# I Terminology - the upper state

#### Paperfish

Terminology - the "upper state"

Hi there!

I'm reading a paper at the moment that describes a formula for an absorption coefficient with regard to radiative transfer. One of the variables in it is referred to as "N2". It describes N2 as "The number density of atoms in the upper state".

With oxygen as an example, would N2 simply refer to the number of atoms in the outer shell? ie: 6?

My apologies if this is a bit obvious. I'm afraid I'm new to all this, and this terminology doesn't immediately appear to be standard.

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#### DrClaude

Mentor
With oxygen as an example, would N2 simply refer to the number of atoms in the outer shell? ie: 6?
How many atoms are there in an atom???

formula for an absorption coefficient with regard to radiative transfer
So it is considering the transition between two states. The "upper state" then refers to the higher-energy state, and N2 is related to how many atoms are to found in that excited state at a given time.

#### Paperfish

My post finally gets a reply after 7 years, and it's revealed to not make sense. Amazing! Apologies, for that typo, it was meant to read:

"With oxygen as an example, would N2 simply refer to the number of electrons in the outer shell? ie: 6?"

And just to check, when you say "...and N2 is related to how many atoms are to found in that excited state at a given time", you do mean atoms and not electrons?

#### DrClaude

Mentor
My post finally gets a reply after 7 years,
We're doing some spring cleaning:

and it's revealed to not make sense. Amazing! Apologies, for that typo, it was meant to read:

"With oxygen as an example, would N2 simply refer to the number of electrons in the outer shell? ie: 6?"
No, this has nothing to do with electron shells.

And just to check, when you say "...and N2 is related to how many atoms are to found in that excited state at a given time", you do mean atoms and not electrons?
Yes, atoms. Not all the context was given, by I inferred that this deals with transitions between two states in an atom. The "number density of atoms in the upper state" refers to how many atoms are found in that upper (excited) state (it is not a single atom that is considered,but an ensemble of atoms, some will be in the lower state, some in the upper state).

#### Paperfish

Thank you so much for revisiting this and clarifying.

"Terminology - the upper state"

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