A diatomic molecule in its ground electronic state absorbs one photon that excites it…
PHYSICS · Multi-part · A Level · Physics · Particles and radiation · Particles and radiation
Problem
A diatomic molecule in its ground electronic state absorbs one photon that excites it to state A. It then quickly absorbs a second photon and reaches the higher-energy state B. The energies of the states are:
Ground state: 0J (reference)
State A: 4.10×10−19J
State B: 8.25×10−19J
Immediately after reaching state B, the molecule relaxes directly back to the ground state, emitting a single photon.
Constants (if needed):
• c=3.00×108ms−1
• h=6.626×10−34Js
(a) Calculate the wavelength, in nanometres, of the photon absorbed in the first excitation (ground → A).
(b) Determine the wavelength of the photon absorbed in the second excitation (A → B).
(c) Calculate the wavelength of the photon emitted during the relaxation from state B to the ground state.
(d) For each of the three photons (two absorbed and one emitted), classify the radiation as ultraviolet, visible, or infrared, and justify each classification with appropriate numerical evidence.
(e) Propose a detection method (instrument or sensor type) suitable for monitoring the emitted photon in part (c), and explain how the photon’s spectral region influences the choice of detector.