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Wavenumber, as used in spectroscopy and most chemistry fields, is defined as the number of wavelengths per unit distance, typically centimeters (cm −1): ~ =, where λ is the wavelength. It is sometimes called the "spectroscopic wavenumber". [1] It equals the spatial frequency.
Spatial frequency is a reciprocal length, which can thus be used as a measure of energy, usually of a particle. 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.
where Δν̃ is the Raman shift expressed in wavenumber, λ 0 is the excitation wavelength, and λ 1 is the Raman spectrum wavelength. Most commonly, the unit chosen for expressing wavenumber in Raman spectra is inverse centimeters (cm −1). Since wavelength is often expressed in units of nanometers (nm), the formula above can scale for this ...
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.
Frequencies observed in astronomy range from 2.4 × 10 23 Hz (1 GeV gamma rays) down to the local plasma frequency of the ionized interstellar medium (~1 kHz). Wavelength is inversely proportional to the wave frequency, [1] so gamma rays have very short wavelengths that are fractions of the size of atoms, whereas wavelengths on the opposite end ...
One flick corresponds to a spectral radiance of 1 watt per steradian per square centimeter of surface per micrometer of span in wavelength (W·sr −1 ·cm −2 ·μm −1). This is equivalent to 10 10 watts per steradian per cubic meter (W·sr −1 ·m −3). In practice, spectral radiance is typically measured in microflicks (10 −6 flicks). [1]
Here the coefficient A is an approximation of the short-wavelength (e.g., ultraviolet) absorption contributions to the refractive index at longer wavelengths. Other variants of the Sellmeier equation exist that can account for a material's refractive index change due to temperature , pressure , and other parameters.
For example, with one point per wavelength of a HeNe reference laser at 0.633 μm (15 800 cm −1) the shortest wavelength would be 1.266 μm (7900 cm −1). Because of aliasing , any energy at shorter wavelengths would be interpreted as coming from longer wavelengths and so has to be minimized optically or electronically.
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