= Ortho-para conversion heat
{title2=$Q=x_oM\hbar^2/(m_p^2r^2)$}
For <hydrogen> approximated as a <linear rigid rotor>, the $\ell=1$ to $\ell=0$ <energy> decrease is $\hbar^2/I$, with <moment of inertia> $I\simeq m_pr^2/2$. A sample of mass $M$ initially containing an <orthohydrogen> fraction $x_o$ therefore releases $Q\simeq x_oM\hbar^2/(m_p^2r^2)$ on complete conversion to the lowest <parahydrogen> level. This estimate neglects the <electron> contribution to molecular mass and changes of the rotational constant with environment. It describes an internal <heat> load that external insulation cannot remove.
Back to article page
