m v v0 T N2-N1 B21 α (v) = Ce^-β(v-v₀) (N₂ - N₁) hB₂₁ C=(m/2πkT)^½ β = mc²/2kTv₀²

c = 3x10⁸m/s h = 6.62 x 10^-34 J s k = 1.38 x 10^-23 J/ºK

I(v)/I₀(v)=e^α(v)x α x I/I₀

d Δv