absorbance and fluorescence

Question

In which of the following cases does absorbance and fluorescence occur:

a) a molecule returns to the ground state electron from a triplet excited state losing its extra energy with the photon radiation

b) a molecule returns to the ground state electron from a single excited state losing its extra energy with the photon radiation

c) a molecule passes to a lower oscillating level losing its additional energy

d) absorbs energy

e) absorbs adequate energy by switching from the ground state S₀ to an excited state

explain the answer

Answer 1

Fluorescence is when an atom absorbs a photon and quickly emits a photon of a longer wavelength. Key to this is that it must happen almost immediately. Changing a spin state is very rare and so if this is involved, the result is not a quick process but rather the much longer-lasting phosphorescence.

Absorbance is when an atom absorbs a photon and gains energy.

So, with this in mind,

a) is neither, since it neither absorbs a photon nor relaxes into the same spin state

b) is fluorescence

c) is neither, as it does not emit a photon nor absorb a photon

d) is a little unclear, but since it does not make explicit mention of absorbing a lot of energy, this is probably neither since it doesn't absorb from a photon.

e) is absorption, as molecules usually only go to excited states through absorption of a photon.