Emission spectra of a hot body vs. atomic emission spectra

In summary, the conversation discusses the presence of the characteristic yellow emission band of Na in a thermal spectrum of pure Fe at high temperatures. While the Na band is not expected to be present in the Fe emission spectra, the conversation suggests that it may still be visible due to thermal broadening and the close spacing of emitted frequencies in a black body's thermal spectrum. This phenomenon is also observed in molecular spectra and is due to the thermal motion of atoms and their closely spaced energy levels.
  • #1
afcsimoes
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Consider a piece of pure Fe hot enough to have a bright white color (about 2 000 ºC, e.g.) and the characteristic yellow narrow yellow emission of the Na atom.
Does the Na yellow band will be present at the thermal spectra of the pure Fe?
My guess: Yes.
 
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  • #2
afcsimoes said:
Does the Na yellow band will be present at the thermal spectra of the pure Fe?
characteristic Na doublet should not be present in Fe emission spectra -regarding yellow color band -in a white light emission from hot metals one expects almost all the colors in the visible region but the ultravoilet end will be stronger
 
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  • #3
In addition to above:
How atoms produce spectra - includes a section on thermal (ie. blackbody) spectra.
http://www.astronomynotes.com/light/s8.htm
"A thermal spectrum is produced by atoms that are closely packed together. The energy levels of the atoms are distorted by their neighboring atom's electrons. This smears out the normally sharp spectral lines (they become fatter)."
Related: band structure of solids.
 
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  • #4
afcsimoes said:
My guess: Yes.
some general info;

From everyday experience we know that heated solid objects emit light, and as a their temperature increases, their dominant color moves increasingly towards the blue end of the spectrum.

A blacksmith handling hot iron makes it glow a dull red, then if the coals are fanned and the temperature increases, orange.

The filament of a light bulb fed by a fading battery also glows orange, while a fresh battery makes the light bulb glow yellow-white.
 
  • #5
A black body radiates energy at all frequencies.
That's why i say Yes, the Yellow Na characteristic radiation also will be there.
 
  • #6
The "why it is like that" question is the next level to answer.
Someone knows?
 
  • #7
afcsimoes said:
A black body radiates energy at all frequencies.
That's why i say Yes, the Yellow Na characteristic radiation also will be there.
characteristic emission lines are signature of energy levels participating in the the transition of electron -the lines will be sharper if the levels are sharp.
in thermal emission as the states are so much energetically excited and have all possible oscillations the the lines will get broadened - thermal broadening is an area being explored by spectroscopists.
i feel that that at high temperatures the photons of all possible energies get emitted and the intensity of various frequency range get to the wien's curve of black body radiation and its a continuous curve ,so the emitted frequencies are closely spaced.
these bands are also observed in 'molecular spectra' where the degrees of freedom of molecules lead to to rotation -vibration frequencies.something of this nature is happening in thermal motion of various types leading to closely spaced energy levels.
 
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1. What is the difference between emission spectra of a hot body and atomic emission spectra?

The emission spectra of a hot body refers to the continuous spectrum of light emitted by a hot object, such as a star or a light bulb. This spectrum contains all wavelengths of light, from infrared to ultraviolet. On the other hand, atomic emission spectra refer to the discrete lines of color emitted by excited atoms of a particular element when they release energy. These lines are characteristic of each element and can be used for identification.

2. How are emission spectra of a hot body and atomic emission spectra measured?

Emission spectra of a hot body can be measured using a spectrometer, which separates the different wavelengths of light emitted by the hot object. This creates a continuous spectrum that can be analyzed. Atomic emission spectra, on the other hand, can be measured using a spectroscope, which uses a diffraction grating to separate the different wavelengths of light emitted by excited atoms.

3. What causes the emission spectra of a hot body and atomic emission spectra?

The emission spectra of a hot body is caused by the thermal energy of the object. As the object heats up, the atoms and molecules within it vibrate and release energy in the form of light. Atomic emission spectra, on the other hand, are caused by the excitation of atoms. When atoms are excited, their electrons jump to higher energy levels and then release this energy in the form of light as they return to their ground state.

4. Can emission spectra of a hot body and atomic emission spectra be used for different purposes?

Yes, emission spectra of a hot body and atomic emission spectra can be used for different purposes. Emission spectra of a hot body can be used to determine the temperature and composition of a hot object, such as a star. Atomic emission spectra, on the other hand, can be used for identification and analysis of elements in various samples, such as in forensic science or environmental testing.

5. How are emission spectra of a hot body and atomic emission spectra related to each other?

Emission spectra of a hot body and atomic emission spectra are related in that they both involve the emission of light by excited particles. However, the two types of spectra have different origins and characteristics. Emission spectra of a hot body are continuous and contain all wavelengths of light, while atomic emission spectra are discrete and contain only specific wavelengths of light. Additionally, while emission spectra of a hot body are influenced by the temperature and composition of the object, atomic emission spectra are specific to the element being analyzed.

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