Knowledge Bank

Among the alkaline warth mononalide radicals Bal presents a particular challence to the spectroscopist because of the extremely congested optical spectra. Recently Johnson $etal.1$) succeeded in rotationally analyzing the $C2\Sigma -X2\Sigma 2(0,0)$ band system around 550 nm. For the correct identification of the observed hyperfine structure, however, an independent measurement of the X state hyperfine structure was required. Using the molecular beam laser-microwave double-resonance method we studied rotational transitions in the electronic ground state. At linewidths of about MHz the hyperfine structure from the weakly coupled iodine nucleus (1 = 5/2) was well resolved. Including the rotational constants of $X2\Sigma +$ from Forrine and $Doebl2$) in a fit procedure we determined his parameters (35 errors in parentheses): \begin{eqnarray*} BaI\ X^{2}\Sigma^{+} v=0&& b = 93.14(7) MHz\ && c = 52.2 (1) MHz\ && eqQ = -33.3 (5) MHz \end{eqnarray*}