Can an electron move to a higher energy level on a permanent basis?

[memphisforest]

Hi, I have some very basic questions regarding electron energy levels/states.

In the basic atom model when an electron becomes excited (i.e. absorbs a photon or collides with a nearby atom or particle) and moves into an energy state greater than its ground state, must it always eventually return to the ground state? Or are there circumstances where an electron may remain in this higher energy state on a permanent basis?

Likewise, is it possible for an electron to drop to a lower state (i.e. after emission of a photon) on a permanent basis, or must it always return to its ground state?

Any clarification would be very much appreciated.

 

[mathman]

The simple answer to your question is that there is no mechanism (except by outside intervention) to lock an electron into a particular excited state. Even the ground state is hard to maintain.

 

[memphisforest]

Thanks. I guess what I was trying to ascertain was: Is the return to ground state inevitable? My current understanding is that the ground state is almost a 'default' energy level to which the electron, over a long enough time frame, will always return (unless it escapes the system). Or am I picturing this incorrectly?

Excuse my lack of knowledge - am not a physicist, as you may have guessed...

 

[granpa]

the ground state is the lowest energy state so it will always tend to end up there.

even if it were below the ground state it would be in a higher energy state and would return to the ground state.

 

[math_way]

Hi memphisforest,

The answer to your question, is no. Its impossible for electrons to stay in any single energy state for a long time. (By long time i mean less that 1/1000000000 of a second.) You know that electrons continuously emit radiations of different frequencies or energies. This is due to the fact that they keep switching between different energy states. Though the Ground State is the most stable state for an electron, as Mathman put it well, it is difficult for an electron to stay in its ground state for a long time!

Keep asking questions,

Regards,
math_way

 

[M Quack]

Math_way, where did you get that information? 10^-9 sec is a very short time (1 nano-second). One would expect the ground state of an isolated atom or molecule in good vacuum to be more stable than that.

The same topic was already discussed here:

https://www.physicsforums.com/showthread.php?t=360664

Transitions to intermediate, metastable states are the basis of all lasers. The article below claims lifetimes of micro- to milliseconds.

http://www.rp-photonics.com/metastable_states.html

 

[cmb]

I don't believe what has been said in this thread.

As far as my simplistic, 'classic' understanding goes, electrons require energy input to change orbital. That energy can't come from simply nowhere. Similarly, an electron in a higher orbital exposed to EM will drop down if exposed to further radiation of a similar wavelength as the transition represents.

 

[mathman]

I don't believe what has been said in this thread.

As far as my simplistic, 'classic' understanding goes, electrons require energy input to change orbital. That energy can't come from simply nowhere. Similarly, an electron in a higher orbital exposed to EM will drop down if exposed to further radiation of a similar wavelength as the transition represents.

An electron in a higher energy state can simply emit a photon and drop down (spontaneous emission) or can be stimulated by a photon of the same wavelength as the transition (stimulated emission - the basic principle of lasers).

 

[cmb]

[]

EDITED/Deleted... sorry, wrongly attributed a statement to mathman instead of math_way

 

[cmb]

An electron in a higher energy state can simply emit a photon and drop down (spontaneous emission) or can be stimulated by a photon of the same wavelength as the transition (stimulated emission - the basic principle of lasers).

Sorry, I did not mean to imply otherwise [that a spontaneous emission could not occur].

I don't know enough about quantum physics to judge if it 'simply' emits a photon, or comment on when/how quick and excited electron 'chooses' to return to a lower state without external stimulus.

 

[M Quack]

The most important factor is the transition dipole moment, i.e. the matrix element of the electric dipole operator between the initial and final states. If that is zero, then the transition is "forbidden", i.e. the transition has occur in higher multipolar order, the matrix element is much smaller, and thus the lifetime is much longer.

http://en.wikipedia.org/wiki/Spontaneous_emission

http://en.wikipedia.org/wiki/Transition_dipole_moment

 

[Naty1]

electrons require energy input to change orbital. That energy can't come from simply nowhere.

Sure it can:
Quantum mechanics, in fact, guarantees 'energy from no where'.

 

[cmb]

Sure it can:
Quantum mechanics, in fact, guarantees 'energy from no where'.

OK, so, how often? Are you going to go along with math_way at once every nanosecond per atom?!

