The relationship b/w infrared, temperature, and electron excitation

  • #1
Homework Statement:: 1. Does the increase in kinetic energy in (for example) water that results from increasing its temperature result from electron excitation (i.e. increasing electron energy levels) or simply increasing their velocity or vibration amplitude/frequency?

2. If excitation is involved, does that mean by definition that gases > liquids > solids in terms of the magnitude of excitation?

3. If the previous 2 are true in relation to excitation, and since electromagnetic radiation is emitted when an excited electron transitions back toward its ground state, is the transmission of heat (i.e. infrared) rays due to the loss of electron excitation?

bonus. If I shine an extremely bright light on a leaf, it will excite electrons on the magnesium in p680 and p700. If I suddenly cut off the light source, for a split second will the p680 and p700 release the same wavelength of light, or could it be changed from input to output?
Relevant Equations:: E = -R/n^2 (and other variations of the Rydberg equation)
E = energy of electron
R = Rydberg unit of energy = 2.18 x 10^-18 J/electron
n = principle quantum number

I was reviewing basic quantum mechanics and couldn't answer these question with 100% confidence when my mind asked them. My current dominant theory is that increasing temperature increases electron excitation, which means that different phases have different excitation ranges. This fits with the fact that lowering an electron's excitation (e.g. by lowering temperature) releases electromagnetic radiation (e.g. infrared). I think this is correct, but I want to make sure I'm not erring in my thought process.

For the bonus I know that the magnesium will try to go back toward its ground state to be more stable. I highly doubt that the released electromagnetic radiation would necessarily be the same wavelength that excited it in the first place, but it would be very interesting if it necessarily was.
 

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  • #2
Ok for the bonus I see now that an atomic emission spectrum could be used if the initial and end excitation states are known. Similar examples are the Lyman series and Paschen series for hydrogen.
 
  • #3
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Compare typical thermal energy of a simple molecule at the room temperature (order of kT) with typical electron excitation energy of a molecule that absorbs/emits in the visible part of the spectrum. Does it sound feasible for a molecule to have enough energy to get excited?
 
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  • #4
at 298 K, kT is 4.11E-21 J this is a molecule's thermal energy at room temperature
at 6000 K, kT is 8.28E-19 J this is the energy that molecules in the sun's photosphere are at to emit visible light (about 20x more energy than room temperature, which is unreasonably high to account for every little temperature change)

I'm pretty sure think this means that excited energy levels are not associated with "normal" phase or temperature changes. Random small temperature increases must just increase either the vibration frequency or amplitude of electrons. Since only specific quanta can excite an electron to the next level, the same quanta will be released upon demotion of the electrons (so when p700 loses its excitation, it must release some 700nm light, as that corresponds to the quanta that it absorbed).

This leads me to a couple more questions.
1. Do infrared cameras detect humans and animals because of reflected IR, or are some of our atoms excited enough to emit IR?
2. Are amplitude and frequency of electron movements related, or completely separate (I think I remember from an early chemistry class that temperature only has to do with the average kinetic energy associated with vibration, not amplitude)?
 
  • #5
chemisttree
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This leads me to a couple more questions.
1. Do infrared cameras detect humans and animals because of reflected IR, or are some of our atoms excited enough to emit IR?
2. Are amplitude and frequency of electron movements related, or completely separate (I think I remember from an early chemistry class that temperature only has to do with the average kinetic energy associated with vibration, not amplitude)?
Infrared cameras detect infrared radiation. The camera cannot distinguish between emission and reflection. It detects both. I suppose you could distinguish reflected IR if it was polarized in some way and you equipped a camera with some kind of polarizing filter.

I have no idea what you mean by “frequency and amplitude of electron movements.”
 
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  • #6
Infrared cameras detect infrared radiation. The camera cannot distinguish between emission and reflection. It detects both. I suppose you could distinguish reflected IR if it was polarized in some way and you equipped a camera with some kind of polarizing filter.

