# Rotational Quantum Number 0

1. Mar 7, 2014

### spaghetti3451

My book on Physics by Beiser specifies that the rotational energy levels of a diatomic molecule are given by J(J+1)/ℏ2, where J = 0, 1, 2, 3, ... .

However, in the next page, it goes on to mention that the lowest rotational energy level corresponds to J = 1.

I don't see why that shouldn't be J = 0.

Any comments would be greatly appreciated.

2. Mar 8, 2014

### spaghetti3451

Let me rephrase my question.

I know that the rotational quantum number starts at J = 0,

but do you count the lowest rotational energy state as J = 0 or as J = 1?

3. Mar 8, 2014

### Bill_K

J = 0 is the ground state. J = 1 is the first excited rotational state.