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Electron Transition Time
Name: Ayed R.
Status: student
Age: 20s
Location: N/A
Country: N/A
Date: 1/13/2003
Question:
What is the time that the electron need to jump from one
energy state to the next energy state?
Replies:
Yours is a very subtle question (or let us say the answer is). Quantum
mechanics tells us a lot about the properties of various energy levels, but
not very much about what happens in between. The lifetime of some excited
states can be measured. They vary from nano seconds to hours. Here is how its
done (simplified)"
Suppose a molecule or atom has three (or more) electronic states: E0, E1,
E2, ... with different energies:
E0 < E1 < E2 < ...
If the sample is exposed to radiation of energy (or
frequency, because E = h*nu, where 'h' = Planck's constant and 'nu' is the
frequency) having an energy equal to E2 - E0 the excited state may decay by
a transition(s) E2 ----> E1 ----> E0 or E2 ----> E0. One then uses a
spectrometer to monitor the intensity vs. time of the cascade of energy
levels (frequencies). This gives you the lifetimes of the various electronic
states.
Now if you mean the transition lifetime, that is, the time it takes for
an electron to go from one energy state to another once it has "decided" to
do so, then "garden variety" quantum mechanics is silent. You might use the
Heisenberg uncertainty principle in the form dE*dt ~ h where dE is the
energy difference, dt is the transition time, and 'h' is Planck's constant,
but this is really a cop-out to avoid the very difficult question of:
"How does the electron behave with the surrounding electric and magnetic
fields "as it moves" from one state to another???" This becomes really
tricky, and not really settled to my knowledge, because what you are asking
is: "What is happening to the wave function's dynamical behavior?" This
question is about: "What is a wave function? What is quantum mechanics? What
is a photon of electromagnetic radiation?" These questions are not settled.
If you want to delve into these questions, I recommend that you read
"Schrdinger's Kittens and the Search for Reality: Solving the Quantum
Mysteries" by John Gribbon. It is readable and he lays bare some really
fundamental questions that relate to your question.
Vince Calder
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