Knowledge Bank

Detailed measurements have been made of the absorption cross section of $Cs2$ in the visible $(C\leftarrow X1\Sigma g+$ and $D\leftarrow -X1\Sigma g+$ systems) and of $K2$ in the red $(B1\Pi u\leftarrow X1\Sigma g+$). The $Cs2$ values, extending from 4700 to 6700 {\AA}, vary from about 0.01 to 1.2 {\AA}$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$. A representative value in the more prominent blue and red regions of the smeared-out spectrum is several tenths {\AA}$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$. The $K2$ cross section varies from 5 to 25 {\AA}$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ for averaged data from 6200 to 6750 {\AA}, with the peak of the clearly-visible band structure reaching 35 {\AA}$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$ at the (2,0) band head. The cross sections were measured from absorption spectra taken as a function of optical depth for varying amounts of several inert broadening gases. Maximum effective cell-length and temperature uncertainties lead to maximum estimated errors of roughly +25 to -35%.