Question about Radiationless De-Excitation

[Kavi]

Hello,

I understand that an electron in an atom can:

1. Absorb any amount of energy from a photon and become excited
2. It may move to a higher energy orbit or remain in the current orbit
3. To move to a lower energy orbit, it must release excess energy so it is at the ground level of the current orbit (Radiationless Deexcitation)
4. Moving to a lower orbit, it will release a photon with properties dependent on the structure of the atom.

If the above is correct, I want to ask,

The mechanism for 3. above is Radiationless Deexcitation. I wanted to know more about this.

Specifically, why does this happen at other excitation energy levels but not at ground energy levels for any given orbit?

 

[DrClaude]

I don't understand what

it must release excess energy so it is at the ground level of the current orbit

means.

The state of the electron is quantized, meaning that it can only exists in certain discrete states of energy. To change state, it must receive or give away energy, which is most often through interaction with the electromagnetic field (absorption/emission of photons). But it can also exchange energy through other means, such as collisions. This is how you could have radiation less de-excitation. But the electron cannot lose energy this way "by itself."

 

[sophiecentaur]

@Kavi
Describing the structure of an atom in terms of “orbits” is very old fashioned. It fails because there are many other energy states of all but the Hydrogen atom where that simple mechanical model doesn’t work.

In any case, any interaction between charged particles is best described in terms of a photon exchange. Afaik there’s no other magic way for energy to get around in the low energy world of atoms and molecules

 

[Kavi]

Thanks guys, the responses helped, and I did some more researching and found what I was looking for.

Basically, what I meant to ask for was the difference between the emission spectrum and the absorption spectrum, but I didnt know to frame the question in those terms.

If I understand this correctly now, then there is some little difference between the two spectrums and they are not pure inversions of each other, the emission spectrum contains wider frequencies than those of the absorption spectrum.

 

[sophiecentaur]

the difference between the emission spectrum and the absorption spectrum,

You were asking about 'point 3'. if the energy is all internal then there will be no emission or absorption.

the emission spectrum contains wider frequencies than those of the absorption spectrum.

When we observe absorption spectra, the radiation is often re-radiated but in other directions. hence the apparent dip at certain characteristic frequencies. Other frequencies can cause internal changes which may be permanent or semi permanent.

 

[Kavi]

You were asking about 'point 3'. if the energy is all internal then there will be no emission or absorption.

When we observe absorption spectra, the radiation is often re-radiated but in other directions. hence the apparent dip at certain characteristic frequencies. Other frequencies can cause internal changes which may be permanent or semi permanent.

Hi, thanks for that. I found the below explanation on another site but I am not sure if it is exactly correct?

In the emission spectrum, the electrons in the energy levels usually start at random energy levels and so there is more of a variety of wavelengths that could possibly be emitted.

Whereas in the absorption spectrum, there are a few lines missing because most electrons start from ground state, meaning that there are less options of energies that a photon can be emitted at.

https://physics.stackexchange.com/q...ion-spectrum-than-on-the-emission-spectr?rq=1

 

[sophiecentaur]

Hi, thanks for that. I found the below explanation on another site but I am not sure if it is exactly correct?
https://physics.stackexchange.com/q...ion-spectrum-than-on-the-emission-spectr?rq=1

This is more of an observation than an explanation. I would put it this way:

Emission spectra are generated in regions where there are 'high energy' conditions, with fast electrons around (for instance). Temperatures can be high and so there will be significant numbers of atoms in higher states than the ground state or even ionised.

"Random states" would only occur in very extreme conditions of pressure and temperatures where the energy states are spread (line broadening - look up Pauli Exclusion Principle). But I don't think this applies here: states are not Random or blurred but discrete. The phrasing should be "more possible states".

Absorption spectra are seen in cold regions of gas where most atoms are in the ground state. But the absorbed (star) light will be re-emitted in other directions over the whole sphere. The spectrum of this light will tend to be a single line.