Please, will you explain the nature of spectral lines

[naughtyknight]

Hi,


I was wondering what really ARE spectral lines?
Are they electromagnetic waves?
But still they are affected by magnetic & electric field in the Zeeman and Starks effect respectively, whereas the electromagnetic waves are not. so is there any theory explaining all these things?
Also how did the scientists established the existence of sublevels and orbitals on the mere splitting of spectral lines?

 

[HallsofIvy]

I think you are misunderstanding what you have read. "Spectral lines" show a relatively high intensity of EM for a narrow band of frequencies produced by a given atom. It is the affect of the magnetic and electrical field on the atom producing the wave, not on the wave itself, that changes the spectral line.

 

[naughtyknight]

You mean to say that application of magnetic field or electric field causes the atom to change the spectral lines it had been producing, but it doesn't change the pattern of spectral lines already produced by the atom.

but still how one can establish the existence of sublevels and orbitals on the mere splitting of spectral lines? It may happen that due to the existence of electric/magnetic field the extent of ionisation of various electrons changes differently, depending upon where the electron is located at the particular moment, causing the previously identical lines to split due to different frequencies

 

[malawi_glenn]

Spetcral lines are as HallsofIvy wrote the photons (EM-waves) produced by an atom, each line represents an energy level of electrons in that particular atom (forget about electrons locations etc, we are talking about quantum physics now!)

So spectral lines are the energy distrubution of the atom, the lines we observe are millions of photons, coming from millions of atoms in our samle (e.g gas)

The tiny broadening of these spectral lines are just the manifestation of the energy-time uncertainty relation. Each energy level has a certain lifetime (before it decays into the ground state of the atom) so the longer the lifetime, the sharper (more precise) will that energy level be as a spectral line.

Now when the atom is not in an external magnetic or electric field, the energy levels are degenerate. But since the electrons are tiny tiny magnets, by placing the atom in such field, the energy levels will change and thus more possible spectral lines (energy transitions in the atom) are permitted.

You can learn about this in any introductory book in quantum physics.

 

[Renge Ishyo]

Also how did the scientists established the existence of sublevels and orbitals on the mere splitting of spectral lines?

This was Bohr's contribution. He incorporated at the time "radical" new ideas about quantization (from Plank's quantum explanation of black body radiation) and Einsteins photoelectric effect (E=hv) into a model that could account for the observed line spectrum of a hydrogen atom. Note that the description of the spectral lines came a bit later...the real leap was the idea of quantization itself.

The "splitting" of spectral lines is due to the magnetic effect. For example, if you place an atom in an external magnetic field a given energy level will split into two energy levels (one of lower energy with the field, and one of higher energy against the field). This is called the Zeeman effect. In and of itself this did not contribute to the first few quantum models of the atom, it was added in later after the original models were established.