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I have an assignment to derive the two following expressions:

R(J)-P(J)=2B'(2J+1)

R(J-1)-P(J+1)=2B''(2J+1)

where Bis the rotational constant and prime ' stands for upper level and bis '' for lower level.

B_{v}=B_{e}-α(v+1/2)

using the selection rules (I guess in this case ΔJ=±1) and ΔT=G(v')-G(v'')+F(J')-F(J'') where ΔT is the transition/energy difference

between two energy levels expressed in wavenumbers and F(J)=BJ(J+1)

G(v)=ω_{e}(v+1/2)-ω_{e}x_{e}(v+1/2)^{2}.

I don't understand how I'm going to put all of this together and I don't understand what they mean with R(J) and P(J) etc.

Thankful for any help!

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# Homework Help: Derive the relation between the P & R branches

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