Question 1

Paper 2Easy6 marks

Infrared radiation emitted by Earth’s surface reaches a carbon dioxide molecule in the atmosphere. Figure 1 shows two possible incoming infrared photons and two energy levels of the molecule. The molecule’s natural vibration frequency is f0f_0 In this model, a photon of frequency ff has energy E=hfE=hf

Candidate infrared photonsCO2 molecule: energy levelsA: f=f0B: f=f0/2energyE1E0ΔE=hf0
(a)

Using Figure 1, identify which photon can be absorbed by the molecule. Explain your choice using the resonance model and the energy levels.

[3]
(b)

As the molecule returns from E1E_1 to E0E_0 state the frequency of the infrared radiation emitted.

[1]
(c)

State the directions in which the radiation is emitted and explain how this can contribute to the greenhouse effect at Earth’s surface.

[2]

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