I have no idea what you mean by “frequency and amplitude of electron movements.”
That makes sense, because there isn't any logical reason that an IR camera would be able to only detect emission but not reflection. I think that the reason animals show up so well in IR is because they use lots of cellular respiration, which must produce some IR, as it is exothermic.
I guess only the amplitude of vibration is important for my purposes: it has to do with crystal lattices, as well as phase changes, but not so much individual atoms. At higher temperatures, atoms in a lattice vibrate with higher amplitudes (I assume this has something to do with electrons having a higher amplitude of vibration too). If the amplitude of vibration is made long enough, a solid will melt or a liquid will evaporate. If I understand it correctly, a single atom technically doesn't have a phase, it simply exists (but maybe it could be considered a gas, depending if it is floating or stagnant).
 
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That makes sense, because there isn't any logical reason that an IR camera would be able to only detect emission but not reflection. I think that the reason animals show up so well in IR is because they use lots of cellular respiration, which must produce some IR, as it is exothermic.
I guess only the amplitude of vibration is important for my purposes: it has to do with crystal lattices, as well as phase changes, but not so much individual atoms. At higher temperatures, atoms in a lattice vibrate with higher amplitudes (I assume this has something to do with electrons having a higher amplitude of vibration too). If the amplitude of vibration is made long enough, a solid will melt or a liquid will evaporate. If I understand it correctly, a single atom technically doesn't have a phase, it simply exists (but maybe it could be considered a gas, depending if it is floating or stagnant).
You need to learn about vibrational spectrum. It has nothing to do with atomic transition or "... frequency and amplitude of electron movements..."

https://www.chem.ucla.edu/~harding/ec_tutorials/tutorial31.pdf

The IR radiation is typically due to such vibrations.

Zz.
 
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  • #8
You need to learn about vibrational spectrum. It has nothing to do with atomic transition or "... frequency and amplitude of electron movements..."

https://www.chem.ucla.edu/~harding/ec_tutorials/tutorial31.pdf

The IR radiation is typically due to such vibrations.

Zz.
So this means an electron's excitation is associated with the vibrational state of the bond/orbital. I think this sounds similar to increasing the amplitude, but maybe I pulled that phrase out of nothing. A specific wavelength of photon absorbed corresponds to a specific quanta of energy that a bond is excited by, and a specific bond can only absorb a specific set of wavelengths of photons. When a molecule reverts back to its ground state, it emits EM radiation according to the change in excitation.
I read some more about temperature and I think that it just has to do with the speed of electrons. If temperature is raised enough, as mentioned before, excitation can also be achieved. Additionally, all objects emit some IR.
Basically, excitation has to do with electron vibrational states (and energy levels), while temperature has to do with the actual speed of electrons through space. Is this more correct?
 
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So this means an electron's excitation is associated with the vibrational state of the bond/orbital. I think this sounds similar to increasing the amplitude, but maybe I pulled that phrase out of nothing. A specific wavelength of photon absorbed corresponds to a specific quanta of energy that a bond is excited by, and a specific bond can only absorb a specific set of wavelengths of photons. When a molecule reverts back to its ground state, it emits EM radiation according to the change in excitation.
I read some more about temperature and I think that it just has to do with the speed of electrons. If temperature is raised enough, as mentioned before, excitation can also be achieved. Additionally, all objects emit some IR.
Basically, excitation has to do with electron vibrational states (and energy levels), while temperature has to do with the actual speed of electrons through space. Is this more correct?
No. Look up the kinetic theory of gasses. It has nothing to do with "speed of electrons".

I also have a rather uneasy feeling that you think that all light can only be emitted via some transition. That certainly isn't true. Take a clump of charge, ANY charge, and shake it back and forth. You'll get EM radiation there as well! The x-rays that you get in a doctor's office is also not due to any kind of transitions. It is more due to Bremsstrahlung (breaking) radiation.

