= Photodissociation
{wiki}
<Photodissociation> separates a <molecule> into fragments after <photon absorption>. For an isolated parent with a single absorbed <photon>, <conservation of energy> gives
$$
h\nu+E_{\rm initial,int}=D_0+E_{\rm products,int}+E_{\rm recoil}.
$$
Internal excitation <energies> here are relative to the parent and product ground states used to define $D_0$; $E_{\rm recoil}$ is the total product translational <kinetic energy> in the parent's <centre of mass> frame. Measuring one product's <kinetic energy> is insufficient by itself. For two fragments of <masses> $m_A,m_B$, <conservation of momentum> gives $E_{\rm recoil}=E_A(m_A+m_B)/m_B$ when $A$ is detected. Unknown product excitation can conceal part of the available <energy>.
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