Knowledge Bank

High-resolution ($\sim 0.02$ $cm-1$) spectra of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH4$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CH4$ were recorded in the $6000cm-1$ region, and isotope shifts were measured for several clearly resolved vibration-rotation $lines1$ The $2\nu 3$ spectrum of $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}CH4$ has now been analyzed for the first time. Nineteen spectroscopic constants have been determined for this band using an algorithm for fitting spherical-top vibration-rotation lines In the P-, Q-, and R-branches simultaneously. The $2\nu 3$ $spectrum2$ of $\mathrm{<mrow\; data-mjx-texclass="ORD">12</mrow>}CH4$ has been re-analyzed using this formalism; however, only sixteen spectroscopic constants could be determined with statistical significance because of the smaller fine-structure splittings inherent in this molecular band.