Q1(m). Anthracene photodimerization

Answer in brief

Ideally one absorbed photon produces one dimer and consumes two anthracene molecules: Φ_(dimer)=1 or Φ_(disappearance)=2, depending on the stated convention.

Key points

• Absorption gives A*; a productive encounter with ground-state anthracene forms the dimer: A+hν→ A*, then A*+A→ A₂.
• Not every excited molecule reaches a productive encounter. Fluorescence, internal conversion, intersystem crossing and quenching compete with dimer formation, reducing the chemical yield.
• If 0.5 denotes anthracene disappearance per photon, the productive fraction is 0.5/2=0.25.