Electronic property that determines optical transparency

[StringJunky]

What electronic property of an atom or molecule determines whether it will be transparent to some wavelength? Is it the outer electronic configuration, which orbital the outer electrons reside in, whether there is a specific pair/combination there, or something else?

Mods: Move it if it's in the wrong place.

E2A: To rephrase: What is it about the outer electron configuration that causes transparency to a/some wavelength/s?

Edited February 13, 2020 by StringJunky

[swansont]

It's basically not having populated states separated by the energy (and thus wavelength) in question. That becomes much harder to do when you have complex molecules than for individual atoms and simple molecules, because of all the states available once you start combining multiple atoms

 

[StringJunky]

12 minutes ago, swansont said:

It's basically not having populated states separated by the energy (and thus wavelength) in question. That becomes much harder to do when you have complex molecules than for individual atoms and simple molecules, because of all the states available once you start combining multiple atoms

 

Thanks. I'll have to reflect on this but is it right to say that the more available states there are, the harder it is for a photon to pass through?

Edited February 13, 2020 by StringJunky

[swansont]

1 hour ago, StringJunky said:

Thanks. I'll have to reflect on this but is it right to say that the more available states there are, the harder it is for a photon to pass through?

Available transitions would be a better way of stating it. (With the caveat that some transitions are "wider" than others, energy-wise)

[StringJunky]

15 minutes ago, swansont said:

Available transitions would be a better way of stating it. (With the caveat that some transitions are "wider" than others, energy-wise)

That's clearer. Thanks.