curve fit the function

I am trying to curve fit the following equation with parameters d, D, Ar, Tr each of them bounded in some range. The physical constants are: gamma = 26.76E7, n = 6.59E28, Ad = 2.099E-20

The equation is broken into several parts -

   w1=2*pi*x
    z1=(2*w1*d^2/D)^0.5
    w2=2*w1
    z2=(2*w2*d^2/D)^0.5
    J1=((1+5*z1/8+z1^2/8)/(1+z1+z1^2/2+z1^3/6+z1^5/81+z1^6/648))
    J2=((1+5*z2/8+z2^2/8)/(1+z2+z2^2/2+z2^3/6+z2^5/81+z2^6/648))
    R1_diff = Ad*(J1+4*J2)/(d*D)
    R1_rot = Ar*(Tr/(1+w1^2*Tr^2)+4*Tr/(1+(w2)^2*Tr^2))
    R1_IL = R1_diff + R1_rot

finally

return R1_IL

#Experimental x and y data points

xData = [2.00E+07,1.42E+07,1.01E+07,7.16E+06,5.09E+06,3.61E+06,2.57E+06,1.82E+06, ...
         1.29E+06,9.20E+05,6.53E+05,4.63E+05,3.29E+05,2.34E+05,1.66E+05,1.18E+05, ...
         8.39E+04,5.96E+04,4.24E+04,3.00E+04];

yData = [1.90E+01,2.11E+01,2.38E+01,2.66E+01,2.97E+01,3.26E+01,3.46E+01,3.70E+01, ...
         3.84E+01,4.00E+01,4.12E+01,4.22E+01,4.33E+01,4.39E+01,4.48E+01,4.54E+01, ...
         4.65E+01,4.64E+01,4.67E+01,4.67E+01];

and the bound parameters are

d = [2.00E-10, 3.5E-10], D = [3.0E-12, 4.00E-12], Ar = [3.00E9, 3.8E9], Tr = [5.00E-19, 6.9E-10]ll

I need to get the parameter values that will minimize the function and curve fit the plot of R1 vs x in loglog scale.

[dpb]

Reformatted Q? data/code so somebody can download easily -- dpb