The x-axis for IR spectroscopy records wavenumber, typically measured in units of inverse centimeters (cm^-1). Wavenumber is directly proportional to energy. It corresponds to the number of waves per unit length and is related to the frequency (and therefore energy) of the absorbed or transmitted light. According to the Planck relation, energy (E) is directly proportional to frequency (ν):
E = hν
where h is Planck's constant and ν is the frequency of the light.
Replacing frequency with wavenumber (σ) and the speed of light (c), we find:
ν = cσ
Therefore, the energy of the photon absorbed or scattered in IR spectroscopy can be expressed as:
E = hcσ
Since h (Planck's constant) and c (speed of light) are constants, the energy is directly proportional to the wavenumber (σ), and thus the x-axis scale based on wavenumber is a direct measure of the relative energies of molecular vibrations or rotations being probed in IR spectroscopy.
The X-axis for IR spectroscopy records ___ which is directly proportional to energy
3 answers
is another word for frequency wavenumber?
No, frequency and wavenumber are related but distinct concepts.
- **Frequency** (ν): Frequency is the number of cycles (or wave peaks) that pass a given point per unit time. It is measured in units of Hertz (Hz), which are equivalent to cycles per second.
- **Wavenumber** (σ or sometimes k): Wavenumber is a spatial frequency, representing the number of wave cycles in a unit of distance. It is usually measured in inverse meters (m^-1) or, in the context of infrared (IR) spectroscopy, more commonly in inverse centimeters (cm^-1).
The relation between frequency (ν), wavenumber (σ), and the speed of light (c) in vacuum is given by the equation:
ν = cσ
where:
- ν is the frequency
- c is the speed of light (approximately 3.0 x 10^8 meters per second)
- σ is the wavenumber
From this relation, you can see that the frequency and wavenumber are directly proportional to each other: as the frequency of a wave increases, so does its wavenumber, and vice versa. However, they are not interchangeable terms. Frequency refers to how often the wave oscillates over time, while wavenumber refers to how many waves are present over a certain spatial extent. In spectroscopy, we often use wavenumber because it is directly proportional to the energy of the photons being absorbed or emitted.
- **Frequency** (ν): Frequency is the number of cycles (or wave peaks) that pass a given point per unit time. It is measured in units of Hertz (Hz), which are equivalent to cycles per second.
- **Wavenumber** (σ or sometimes k): Wavenumber is a spatial frequency, representing the number of wave cycles in a unit of distance. It is usually measured in inverse meters (m^-1) or, in the context of infrared (IR) spectroscopy, more commonly in inverse centimeters (cm^-1).
The relation between frequency (ν), wavenumber (σ), and the speed of light (c) in vacuum is given by the equation:
ν = cσ
where:
- ν is the frequency
- c is the speed of light (approximately 3.0 x 10^8 meters per second)
- σ is the wavenumber
From this relation, you can see that the frequency and wavenumber are directly proportional to each other: as the frequency of a wave increases, so does its wavenumber, and vice versa. However, they are not interchangeable terms. Frequency refers to how often the wave oscillates over time, while wavenumber refers to how many waves are present over a certain spatial extent. In spectroscopy, we often use wavenumber because it is directly proportional to the energy of the photons being absorbed or emitted.