Chapter 11, Problem 11F.9BE

Interpretation Introduction

Interpretation:

The rotational constant for excited state and the change in bond length have to be stated.

Concept introduction:

During electronic transitions, there may be changes in both rotational and vibrational energy.  These lines due to vibrational fine structure consist of rotational fine branches and also consist of $\text{P,Q,}$ and $\text{R}$ branches.  For a $\text{P}$ branch, $\Delta J=-1$.  For a $\text{Q}$ branch, $\Delta J=0$ and for a $\text{R}$ branch, $\Delta J=+1$.  On increasing value of rotational quantum number, the spectral lines start to converge and appear at decreasing wavenumbers, that is, the $\text{P}$ branch has a band head.