A quantum system (a molecule) has the energy levels shown in Figure P29.59. A large number of these molecules in their ground states make up a gas. 

(a) Suppose we want to excite these molecules to the state labeled E₂ by shining light on the gas. What wavelength of light should we use? 

(b) If we expose the molecules to a continuous spectrum of light, photons of particular wavelengths might be absorbed. What wavelength photons would you expect to be absorbed? Do not assume the molecules all start in their ground state. Explain why that assumption makes sense.