An atomic species emits light with a characteristic frequency f0 while at a rest state. A diatomic gas of such atomic species has been heated to temperature T′. Due to their random thermal motions, some atoms move toward or against an onlooker. Assuming that root mean square speed characterizes their thermal motions:
(i) Determine the expression for the fractional variation f0Δf between Doppler shifted frequencies corresponding to those moving straightly toward or against the onlooker, Assume mc2≫3kT′.
(ii) Compute Δf/f0 for a gas of oxygen atoms at 300 K.