Bound-free Emission in the NaK Molecule

We are extending the analysis of the bound-free emission from the $4\,^3\Sigma^+$ electronic state to the $a(1)\,^3\Sigma^+$ repulsive state of the NaK molecule. In previous work, Burns {\it et al.} [J. Chem.~Phys. {\bfseries 119} 4743--4754 (2003)] measured spectra from initial vibrational levels up to $v = 8$, determined a refined potential for the $4\,^3\Sigma^+$ state, and obtained relative values of the transition dipole moment function $M(R)$ in the range $R \sim 3.8$~\AA\ to 4.6~\AA. Recent measurements include data for many additional vibrational levels up to $v = 34$ of the $4\,^3\Sigma^+$ state. The new data provide information about $M(R)$ for larger values of $R$, including a region where theoretical calculations have predicted sharp structure due to an avoided crossing. Using a version of R. J. Le~Roy's code BCONT that we modified, we will obtain values $M(R)$ for a larger range of $R$, and we will refine the inner repulsive wall of the potential for the $a(1)\,^3\Sigma^+$ state.