Knowledge Bank

Using a single tunable dye laser, emission into the $a3\Pi$ and $ A^{\prime}^{1}\Pi$ states of BaO has been observed in an isotopically selective optical-optical double resonance (OODR) experiment involving a real intermediate level. Absorption in the 6240 {\AA} region of the $A^{1}\Sigma^{+} - X^{1}\Sigma^{+} $system [(0,1) band] is followed by absorption from the $A1\Sigma +(\nu =0)$ to a highly excited state (denoted $\nu \ast$) which has predominate $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma +$ character. Emission from $\nu \ast \to X1\Sigma +$ and $\nu \ast \to$, $A1\Sigma +$ was also observed as welt as both $A1\Sigma +\to X1\Sigma +$ single resonance and cascade fluorescence. The electronic transition moment for $\nu \ast \to a3\Pi$ emission is due to spin-orbit mixing of $a3\Pi$ and $A^\{\backslash prime\}^\{1\}\backslash Pi$, hence only $\Omega =1$ of $a3\Pi$ is observed. Intensities observed in $\nu \ast \to a3\Pi$ and $\backslash nu^\{*\}\; \backslash rightarrow\; A^\{\backslash prime\}^\{1\}\backslash Pi$ emission deviated from the expected 1:2:1 ratio for P, Q, and R branches, respectively. Four strong OODR lines were observed plus collision-induced satellites due to rotational relaxation in the $A1\Sigma +$ state. The tentative assignments $[(JA\leftarrow JX),(J\ast \leftarrow JA)$ for the strong sequential excitation lines are R(48), P(49); R(32), R(33) P(29), P(78); and P(18), R(17). Preliminary values for $B\nu \ast$ and the energy of $\nu \ast (J\ast =0)$ relative to $X1\Sigma +(\nu =0,J=0)$ have been calculated giving $B\nu \ast =0.240cm-1$ and $E\nu \ast =32 750 cm-1$.