Evaluation of band gap from transmittance

Question

How can I evaluate the band gap of my ZnO thin film.

Thickness=d=80 nm I’m aware of alpha=-1/d*log(T) But I can’t fit a line to my data. And: How can I smoothen my data on about 346 nm? Do you have any other idea for calculation of band gap from Transmittance and Absorbtion of light by thin films?

h=4.13566733e-15;            %# eV.s 
c=299792458;                 %# m/s 
                             %# landa in (nm) 
nu=c./(landa*1e-9);          %# 1/s 
alpha=-1/(50e-7)*log(T50);   %# 1/cm 
E=h*nu;                      %# eV 
Y=alpha.^2; 
plot(E,Y);

Data: 80.txt