Knowledge Bank

\hspace{3em}Doppler limited vib-rotational spectrum of the $A3\Pi 1u\leftarrow X1\Sigma g+$ system of $\mathrm{<mrow\; data-mjx-texclass="ORD">79</mrow>}$Br$2$, $\mathrm{<mrow\; data-mjx-texclass="ORD">81</mrow>}$Br$2$, and $\mathrm{<mrow\; data-mjx-texclass="ORD">79</mrow>}$Br$\mathrm{<mrow\; data-mjx-texclass="ORD">81</mrow>}$Br have been measured using a titanium sapphire laser. We adapted the two-tone modulation method to detect the absorption spectrum$1$. Measurements were made at room temperature in the region of 13000 -- 13700 \wn and at 150C in the region 12000 -- 13000 cm$\mathrm{<mrow\; data-mjx-texclass="ORD">-1</mrow>}$, as determined using a wavelength meter (Burleigh WA-1500) calibrated to the two-photon spectrum of Rb at 778 nm. The wavenumber accuracy measurement was estimated to be 0.005 \wn. About 10,000 lines of $P$, $Q$, and $R$-branches from $20\le J\le 100$ were assigned and spectroscopic constants of $\mathrm{<mrow\; data-mjx-texclass="ORD">79</mrow>}$Br$\mathrm{<mrow\; data-mjx-texclass="ORD">81</mrow>}$Br for $v' = 4 - 9 $ were determined using a global least-squares fit to all lines of the three isotopic species by taking the reduced mass ratios into consideration. The details of the results will be presented. \underline{\makebox[8cm]{}} 1. D.E.Cooper and R.E.Warren, {\sl J.Opt.Soc.Am.B, } {\bf 4,} 470 (1987).\