wavenumber has dimensions of reciprocal length, so its SI unit is the reciprocal of meters (m −1). In spectroscopy it is usual to give wavenumbers in cgs unit (i.e., reciprocal centimeters; cm −1 ); in this context, the wavenumber was formerly called the kayser , after Heinrich Kayser (some older scientific papers used this unit ...
The centimetre (SI symbol: cm) is a unit of length in the metric system equal to 10 −2 metres ( 1 / 100 m = 0.01 m). To help compare different orders of magnitude , this section lists lengths between 10 −2 m and 10 −1 m (1 cm and 1 dm).
For example, the reciprocal centimetre, cm −1, is an energy unit equal to the energy of a photon with a wavelength of 1 cm. That energy amounts to approximately 1.24 × 10 −4 eV or 1.986 × 10 −23 J. The energy is inversely proportional to the size of the unit of which the reciprocal is used, and is proportional to the number of ...
A medium with a permeability of 1 darcy permits a flow of 1 cm 3 /s of a fluid with viscosity 1 cP (1 mPa·s) under a pressure gradient of 1 atm/cm acting across an area of 1 cm 2. Typical values of permeability range as high as 100,000 darcys for gravel, to less than 0.01 microdarcy for granite. Sand has a permeability of approximately 1 darcy ...
The SI has special names for 22 of these coherent derived units (for example, hertz, the SI unit of measurement of frequency), but the rest merely reflect their derivation: for example, the square metre (m 2), the SI derived unit of area; and the kilogram per cubic metre (kg/m 3 or kg⋅m −3), the SI derived unit of density.
This traditional unit is often called a molar and denoted by the letter M, for example: 1 mol/m 3 = 10 −3 mol/dm 3 = 10 −3 mol/L = 10 −3 M = 1 mM = 1 mmol/L. The SI prefix "mega" (symbol M) has the same symbol. However, the prefix is never used alone, so "M" unambiguously denotes molar.