Question

In the middle of the rotation- vibration band of emission spectrum of HCl molecule, where the "zeroth" line is forbidden by the selection rules, the interval between neighbouring lines is Δω=0.79.1013 *-1. Calculate the distance between the nuclei of an HCl molecule.

Answer 1

In the rotation vibration band the main transition is due to change in vibrational quantum number v → v - 1. Together with this rotational quantum number may change. The “Zcroeth line” 0 → 0 is forbidden in this case so the neighbouring lines arise due to 1 → 0 or 0 → 1 in the rotational quantum number. Now