Absorption cross section
= Absorption cross section
{title2=$\sigma_{\rm abs}(\lambda)$}
The effective area per target for absorbing incident radiation at a specified <wavelength>. For independent absorbers with number column $N$, the absorption <optical depth> is $\tau=\sigma_{\rm abs}N$. Absorption does not guarantee a particular chemical product; a channel's <quantum yield> is also needed in its <photolysis rate coefficient>.