 

[math_way]

Hi,

See, transition taking place once every nanosecond, is just a very rough estimate. It might infact take even lesser time, before a transition takes place, or even greater amount of time. The problem really is that in quantum mechanics, there can be energy energy changes at any pt in time, thereby triggering a transition. Hence transitions can take place at any point in time, and maybe in even less than a nanosecond.

https://www.physicsforums.com/showthread.php?t=75192

regards,
math_way

 

[chill_factor]

Hi memphisforest,

The answer to your question, is no. Its impossible for electrons to stay in any single energy state for a long time. (By long time i mean less that 1/1000000000 of a second.) You know that electrons continuously emit radiations of different frequencies or energies. This is due to the fact that they keep switching between different energy states. Though the Ground State is the most stable state for an electron, as Mathman put it well, it is difficult for an electron to stay in its ground state for a long time!

Keep asking questions,

Regards,
math_way

i think this is incorrect, correct me if I am wrong but very rarely is there enough energy to excite a core electron to a non-ground state due to not only the immense energies involved in the n=1 to n=2 transition (tens to thousands of eV) but also the Pauli exclusion principle forbids inner electrons in most multielectron atoms from jumping to the lowest avaliable non-ground states. the potential well to escape is very very large.

for OP, the electron will spontaneously fall back down because the high energy state is an unstable equilibrium and even the tinest perturbation will make it fall back down to the lower states. it might not directly fall down to the absolute ground state though; it could first lose energy through internal conversion and then radiate, which causes fluorescence.

 

[cmb]

See, transition taking place once every nanosecond, is just a very rough estimate. It might infact take even lesser time, before a transition takes place, or even greater amount of time. The problem really is that in quantum mechanics, there can be energy energy changes at any pt in time, thereby triggering a transition. Hence transitions can take place at any point in time, and maybe in even less than a nanosecond.

And would these transitions release EM radiation, or otherwise what are the conditions when EM is release, and when is it not released?

Would you agree that EM is released and radiates when an electron undergoes a drop to a lower excitation state?

 

[chill_factor]

And would these transitions release EM radiation, or otherwise what are the conditions when EM is release, and when is it not released?

Would you agree that EM is released and radiates when an electron undergoes a drop to a lower excitation state?

all atoms and molecules have not only electronic energy levels but also vibrational and rotational energy levels superimposed on them. an atom can undergo a drop from one vibrational level to another in the same electronic energy state and release no radiation; this is called internal conversion. the excess energy is released as heat. of course then it will indeed drop down later to the ground state, but the EM radiation would be a lower frequency.

 

[cmb]

It's a specific question for math_way. What he is saying does not add up, so I just want to probe his understanding of this.

 

[math_way]

>>@cmb


okay cmb, now put forward your question. My answer to the original question: Can an electron move to a higher energy level on a permanent basis?, is no. Its impossible to stay at a higher energy level permanently, given that:

1) Electrons are most stable in their ground state
2) And transitions can take place at any time, which means, it again is impossible for an electron, to stay in the same energy level, for a long time.

These two are very basic assumptions. (High School Physics)

I agree i got a bit off the topic, and started talking too much about transitions, but anyway go ahead and question me, if you really want to probe my knowledge on this topic. And go on, oppose me if you feel i am wrong

regards,
math_way

 

[cmb]

I want you to clarify what you mean by suggesting electrons are constantly, and rapidly, bouncing up and down in their orbits. Why would this process not be emitting copious EM emissions?

I think you have confused 'quantum fluctuations' with 'electron orbit' changes. I do not have background on quantum stuff, but even my classic knowledge says this is wrong. If an electron were to be in a metastable higher orbit then, yeah sure, constant quantum fluctuations may be at work to dislodge it from its orbit and send it hurtling back to its ground state.

But I do not, at all, see that quantum fluctuations are capable of dislodging a ground state electron and shifting it up to a higher orbital, except in extremely rare statistically anomalous events (as in - once per mega year, or whatever..).

So I want you to think about whether you've wrongly conflated quantum fluctuations with electron orbital changes.

 

[math_way]

I want you to clarify what you mean by suggesting electrons are constantly, and rapidly, bouncing up and down in their orbits. Why would this process not be emitting copious EM emissions?

I think you have confused 'quantum fluctuations' with 'electron orbit' changes. I do not have background on quantum stuff, but even my classic knowledge says this is wrong. If an electron were to be in a metastable higher orbit then, yeah sure, constant quantum fluctuations may be at work to dislodge it from its orbit and send it hurtling back to its ground state.

