T=[233.40250 239.35995 243.59725 249.90110 254.20285 258.05660 262.54575 268.73452...
    272.85824 278.15304 283.27835 288.66575 292.99200 297.68075 ...
303.37210 309.73835 314.01480 319.24615 323.76605 327.75165 332.77260 339.09160];
tt=[23.40250 23.35995 23.59725 24.90110 25.20285 28.05660 22.54575 26.73452  22.8824 27.15304...
    23.27835 28.66575 29.99200 27.68075 33.37210 39.73835...
31.01480 31.24615 33.76605 37.75165 32.77260 33.09160];
V=[4.202 3.730 3.493 3.252 3.155 3.110 3.086 3.151 3.218 3.357 3.530 3.750 3.966 4.21 4.527 ...
        4.912 5.168 5.469 5.713 5.905 6.122 6.356];
a0=[0.5 0.5 1.0 4000 5000 0.02];
options=optimset('fminsearch');
a=fminsearch('expss',a0,options,T,tt,V)


%expss.m文件
function f=expss(a,T,tt,V)
Y1=12*(a(2)*tt+a(6)*exp(a(4)*(1./T-1./(293*tt))));
Y2=a(3)*exp(a(5)*(1./T-1/293))./(a(3)*tt+exp(a(5)*(1./T-1/293)));
Y3=a(6)*exp(a(4)*(1./T-1/293));
Y=Y1./(a(1)+Y2+a(2)+Y3);
f=sum((V-Y).^2);



Running Result:
Exiting: Maximum number of function evaluations has been exceeded
         - increase MaxFunEvals option.
         Current function value: 8.337835 


a =

  1.0e+004 *

    0.0001    0.0000    0.0000    0.0082    1.1541    0.0000