[Ridak]

Hi friends need help with this.
Consider a diatomic molecule for which the rotational transition between the levels J=2 and J=3 occurs at a frequency of 112.0 GHz. Find the frequency of the transition between the levels with J-7 and J-8.

i am using E=n^2 h^2/8ml^2
we know frequency v= 112.0 GHz
Ea=(n3^2-n2^2)h^2/8ml^2
hVa=9-4*hbar/8ml^2
5hbar/8ml^2=Va
now h /8ml^2=Va/5
Eb=64-49h^2/8ml^2=hVb
Vb=15*h/8ml^2
Vb=15*112/5=336Ghz
is this correct?

[Corribus]

You appear to be using the energy formula for particle in a box.  You should be using the energy formula for the rigid rotor.