What Happens to Photons During Ionization?

In summary, when a photon is used to ionize an atom, it is absorbed or annihilated, releasing the electron and any leftover energy becomes kinetic energy. The more energetic the photon, the faster the electron will be. In the photoelectric effect, the photon is 100% absorbed, while in ionization, there may be atomic emission x-rays. If the photon interacts via Thomson scattering, a secondary electron is produced. If the photon's energy falls between two quantum states, it cannot be absorbed and may lead to Compton scattering in which the electron may end up in a higher bound state. The cross section for this interaction is lower due to the involvement of two photons.
  • #1
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If a photon is used to ionize an atom then what happens to the photon? If the wavelength of the photon corresponds to the ionization energy, then the photon is absorbed/annihilated, yes? What if the photon has more energy. Is a lower energy photon emitted during ionization?
 
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  • #2
Yep, the photon would be absorbed (annihilated). The energy that was in the photon would go into releasing the electron, and if there were any energy left over, it becomes kinetic energy of the electron. So the more energetic the photon, the more energetic (faster-moving) the electron that comes out.
 
  • #3
If the photoemission is via the photoelectric effect, there is no secondary electron. The photon energy is 100% absorbed. If there is ionization, there are usually atomic emission x-rays etc. If the photon interaction is via Thomson scattering, there is a secondary electron due to photon scattering..
Bob S
 
  • #4
Thank you for the answers. However, there was one other point I was getting to. If the photon has an energy such that, if absorbed by the atom, it falls "between" two quantum states, then this photon cannot be absorbed, correct? Since the extra energy can't disappear, the absorption cross section is zero?
 
  • #5
Photons can scatter inelasitically off of bound electrons in the atom. This is Compton scattering, usually leading to an ejected electron, but occasionally the electron could end up in a higher bound quantum state. One example might be a photon with an energy exceeding 0.75 x 13.6 eV inelastically scattering off of the bound electron in a hydrogen atom, leaving the electron in a higher p state. Because two photons are involved (one incident, one leaving), the cross section (probability) is lower.
Bob S
 

FAQ: What Happens to Photons During Ionization?

What is the relationship between wavelength and ionization?

Wavelength and ionization are inversely related. This means that as the wavelength of light decreases, the energy of the light increases, making it more likely to cause ionization.

What is the threshold wavelength for ionization?

The threshold wavelength for ionization is the minimum wavelength of light required to cause ionization in a specific material. This threshold varies depending on the material and its properties.

How does the ionization potential of an atom affect its response to different wavelengths?

The ionization potential of an atom is the minimum amount of energy required to remove an electron from the atom. Atoms with a lower ionization potential will be more easily ionized by shorter wavelengths of light, while atoms with a higher ionization potential will require longer wavelengths.

Can multiple wavelengths cause ionization in the same material?

Yes, multiple wavelengths can cause ionization in the same material. However, the amount of ionization will depend on the energy of each wavelength and the properties of the material.

What are some common sources of ionizing wavelengths?

X-rays, gamma rays, and ultraviolet radiation are all common sources of ionizing wavelengths. However, any light source with enough energy can potentially cause ionization in a material.

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