# CO2 rotational constant

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1. Jan 20, 2015

### Nanosciencee

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?

2. Jan 20, 2015

### Quantum Defect

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?

3. Jan 20, 2015

### Nanosciencee

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

4. Jan 20, 2015

### Nanosciencee

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).

5. Jan 20, 2015

### Quantum Defect

"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.