Do photons influence the leap of an electron?

[MirceaKitsune]

It's often science documentaries that give me new ideas or offer information on existing ones. Same with an awesome series about spacetime, which recently mentioned something I didn't know about although it didn't elaborate much on. Best idea felt to ask.

 

From what I knew, the leap of an electron into different orbits happens at a constant or random rate. In other words, no interference (at least known to people) typically triggers an electron to "appear" in another location... it just happens based on probability. I did hear that "electrons borrow energy from their surroundings and give it back later", but that still means no known event triggers the leap itself.

 

A documentary about light however said that particles of light (photons) might be a cause for this. If I remember right, the idea was that photons bumping into an electron pushes it into another state. When it comes back from that state, that electron produces a burst of light or energy. It said very little on this matter, but the idea still intrigued me.

 

Is there more known about this? When does a light particle hitting an electron cause it to change orbit / state? Does this mean that particles in completely dark areas show less or no behavior by quantum laws? Is it a rule that two particles need to collide for one or both of them to change location?

[Sensei]

I am not sure what is your knowledge, so will suggest reading about absorption and spectral lines for beginning.
http://en.wikipedia.org/wiki/Spectral_line
http://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)

This video should be also useful for showing different photon-electron-nucleus interactions:

https://www.youtube.com/watch?v=4p47RBPiOCo

[MirceaKitsune]

Thank you, that is helpful. Yeah spectral lines were the topic when this was mentioned. I can better see how photons interact with protons / neutrons / electrons now, but I'm still curious how and when it affects / triggers a quantum leap for a particle too.

[Sensei]

There is no single answer.

 

For Hydrogen you can calculate energy of emitted or absorbed photon with some level of precision.

 

You might want to read about Rydberg formula

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

 

Personally, I like to use this formula

 

E = 13.6/n^2 - 13.6/m^2 (in electron volts)

n >= 1

m >= 2

 

so f.e. for n=1 and m=2

E=13.6/1-13.6/4 = 10.2 eV

 

E=h*c/wavelength

so

wavelength = h*c/E

so

wavelength = 4.135667e-15*299792458/10.2 = 1.2155e-7 m = 121 nm

 

You can put this formula in OpenOffice Spreadsheet, and you will receive something like this:

 

 

[ajb]

There is the process of stimulated emission, where an excited atomic electron interacts with a photon of a specific frequency and drops to a lower energy level while transferring its energy to that photon.

The other process is spontaneous emission which is random and independent of any background electromagnetic fields.

[swansont]

What ajb explains (along with absorption) was described by Einstein in 1916. It's the basis of spectroscopy and lasers, among other things.

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

 

Photon absorption and causing ionization, the photoelectric effect, was explained by Albert in 1905.

[Enthalpy]

Electron into orbit is still a widespread concept, but it's superseded, and misleading. That was Bohr's model of the atom, at a time people still imagined particles as points on definite paths like planets. This model explained much, but not why the orbits were stable, and is abandoned now.

 

Since Quantum Mechanics and Schrödinger, particles are waves. Electrons bound to a nucleus are orbitals or weighed sums of orbitals. The orbitals are immobile, or time-independent, or steady-states; for being immobile, they don't radiate light. The other bound electrons, or weighed sums of several orbitals, do move. They wobble at a frequency proportional to the difference of energy between the orbitals. As the charged electron wobbles, it emits or absorbs light.

 

So you don't have to search for a detailed process where the point electron would "jump" from one orbital to an other. When the electron changes its shape from one orbital to an other, the intermediate shapes wobble and absorb or emit light.

 

Other events can change the shape of an electron, like a collision with an other atom, an interaction with a nearby electron...

 

"Completely dark" is subtle. On Earth without cooling, the surroundings wouldn't be much colder than 300K, so the atom receives permanently photons around 10µm wavelength. These aren't energetic enough for most orbital changes, but enough to change the rotation of molecules. In cold places you still have the 3K background radiation. Artificial cooling achieves colder temperatures. Then you have photons filling vacuum, which make the link between stimulated emission (laser) and spontaneous emission, which is numerically an emission stimulated by these minimum photons.

 

The rate (or rather the mean delay) at which an atom absorbs a well-tuned photon is proportional to the power density of the light, which is the number of hotons per area and time units. The emission rate increases when well-tuned photons are already present (laser), but not only. A reflecting cavity accelerates the emission even if the emitting atom is alone; as opposed, a detuned cavity can slow down the emission.

 

And yes, a change of state means that the atom changes its energy, or angular momentum, or magnetic momentum (often several of them), or other quantities that are conserved, so this means that an other object (for instance a photon) takes the difference with it.