Why is molecular absorption of radiant energy more complex than that of atoms?

Answer 1

The simple (and correct) answer to why molecular absorption of radiant energy is more complex than that of atoms is rooted in the fact that there are more possible allowable energy levelsfor electrons to occupy in a molecule than an atom. Let's look at those persnickety electrons and see what's up.

In an atom, there are "some" electrons, and they occupy various energy levels. Because of the nature of atomic structure and the behavior of the electron, these electrons have the "opportunity" to move to higher energy levels if they gain extra energy to do so. But it is very important to note that the electrons can move only to specific energy levels dictated by the atomic and the electron structure in a given atom. It's not a free for all. Now focus on the fact that the electrons can only move if they have the exact amount of energy necessary to get to another higher allowable energy level. That quanta of energy must be "just right" for the electron to respond, "grab" the energy, and change energy levels. And, as stated, there are specific allowable energy levels for the electrons in a given atom. But it's different for molecules.

A molecule is made up of atoms, and the atoms bring with them their own allowable energy levels. That does not necessarily mean that a given possible energy level in a given atom is possible in a molecule with that atom in it. This is due to "restrictions" placed on electrons because of chemical bonding and the behavior of electrons of atoms which are bonded. But the presence of two or more atoms in a molecule will "open the door" to more allowable energy levels for the electrons of the atoms in that molecule. And the greater number of allowable energy levels can only be seen in the molecule, and cannot be seen in the sum of the individual allowable energy levels in the constituent atoms.

Answer 2

compounds are made up of more than one element.

Therefore, a compound will have the combined spectra of all of the elements in the compound.

But... the spectrum of the compound is no more complicated than the sum of the spectra of the individual elements. So the actual answer to your question is "It doesn't."

The question I think that you're asking is "Why does a compound have a more complicated spectrum than an element?"

Answer 3

Because they are heavier than atoms so they create more complex spectral lines