Theoretical study of highly excited 1Σ+ and 1Πstates of NaLi and experimental observation of the interacting 51Σ+ and 61Σ+ states

Theoretical multireference configuration interaction (MRDCI) calculations on the excited 1Σ+ and 1Π states of NaLi are presented. They improve the results of a previous study by two of the present authors, resolve some differences with other theoretical results and lead to overall good agreement with experimental observations. To extend the experimental data base of electronic states in NaLi, a previously unknown 1Σ+ state is investigated by polarisation labelling spectroscopy. Comparison with accompanying and previous theoretical calculations leads to a conclusion that the observed system consists of two band systems switching smoothly from one adiabatic state to the other and allows assignment of the bands as 51Σ+ ← X1Σ+ in the lower energy part and to 61Σ+ ← X1Σ+ for higher energies.