Photons of energy 2.3 eV are incident on a low-pressure vapour. The energy levels of the atoms in the vapour are shown.

Photons of energy 2.3 eV are incident on a low-pressure vapour. The energy levels of the atoms in the vapour are shown.

$0 \mathrm{eV}-$

$-1.6 \mathrm{eV}-$

$-2.5 \mathrm{eV}-$

$-3.9 \mathrm{eV}-\quad \text{not to scale}$

What energy transition will occur when a photon is absorbed by the vapour?