# CO2 rotational constant

Hey!

I have a problem. The problem is simple: calculate CO2 rotational constant. I have values for J (ground state and excited state), with those grades I have to calculate rotational constant. I know that for J=0,2,4.. it is just in ground state and for J=1,3,5..it is excited state. But how do I can calculate B(0) and B(1), because with those I can calculate B(e). I also know that I have to plot and from slope I get those B grades, but what are in x/y-axis?

Quantum Defect
Homework Helper
Gold Member
Hey!

I have a problem. The problem is simple: calculate CO2 rotational constant. I have values for J (ground state and excited state), with those grades I have to calculate rotational constant. I know that for J=0,2,4.. it is just in ground state and for J=1,3,5..it is excited state. But how do I can calculate B(0) and B(1), because with those I can calculate B(e). I also know that I have to plot and from slope I get those B grades, but what are in x/y-axis?

You are confused, a bit.

For a rigid rotor, the energy levels are given by: E_rot = B* J*(J+1), J = 0, 1, 2, ...
For a non-rigid rotor, there are additional terms (centrifugal distortion constant, etc.)

Usually, you are given the energy levels or the transition energies between levels, and you use this information to find the rotational constant.

What data do you actually have?

Just wavenumbers for different J grades in P and R branch, nothing else.

You are confused, a bit.

For a rigid rotor, the energy levels are given by: E_rot = B* J*(J+1), J = 0, 1, 2, ...
For a non-rigid rotor, there are additional terms (centrifugal distortion constant, etc.)

Usually, you are given the energy levels or the transition energies between levels, and you use this information to find the rotational constant.

What data do you actually have?

I dont need to calculate energy levels, just rotational constant B(e). I have to check statistical weight and be sure which J grades are valuable (odd or even). And from that information I have to plot two graph to get B(0) and B(1).

Quantum Defect
Homework Helper
Gold Member
Just wavenumbers for different J grades in P and R branch, nothing else.

"P and R branch" suggests that you are calculating a ro-vibrational (Infrared or Raman) spectrum. You really have not provided enough information to allow me to give any help with what you are trying to do. Look at other posts in the "Homework" section of "Physics Forums" to see how people present these problems.