Is there an error on Wikipedia's page on characteristic rotational temperature of HF?
The units of the inertial constant I are reported in $\pu{amu \cdot Å^2}$. One unified atomic mass unit (or Dalton) is approximately $\pu{1.660e-27 kg}$. Using the correct formula in MATLAB:
&gt;&gt; amu=1e-3/6.022e23;
&gt;&gt; h=6.626e-34; kb=1.3806e-23; tr=@(I) ((h/(2*pi))^2)/(2*I*kb*amu*1e-20);
&gt;&gt; tr(0.86)
ans =

 2.820249699307124e+01

Using instead $\pu{I= 0.80 amuÅ^2}$ from the NIST website returns a value closer to that on the Wikipedia table.