Atomic spectra: why?

[fafalone]

We can look at an element's spectral pattern, and know what it is. Everything has its own spectrum that we observe; but I wonder, why does a particular element have a particular spectrum? What determines that pattern? I don't understand how it could simply be the mass; since there's a much wider variety of colors than types of particles.

[Radical Edward]

it is a combination of factors, such as the energy levels, spins and so on of the electrons, as well as the charges and mass of the nucleus, and also splitting due to the different quantum numbers and field interactions allowing certain transitions between energy levels, but not others. In essence, it's quantum mechanics.

[fafalone]

BUt how specifically does this translate into the wavelength of emitted photons?

[Radical Edward]

if we consider an atom, there are a number of energy levels that the electron can occupy, and transtions between these different levels emit at different wavelengths. the energy level itself is affected by a number of factors, such as the charge of the nucleus, the distance of the electron from the nucleus (more because there may be other electrons shielding some of the charge) There are aditional complexities, such as splitting of levels in a magnetic field - the sodium doublet, and hyperfine splitting.

[fafalone]

I understand the components that make it up; but how can I take all those values and find the resulting wavelength? Equations?

[JaKiri]

Originally posted by fafalone

I understand the components that make it up; but how can I take all those values and find the resulting wavelength? Equations?

 

E = hf. E being the energy of the wave, h being Planck's constant (6.6x10^-34 Js) and f being frequency.

 

Of course, it may be E = hc/f, but my mind isn't working as I've only just woken up.

[fafalone]

I know that.

 

But that doesn't explain how all the components make that equation true.

[Ozman]

As far as using quantum mechanics (or any other well developed theory) to define the nature of an atom, i.e. to arrive at the radiation (and its frequency) emitted by an atom, or to predict the same for a group of atoms? Yeah, somebody other than myself can come up with a mathematical solution based on quantum mechanics theory or a half a dozen more obscure theories. The bottom line is this: the radiatied energy emitted by matter is at one or more of the resonant frequencies of that atom. Many competent public school physics teachers have a good enough grasp of the concept to convey it to students who are of at least have average intelligence and an interest ( I know, that seems like a huge stretch) using a one atom hydrogen model. The more complex the atom, the more complex the math, but, in general, also the more possibilities/probabilities of resonant frequencies.

More matter, that is a greater quantity of atoms, means more complex reonance, a different (net) resonant frequency, sometimes described as a beat frequency. Multiple resonant frequencies in a single atom model need not be and generally are not harmonics of one another. As a body of matter becomes more extensive and / or other types of atoms, either isotopes or different elements begin to interact, quantum mechanics and pretty much all the other mathematical mechanics become effectively unmanagable for a human or even a team. That's why they invented the Cray Supercomputer and its ilk, to calculate such complex operations as predicting the exact interaction of all the subatomic particles contained in a cubic millimeter or so of hydrogen (actually I think it was dueterium) at atmospheric pressure, a few hundred atoms. A Cray supercomputer could crunch those numbers in a matter of days instead of the decades it would take a decent-sized team of mathematicians with caulculators.

 

Now I segue right into...

 

Astonomers look at the emitted energies from a star and try to determine the elemental nature of the source (with apparent success). But they observe star-sized objects, incredible, incalcuable numbers of atoms. The astronomers observe the net effect and make educated, considered conclusions as to what makes up "star stuff" based on observations of emissions from certain elements on Earth.

This begs the question: how sure are we that the spectral data gathered on Earth is truly the lynchpin of effectively studying stellar spectra?

[Radical Edward]

equations? there are an awful lot of them... there are also additional complexities due to pauli exclusion principle and so on.. I did a three month course on atomic physics, and we barely scratched the surface of it, proving the spectra of only a couple of elements, hydrogen and helium.

[Ozman]

Thanks, Rad Ed, I feel validated.

Any theory that would adequately describe all the matter energy relationships in a body as complex as a star would be beyond human comprehension. I think that's why I'm not a scientist.

Little bits and pieces at a time (single atom chunks) can be explained to the point of accepting a theory.

 

But that still doesn't answer my question: How confident are we that the spectral data of an element gathered on Earth is applicable to the study of stellar spectra? If "we" are completely confident, and unwilling to entertain the possibility of there being a disconnect between the two, then doesn't that fly in the face of scientific method?

[fafalone]

Hydrogen is hydrogen, the there aren't differences between the hydrogen atoms here on earth and the ones we've collected from asteroids that have impacted us; so why would its spectral pattern be different just because it's farther away? (I'm not saying it's entirely impossible, but I can't imagine a reason besides equipment error)

[Ozman]

Here's where I'm going with that question. Yes, hydrogen or any other element has its own distinctive spectral emission. We can repeatedly demonstrate the effects and even turn them to useful purposes. But when we look at stars, we are not looking a a single atom or a single element. We are looking at (observing for puposes of research) a very complex and dynamic system of matter and energy. We then compare the emissions of that star to the emissions of very simple models and reach a conclusion, write it down, and submit it for scientific review.

