Knowledge Bank

Extensive collections of literature data involving the $A1\Sigma +$ and $X1\Sigma +$ states of $LiH$ and the $A1\Sigma u+$ and $X1\Sigma g+$ states of $Li2$ have been employed in direct least-squares fits of the radially dependent Hamiltonians. Vibration-rotational and pure rotational transition energies for the ground $X1\Sigma +$ state of $\mathrm{<mrow\; data-mjx-texclass="ORD">6</mrow>}LiH$, $\mathrm{<mrow\; data-mjx-texclass="ORD">7</mrow>}LiH$, $\mathrm{<mrow\; data-mjx-texclass="ORD">6</mrow>}LiD$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">7</mrow>}LiD$, along with the entire collection of $A1\Sigma +-X1\Sigma +$ emission and absorption data for the four isotopomers, are used in the fit for LiH; the data set for $Li2$ consists of more than 6000 $A1\Sigma u+-X1\Sigma g+$ absorption lines. The Born-Oppenheimer potentials are represented by a modified Lennard-Jones function that provides for correct behaviour in the near dissociation, long-range region of the potential. The LiH data set extends over $\approx 65$ and 80% of the well depths of the $A1\Sigma +$ and $X1\Sigma +$ states, respectively, while the $Li2$ data covers $\approx 70$ and 99.97% of the well depths (extending out to more than 14 \AA in the ground $X1\Sigma g+$ state). The fits take full account of Born- Oppenheimer breakdown effects, and reproduce the measured line positions to within their estimated accuracies.