What is the ground-state energy and Bohr radius for each of the following two-particle systems?
(a) 2H, a bound state of a deuteron and an electron
(b) Positronium
(c) A bound state of a proton and a negative muon
(d) A gravitational bound state of two neutrons
What is the wavelength of the radiation emitted in the transition from the n=2 state to the n=1 state in each case? In what portion of the electromagnetic spectrum does this radiation reside?