(*probability of passing the barrier of height V0*)
V0=2.
a=3.
kappa=Piecewise[{{Sqrt[2(Energy-V0)],Energy>V0},{Sqrt[2(V0-Energy)],Energy<V0}}]

Plot[{Piecewise[{{(1+(1/(4(Energy/V0-1)Energy/V0))(Sin[kappa*a])^2)^(-1),Energy>V0},{(1-(1/(4(Energy/V0-1)Energy/V0))(Sinh[kappa*a])^2)^(-1),Energy<V0}}],1,100*(Energy-V0)},{Energy,0,8},PlotStyle->Thickness[0.004],Filling->Bottom,PlotRange->{0.,1.01}]

kappa