Has noone ever questioned that there may be beat frequencies or other phenomena that would give the same appearance as it being a giant puddle of excited gases?

 

Please don't misinterpret; I'm not disagreeing with the generally accepted theories. I'm just confused that we rarely are willing to readily entertain alternative theories once a conclusion has been reached by one researcher and others concur in a refereed debate.

 

Posit:

Is it even possible that two elements with distinct and different spectra could, as a system, produce a third set of spectra because of the interactions of the originals?

Yes, I'm asking about wave and/or particle interaction to produce a sympathetic/ constructive interference situation.

I'm not asking this in terms of free space mixing, but in the middle--actually, at the surface-- of star stuff.???

[Radical Edward]

Ozman : I see what you're asking, and roughly speaking, you are right, a body as complex as a star does alter the spectra of the emissions, however, this is in fact a good thing:

 

such things as magnetic fields and even pressure will change the pure spectra of an element, and by looking at the differences between the raw spectar and the adjsuted one, we can see the conditions inside the star - this is one method that can be used to test the overall properties of the star itself.

Furthermore, when we consider more complex elements, and arrangements of elements, such as crystalline silicon, it is this variation in the energy levels of the atoms that actually give the material it's properties, giving energy bands, with much larger linewidths instead of the narrow spectral widths of a pure element.

[Ozman]

Thanks Rad Ed.

I think what you just described is "band gap" phenomena. Something that the folks out at Sandia are pursuing with diligence for practical, planetbound applications.

And you hit on the effects of magnetic fields possibly altering spectral emissions. And you mentioned silicon.

 

So here we go...

 

I have long held the hypothesis that a physically small, very intense magnetic field constructed (artificially) around the emitter face of a quantum well or quantum dot laser (becaus

e physical size, i.e. proximity, is a limiting factor) would provide a means of "tuning" the emitted energy. The math says, or appears to say, that it will (somebody besides me needs to run the numbers--I don't always agree, even with myself. My mathematical prowess falls off dramatically with anything more complex than simple trig).

 

Constructing an effiecient or even comparatively effective tori around the face of the emitter is in the realm of nanotechnology and something I can not pursue. But I would certainly encourage somebody with the means to do so.

 

Does it happen in stellar bodies? You and I seem to agree that it may.

 

(Yes, it was a leading question. Sorry)

 

Not to pick nits, but you didn't get all of my question or I didn't articulate it well.

 

In a complex system, does the interaction of the particles produce a spectra that is distinct and seperate from the elemental spectra? I don't necessarily mean light in the traditional sense. Obviously, if there is mass, there is attraction and/or repulsion. If magnetic fields affecting the body are intense, then that alters the equation, even if it is only by a minute factor. Does the gravitational field have a similar (or even dissimilar) affect and if so, would that be a possible cause of red shift?

(I know, that should be in the cosmology section and I will probably paste it into the Big Bang thread).

[Radical Edward]

I'll just answer the complex system bit for now: yes it does, there are a number of effects that may occur, for example the emission patterns of molecules are much different to the emission patterns of lone atoms, as some of the electrons are tied up in atomic bonds etc. usually the emissions from molecular bonds are very broad band, and not close to the emissions that would exist in the atoms on their own. these emissions come from extra degrees of freedom that exist within the molecule, such as rotational and vibrational modes, which carry their own characteristic excitation energies. furthermore you can get exiplex interactions as well, between excited states of atoms (and molecules) with further add to the mix of complexity, as can be seen in Noble gas lasers such as KrFl lasers.

[Ozman]

Okay, I still didn't articulate it well enough.

 

I know enough to be dangerous regarding rotational and vibrational molecular spectra (from work with CO2 and and other gas lasers). But I am speculating that there may be interaction between atoms or sub-atomic particles that does not take place in the form of electron exchange, i.e., I'm not asking about molecular spectra. Are there "stresses" that manifest when an atom gets close to another one? Atomic energy / weapon devices run the gamut of known and understood EM spectrum and appear to operate in the predicted fashion. Is there more?

Could there be a "non-EM energy" (for lack of a more precise term) that is emitted because of proximity? Or one that always exists, but only manifests itself in proximity of another atom? We wouldn't be able to detect it directly (like tachyons), but, like neutrinos, we may be able to detect and measure the secondary effects.

 

Or (and this is a real stretch) maybe the spectra we see IS the beat frequency, the difference in frequency between two much higher emitted frequencies. And, although it is a stretch, that may lead to an explanation of the single photon-dual slit phenomenon.

 

Perhaps light is merely the wake formed by by the passage of something else. Something moving much faster.