# Rotational spectrum assignment

#### jl29488

If I have the energy value (in cm-1) of a specific line in the rotational spectrum, how do I find out/assign the correct J''-J' values?

I know the selection rules for J to be +/- 1 for each rotational transition but I'm not sure how you can correctly identify which J value it is if your only given the energy.. The rotational parameter B isn't specified either so I'm puzzled.

Any help?

#### Borek

Mentor
I don't think it is possible to assign anything to just a single line.

#### Quantum Defect

Homework Helper
Gold Member
If I have the energy value (in cm-1) of a specific line in the rotational spectrum, how do I find out/assign the correct J''-J' values?

I know the selection rules for J to be +/- 1 for each rotational transition but I'm not sure how you can correctly identify which J value it is if your only given the energy.. The rotational parameter B isn't specified either so I'm puzzled.

Any help?
Do you know what the molecule is?