In rotational (microwave) spectroscopy, the Kth energy level is BK(K + 1), B = constant. It turns out the each Kth level is (2K + 1) degenerate. Now, as the energy level increases, does this mean that a single molecule will be in all these states at once, or in one of them? Or does it mean that the number of MOLECULES undergoing a transition to a higher energy state increases? I am confused about the interpretation of this. I know that the spectrum gives a nice curve shape, increasing first, because of ^^^^ and then decreasing because of the Boltzmann Population Law ( the no. of molecules undergoing transitions to higher states decreases as the energy between the states increases). I hope someone can clarify what is actually going on here. Thanks!!!