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Why cold gas is used for producing an absorption line spectrum
I suppose that if that cold gas was hot and we passed white light through it, we will get the complete spectrumwukunlin said:I am assuming hot/cold is defined by the population proportion in the relevant energy levels that correspond to the absorption/emission lines. Each line correspond to the difference between 2 energy levels, a higher and a lower level.
In "hot" gases, more molecules1 are at the the higher energy level. Over time they decay to the lower level and give you the emission lines. If you try to make absorption lines in "hot" gases then your absorption lines will be very weak because there isn't a lot of molecules at the lower level for you to excite into the higher level.
To get a nice absorption spectrum you want the gas to be "cold," so you get lots of molecules at the lower level. When the white light source goes through the gas, a lot of molecules absorb light at relevant frequencies and get bumped up to higher levels.
1 I say it this way to make it easier to read but it isn't exactly true. It is the electrons in the molecules that move between the energy levels, not the molecules themselves.
I don't really agree with your self-correction.wukunlin said:1 I say it this way to make it easier to read but it isn't exactly true. It is the electrons in the molecules that move between the energy levels, not the molecules themselves.
sophiecentaur said:I don't really agree with your self-correction.
In the case of light absorption, it is 'convenient' to talk in terms of the electron's energy levels but, in truth, it is the energy levels of the whole system that count. It just happens that the relative masses of an electron and a nucleus are so different that we tend to ignore the tail wagging the dog - but the nucleus is still a part of what happens. In some cases of molecular absorption, two nuclei will be of very similar (or the same) mass. But, of course, the frequencies involved will be much lower than optical.
ElmorshedyDr said:If solid was heated instead of a gas will the result be continuous spectrum ??
ElmorshedyDr said:It's a pretty old topic, but when revising atomic spectra some new questions came up in my mind, so I liked to just do it on this topic instead of a new one, however,
Why doesn't discrete spectra (emission - absorption ) appear in gases of relatively high pressure , liquids, solids, it seams that only low pressure gases is the only suitable state, why is that?
UltrafastPED said:In short, "pressure broadening" ... the atoms are set to moving faster, but as always, in random directions. This results in Doppler shifts in the spectrum.
UltrafastPED said:In short, "pressure broadening" ... the atoms are set to moving faster, but as always, in random directions. This results in Doppler shifts in the spectrum.
UltrafastPED said:This is for a gas, nasu. And whether you call it pressure broadening, or temperature broadening - it has the same root cause.
UltrafastPED said:This is for a gas, nasu. And whether you call it pressure broadening, or temperature broadening - it has the same root cause.
nasu said:He asked about high liquids and solids, besides the high pressure gases.
You did not mention that your answer is aimed at high pressure gases only.
The energy bands that appear due to the collective behavior of atoms closely packed in condensed matter is not due to Doppler. Possible that we look at the question from different points of view.
"Pressure broadening" seems to be a series of phenomena not quite related to Doppler shifts (from what they say on wikipedia). But I suppose you may be more familiar with this field.
voko said:but the surface of the Sun radiates mostly in the visible part of the spectrum.
klimatos said:Depending upon where you place the dividing lines, solar radiation at the outside of the Earth's atmosphere is roughly 46% infrared, 9% ultraviolet, and only 45% visible.
An absorption line spectrum is a type of spectrum that is produced when light passes through a material and certain wavelengths are absorbed by the material. This results in dark lines in the spectrum, which can be used to identify the elements present in the material.
An absorption line spectrum is produced when light passes through a material, while an emission line spectrum is produced when a material emits light. In an absorption line spectrum, certain wavelengths of light are absorbed, resulting in dark lines, while in an emission line spectrum, certain wavelengths of light are emitted, resulting in bright lines.
The dark lines in an absorption line spectrum are caused by the absorption of specific wavelengths of light by the atoms or molecules in the material. Each element has a unique set of energy levels, and when light of a particular wavelength is absorbed, it causes an electron in the atom or molecule to move to a higher energy level, resulting in a dark line in the spectrum.
An absorption line spectrum is an important tool in astronomy as it allows scientists to identify the elements present in a star or other celestial object. By analyzing the dark lines in the spectrum, scientists can determine the chemical composition of the object and gain insights into its physical properties.
Yes, an absorption line spectrum can change over time. This can happen if the material through which light is passing changes, such as when a star evolves and its chemical composition changes. It can also occur if the light source itself changes, as in the case of a variable star. Scientists can use these changes in the absorption line spectrum to study the evolution of stars and other celestial objects.