Page "Geiger–Müller tube" Paragraph 23

If a poor diatomic gas quencher were introduced to the tube, the positive argon ions, during their motion toward the cathode, would have multiple collisions with the quencher gas molecules and transfer their charge and some energy to them.

Neutral argon atoms would then be produced and the quencher gas ions would reach the cathode instead, gain electrons in excited states which would decay by photon emission, thereby producing spurious tube discharge as before.

However, effective quencher molecules, when excited, do not lose their energy by photon emission but by dissociation into neutral quencher atoms.

No spurious output pulses are then produced.