What is meant when it is said that a molecule is excited?

In summary, an excited molecule is one that has its electron excited to a higher energy state. This can be done by light or other forms of radiation, and is used for various spectroscopic techniques.
  • #1
Ahmed Abdullah
203
3
I know what an exited atom is : any of it's electron is elevated from the ground state. But I can't really figure out what is an excited molecule (e.g diene of polyene)...
I have read molecules like diene or polyene can be excited and they absorb light wave for this as atoms do to send some of their electrons to higher energy level.
Is it something like , hmm...the molecular orbital is enlarged so that the shared electrons can enjoy extra freedom (higher energy) or something else?
I think you have understood the problem.
 
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  • #2
Well, exciting a molecule is pretty much the same concept as exciting an atom. It just gets a little more complicated when you do it to electrons in bonds, or to non-bonded electrons on an atom bonded to other atoms.

The electrons in molecule bonds have excitation states they can be pushed into by the absorption of light just like non-bonded electrons. Of course, this leads to anti-bonding orbitals and such, as well as the concept of chromophores, organic molecules that absorb in the visible to ultraviolet spectrum.

So it's technically not the molecule, but the electrons within the molecule that are excited, just like with atoms I suppose.

Which, that absorption and the re-emission are taken advantage of for all kinds of molecular absorption spectrometry.
 
  • #3
Ahmed Abdullah said:
I know what an exited atom is : any of it's electron is elevated from the ground state. But I can't really figure out what is an excited molecule

A molecule can exist in many many states. One of these is the ground state. If the molecule is in any other state than the ground state, it is said to be in an excited state or, simply, excited.

Because a molecule consists of more than one atom, it has more degrees of freedom than a single atom: a molecule can rotate and vibrate. If you shine microwave radiation of the correct frequency on a molecule, it can be rotationally excited. Infra-red radiation excites the vibrational modes. Much higher frequencies (visible light, ultraviolet light) may excite the molecule into a higher electronic state.
 
  • #4
Feh, shouldn't have typed my first post out just after waking up from a nap, as it came out ambiguous and confusing sounding, to me at least.

As pkleinod pointed out, there are different ways a atoms (and by extension molecules) can be excited. Visible light and higher frequencies have an effect on the electrons themselves, pushing them into higher states. Infrared causes the whole molecule to vibrate, and microwave and lower frequency radiation causes the molecule/atoms to spin (which can be prohibited by molecular bonds in some cases, presumably causing other effects).
 

Related to What is meant when it is said that a molecule is excited?

1. What does it mean for a molecule to be "excited"?

When a molecule is "excited," it means that the electrons within the molecule have absorbed energy and moved to a higher energy state. This can happen through various processes such as exposure to light or heat.

2. How does a molecule become excited?

A molecule can become excited through several mechanisms, including absorption of photons (light energy) or collisions with other molecules that transfer energy. The specific process depends on the type of molecule and the surrounding conditions.

3. What happens to a molecule when it is excited?

When a molecule is excited, its electrons move to higher energy levels. This can lead to changes in the molecule's physical or chemical properties, such as increased reactivity or a shift in its absorption spectrum.

4. How long does a molecule remain excited?

The duration of a molecule's excited state depends on the type of molecule and the surrounding environment. Some molecules may only remain excited for a fraction of a second, while others may stay in an excited state for hours or even days.

5. Can excited molecules return to their original state?

Yes, excited molecules can return to their original state by releasing the absorbed energy. This can happen through various processes such as emission of light or heat, or through collisions with other molecules. This return to the original state is known as "relaxation."

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