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

by memphisforest
Tags: basis, electron, energy, permanent
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memphisforest
#1
Mar7-12, 02:52 PM
P: 2
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.
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mathman
#2
Mar7-12, 03:07 PM
Sci Advisor
P: 6,115
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
#3
Mar7-12, 05:06 PM
P: 2
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
#4
Mar8-12, 12:35 AM
P: 2,258
Can an electron move to a higher energy level on a permanent basis?

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
#5
Mar8-12, 01:00 AM
P: 21
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
#6
Mar8-12, 02:05 AM
P: 675
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:

http://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
#7
Mar8-12, 02:29 AM
P: 628
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
#8
Mar8-12, 03:31 PM
Sci Advisor
P: 6,115
Quote Quote by cmb View Post
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
#9
Mar8-12, 03:58 PM
P: 628
[]

EDITED/Deleted... sorry, wrongly attributed a statement to mathman instead of math_way
cmb
#10
Mar8-12, 04:02 PM
P: 628
Quote Quote by mathman View Post
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
#11
Mar9-12, 02:27 AM
P: 675
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
#12
Mar9-12, 01:44 PM
P: 5,632
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
#13
Mar9-12, 02:02 PM
P: 628
Quote Quote by Naty1 View Post
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
#14
Mar9-12, 10:46 PM
P: 21
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.

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

regards,
math_way
chill_factor
#15
Mar9-12, 11:32 PM
P: 900
Quote Quote by math_way View Post
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 im 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
#16
Mar10-12, 01:36 AM
P: 628
Quote Quote by math_way View Post
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
#17
Mar10-12, 01:40 AM
P: 900
Quote Quote by cmb View Post
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
#18
Mar10-12, 02:18 AM
P: 628
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.


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