Absorbtion lines in spectrum question

In summary, when a shining white light is passed through a gas of vaporized elements, it causes absorption lines to be created in the spectrum. These lines are unique to each element and are caused by the absorption and re-emission of photons by excited electrons. The direction of the re-emitted light depends on the spherical symmetry of the atom, unless there is something present to break that symmetry. This process is different from Compton scattering, which involves ionization, and Raman or Rayleigh scattering, which does not involve ionization.
  • #1
AStaunton
105
1
shining white light through a gas of a vapourised element causes absorbtion lines to be created in the white light spectrum ie. there are dark lines running through the otherwise continuous spectrum and the position of these lines are unique to particular element.


Why is it though that we see these lines at all considering that when an electron absorbs a photon it and goes into an excited state it is only there for a very short period of time before it re-emits a photon of that wavelength again, ie an atom absorbs the photon but then re-emits it very quickly after. I can't see then, why the effect is that we see dark lines.
 
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  • #2
The re-emitted light is in all directions, so only a small part of it actually ends up entering your eyes.
 
  • #3
jtbell said:
The re-emitted light is in all directions, so only a small part of it actually ends up entering your eyes.

While I know (I think) that Compton scattering and this are different, how is it that they are different?
 
  • #4
what determines the direction of the reemitted light?
 
  • #5
The Brewster's angle i think!
 
  • #6
khemist said:
While I know (I think) that Compton scattering and this are different, how is it that they are different?

Compton scattering involves ionization. Scattering of light without ionization is Raman or Rayleigh scattering.
Absorption and re-emission (fluorescence) is different from scattering because it occurs at an altogether different timescale. In short, you can measure the atom to be in the excited state during fluorescence, but not during scattering.
 
  • #7
AStaunton said:
what determines the direction of the reemitted light?

For an individual atom, which we're talking about here, you have spherical symmetry. The photon is equally likely to be emitted in all directions.
If there's something around there to break that symmetry, then the situation becomes different, and it'd depend on which states the transition was between.
 

What are absorption lines in spectrum?

Absorption lines in spectrum refer to dark lines that appear in the spectrum of light emitted from a source, indicating the wavelengths of light that have been absorbed by a material. These lines are caused by the absorption of specific frequencies of light by atoms or molecules in the material.

How are absorption lines in spectrum used in science?

Absorption lines in spectrum are used in various scientific fields, such as astronomy, chemistry, and physics. They can provide information about the composition, temperature, and other properties of a material. In astronomy, absorption lines are used to study the composition of stars and galaxies. In chemistry, they can be used to identify the elements present in a sample. In physics, absorption lines can be used to study the behavior of atoms and molecules.

What causes absorption lines in spectrum?

The absorption lines in spectrum are caused by the absorption of specific frequencies of light by atoms or molecules. When light passes through a material, certain frequencies are absorbed by the atoms or molecules, causing dark lines to appear in the spectrum. The remaining frequencies of light are then transmitted, producing the characteristic pattern of dark and light lines in the spectrum.

How are absorption lines different from emission lines?

Absorption lines are dark lines in the spectrum, whereas emission lines are bright lines. Absorption lines are caused by the absorption of specific frequencies of light by atoms or molecules, while emission lines are caused by the emission of specific frequencies of light by excited atoms or molecules. Absorption lines appear in the spectrum of light passing through a material, while emission lines appear in the spectrum of light emitted by a material.

Can absorption lines be used to determine the composition of a material?

Yes, absorption lines can be used to determine the composition of a material. Each element or molecule has a unique pattern of absorption lines, allowing scientists to identify the elements or molecules present in a material. By analyzing the intensities and positions of the absorption lines, scientists can also determine the relative abundance of different elements or molecules in a sample.

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