Zz.
 
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  • #10
No. Look up the kinetic theory of gasses. It has nothing to do with "speed of electrons".

I also have a rather uneasy feeling that you think that all light can only be emitted via some transition. That certainly isn't true. Take a clump of charge, ANY charge, and shake it back and forth. You'll get EM radiation there as well! The x-rays that you get in a doctor's office is also not due to any kind of transitions. It is more due to Bremsstrahlung (breaking) radiation.

Zz.
Ahh so temperature is applies to not only electrons, but whole atoms. I knew this at some point, but in trying to integrate new information it got buried.

Your uneasy feeling was also correct. I read up some on this; I understand a little better but I might still be wrong. EM radiation is associated with accelerating a charge (e.g. an electron). An energy level transition is simply one form of this phenomenon.
Some sources say that simple charge acceleration causes EM radiation:
https://physics.stackexchange.com/q...ing-charges-radiate-electromagnetic-radiation

Others say that it is way more complicated than mere acceleration of charges (I won't pretend that I understand this source; it was an interesting read, though most of it went way over my head):
https://www.mathpages.com/home/kmath528/kmath528.htm

Thanks everyone for the guidance this far :)
 
  • #11
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Well, there are some concepts called "electron temperature" in plasma physics, but I don't think that's relevant to what you are talking about. (The term is also misleading). High temperature means that the atoms are moving around (having high kinetic energy). Within a molecule, then the composing atoms are vibrating.

You intuition that electronic transition of an atom is merely one of the interaction between electron and EM radiation is correct. The interaction between EM radiation and charged particles are well documented in physics. If you are talking purely about one electron and EM radiation, the large picture is that we have two type of charge interactions and one spin interaction. If we take one of the charge interactions and spin interaction, and take the first-order perturbation expansion, we have the single photon absorption/emission interaction. Dipole expansion of this these interaction leads to the electric dipole and magnetic dipole transition if we look at the first-order. Typically, the magnetic dipole transition is much smaller than the electric dipole transition. The electronic transition you are talking about is most likely this electric dipole transition.
 
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  • #12
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Homework Statement:: 1. Does the increase in kinetic energy in (for example) water that results from increasing its temperature result from electron excitation (i.e. increasing electron energy levels) or simply increasing their velocity or vibration amplitude/frequency?
Increasing vibration amplitude IS excitation.
For example water, and many other substances, contain almost no energy in electron excitation and almost all in velocity or amplitude of nuclei. The substances that do have a lot of energy in electron excitation still have a lot in nucleus movements as well.
2. If excitation is involved, does that mean by definition that gases > liquids > solids in terms of the magnitude of excitation?
By which measurement?
Take a piece of frozen quicksilver. It has a lot of energy in the excitations of conduction band electrons and also a lot in the vibrations of quicksilver nuclei frozen in crystal.
Melt it and then evaporate it. Quicksilver vapour has no conduction band, so all electrons are in ground state atoms and no longer have low lying states to excite into. The nuclei have bigger velocity, but they are no longer frozen to vibrate around their lattice positions and therefore no longer quantized into excited states. The excitations are gone.
This leads me to a couple more questions.
1. Do infrared cameras detect humans and animals because of reflected IR, or are some of our atoms excited enough to emit IR?
That depends on what precisely the "infrared" camera is designed to detect.
"Visible light" for 390 to 780 nm is just a ratio of 2. IR is simply everything redder than that up to quite far, to "microwaves" at over 3 000 000 nm. Which is 4000 times difference from 780 nm to 3 000 000 nm.
People have blackbody peak around 10 000 nm. If you build an infrared camera that detects 10 000 nm radiation, it will detect IR emitted by bodies (but also IR reflected by bodies). If you build a camera that detects IR at 800 of 850 nm, then live bodies are nowhere near hot enough to emit that, so the camera will detect reflected IR alone.
 

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