  The Raman spectrum of the superconductor MgB$_{2}$ has been measured as a
function of the Tc of the film. A striking correlation is observed between the
$T_{c}$ onset and the frequency of the $E_{2g}$ mode. Analysis of the data with
the McMillan formula provides clear experimental evidence for the collapse of
the electron phonon coupling at the temperature predicted for the convergence
of two superconducting gaps into one observable gap. This gives indirect
evidence of the convergence of the two gaps and direct evidence of a transition
to an isotropic state at 19 K. The value of the electron phonon coupling
constant is found to be 1.22 for films with T$_{c}$ 39K and 0.80 for films with
T$_{c}\leq$19K.
