Knowledge Bank

The $A1\Sigma +\to X1\Sigma +$ band system of $BeH+,BeD+$ and $BeT+$ has been photographed at high resolution. The wavenumbers of 569 lines of $BeH+(\nu \prime \le 6,\nu \prime \prime \le 4)$, 664 lines of $BeD+(\nu \prime \le 6,\nu \prime \prime \le 4)$, and 571 lines of $BeT+(\nu \prime \le 7,\nu \prime \prime \le 5)$ have been measured with an estimated uncertainty of $0.05cm-1$. The data were combined with existing $data1$ for $BeH+$ (190 lines, $\nu \prime =2-6,\nu \prime \prime =6-10)$ in a simultaneous least-squares fit of the potential energy curves and radial Born-Oppenheimer breakdown functions associated with the hydrogen atom centre. The models employed for the two electronic states contained a total of only 30 adjustable parameters. The reduced standard deviation of the fit is $\sigma ^=1.00$, which indicates that the lines are reproduced by the fit, on average, to within the estimated experimental uncertainty.