Chapter 11, Problem 11.44E

(a) Using the expression for the energy of a $\text{2-D}$ rigid rotor, construct the expression for the energy difference between two adjacent levels, $E\left(m+1\right)-E\left(m\right)$. (b) For $\text{HCl}$, $E\left(1\right)-E\left(0\right)=20.7{\text{cm}}^{-1}$. Calculate $E\left(2\right)=E\left(1\right)$, assuming $\text{HCl}$ acts as a $\text{2-D}$ rigid rotor. (c) This energy difference is determined experimentally as $41.4{\text{cm}}^{-1}$. How good would you say a $\text{2-D}$ model is for this system?