how does spectroscopy work?


Please enlighten me if you will.

Thank you 🙂

In: 2

Every atom is made up of smaller particles: electrons, neutrons, and protons. Every element is made up from a unique combination of these particles.

When an element absorbs “energy”, say from absorbing a beam of light, the electrons get moved around, in a way having moved-around-electrons is what this “energy” is. But those electrons don’t want to stay moved, they hate it, they want to shift back to their starting places. When they do this, they release back out a new beam of light. The “color” of the light released is related to how far the electron moved.

Since we know that every element has a unique set of electrons in unique places AND we know that the “color” of the light released when the electrons move around in these unique places; if we look at the color of light that an atom releases we can tie that all back to the element the atom belongs to.

So for example if I have a sample of gas and I want to know what the gas is I can put it into a spectroscopy machine that examine the light coming off the gas and say it’s carbon and oxygen atoms. A similar machine can count the light and say not only is it carbon and oxygen, there is twice as much oxygen as carbon present. Hence, it must be carbon dioxide.

We can use spectroscopy to determine the elements in a sample of something here on earth, and also use to look at the light coming off a star or a planet and know what elements are present in the star or planet’s atmosphere.

In ELI5 terms, electrons in an atom have orbitals, and these orbitals have specific energy levels; it takes a very precise amount of energy for an electron to move from one orbital to another. So when atoms are subjected to external energy (heat, light), their electrons will absorb some of it and jump to higher orbitals. They’ll spin around for a while, then return to their normal orbitals, releasing energy in the form of photons.

Because the orbitals have very precise energy levels, the photons that are created have very specific wavelengths (colors). The energy of a photon is in its wavelength (color).

So a spectroscope can separate the colors in a beam of light that’s coming from a material, and see [something like this](, making it possible to identify hydrogen vs. iron vs. whatever other element. It’s possible to identify the elements / chemicals in a material, by just looking at the light that’s absorbed, or emitted.

For astronomy, it goes a step beyond, because the speed of the star can [shift the colors]( towards red or towards blue, due to the Doppler effect on light. So astronomers can tell not just [what elements]( are in the star, but also whether it’s moving away or towards us.

Stuff is made up of atoms. These atoms are a bit like mini solar systems, with a nucleus at the centre (like the sun) and electrons orbiting (like planets) at different distances.

But there are specific distances that the atoms are “allowed” to orbit at. Sometimes they jump from one orbit to another, and they release a tiny burst of light – called a photon. The specific colour of light they give off depends on the distance between the level they jump from and to.

The thing is, the allowed orbit distances for an atom depend on the type of atom, the element. This means there are different possible jumps (transitions) for different elements, so different elements will produce different colours of light. It’s a bit like a fingerprint.

So, by looking at the light that comes from something, by splitting it up into a spectrum (using a prism), we can see what specific colours they are and how intense they are. We can then compare this to the fingerprints of each element, and work out what elements make up the thing giving off the light and in what quantities.