But I do not, at all, see that quantum fluctuations are capable of dislodging a ground state electron and shifting it up to a higher orbital, except in extremely rare statistically anomalous events (as in - once per mega year, or whatever..).

>>@cmb

Right! That makes sense. What you are saying is perfectly right, when the atom is isolated. There will be quantum fluctuations, that will not cause a higher transition.

But that is'nt really the case, right? there is always some external energy acting on the atom, that could excite the electrons, which could move the electron from a lower state to a higher state.

I considered a case, where the atom is not isolated. Hence I went on to say that there will be higher level transitions(Energy acts on atom). And similarly, loss of energy (as EMRs) could bring down the electron... So it all just depends on how you look at it!:)

 

[cmb]

I considered a case, where the atom is not isolated. Hence I went on to say that there will be higher level transitions(Energy acts on atom). And similarly, loss of energy (as EMRs) could bring down the electron... So it all just depends on how you look at it!:)

So, if we consider a hydrogen atom, then the smallest energy band drop to ground state is ~2eV. Are you saying that we should be seeing a constant emission of EM radiation, with 2eV energy, because these electrons will keep bouncing up to that orbital, then dropping down again?

 

[math_way]

So, if we consider a hydrogen atom, then the smallest energy band drop to ground state is ~2eV. Are you saying that we should be seeing a constant emission of EM radiation, with 2eV energy, because these electrons will keep bouncing up to that orbital, then dropping down again?

No. (Lymann series - From n=2 to ground state(n=1)) We will not be able to see a constant emission of 2eV, but that's because there is energy both being absorbed and emitted(considering the atom is not isolated) and this amt of energy that is released/absorbed varies again according your transition(its diff for n=2 to n=0,n=3 to n=0,etc.) There are others factors, like quantum fluctuations, etc. that affect the energy released/absorbed.

Let's consider a situation:

There is an atom, having just 1 electron(say Hydrogen). Now the electron is isolated, which means there is no energy acting on it. Now if the electron jumps from the highest state to the ground state, we will have an EMR emitted. Now once the electron has made it to the ground state, if there is no external energy acting on it, it must remain in its same state forever. But according to the fundamentals of Quantum Physics, Energy can come from NOWHERE. Hence the electron can switch shells.


here's an article, that supports this idea of "ENERGY FROM NOWHERE". It even addresses the question of creation of the universe:

http://www.infidels.org/library/modern/mark_vuletic/vacuum.html

In Conclusion, the concepts of Classical Physics alone cannot alone be used to explain this concept, but application of Quantum Mechanics is required, to explain it.

The problem cmb, is that you are restricting youself to Classical Mechanics. Go on and explore Quantum Mechanics, you'll find an answer to this problem.

Anyway, after the above discussion its obvious that the energy emitted can not be a constant, when rules of quantum mech is applied.

 

[cmb]

No. (Lymann series - From n=2 to ground state(n=1)) We will not be able to see a constant emission of 2eV, but that's because there is energy both being absorbed and emitted(considering the atom is not isolated)

Can you clarify/qualify 'isolated system'? If I have one atom, can it absorb its own emissions? If I have more than one atom, how many atoms do I need to guarantee re-absorption of this EM energy?

 

[math_way]

Can you clarify/qualify 'isolated system'?

>>@cmb

Now, an "isolated system", here, means there is no EXTERNAL application of ENRGY on the atom.

If I have one atom, can it absorb its own emissions?

According to my understanding, the answer to this is yes(paritally). But an atom cannot absorb all of the energy, it emits. Hence, while majority of the energy is emitted, there is some energy that is being re-absorbed. This absorbed energy, in my opinion can be used by the atom.

If I have more than one atom, how many atoms do I need to guarantee re-absorption of this EM energy?

Well, when one atom is enough, I think any number of atoms should'nt be a problem

 

[cmb]

But an atom cannot absorb all of the energy, it emits. Hence, while majority of the energy is emitted, there is some energy that is being re-absorbed. This absorbed energy, in my opinion can be used by the atom.

How much of the energy is not reabsorbed?

 

[math_way]

Not sure. The answer will be a variable, and my assumption is that a MAJOR part of the energy is not re-absorbed .

 

[cmb]

Not sure. The answer will be a variable, and my assumption is that a MAJOR part of the energy is not re-absorbed .

OK, so the corollary of what you've said is that a minimum of 1eV per nanosecond (this is a half of the smallest electron transition to ground) is being lost, per hydrogen atom, from quantum fluctuations?