Why are molecular spectra more complex than atomic spectra?

[mystery_witch]

I'm studying astronomy and I'm have these problems to solve, but there are a few things I don't really understand, hopefully someone can explain these things to me.

1. Why are spectra of molecules more complex than spectra of atoms? Is it because molecules can be excited in different ways?

2. Molecular band, what exactly is it? Is a group of lines in a spectra of a molecule?

 

[Gokul43201]

Have you looked at the problem of the rotational/vibrational spectrum of a diatomic molecule? You need to start here (or even first, with the rigid rotor problem). When you do this, the answers to both questions above will become evident.