First observation of bound–continuum transitions in the laser-induced A 1Σ+u–X 1Σ+g fluorescence of Na2

Abstract

We report an interesting spectrum of Na₂ excited by a Kr⁺ (5682 Å) laser which shows a long series of R–P doublets in the region 5600–8000 Å and a continuum with three very broad maxima beyond 8000 Å. Our spectral analysis reveals that the laser populates the v′=34, J′=50 level in the A¹Σ⁺_u state from where Na₂ molecules fluoresce not only to the bound vibrational levels of the entire ground state potential well (3≤v″≤56) but also to the continuum levels above the well. We have made an independent theoretical quantitative prediction of the continuous emission and the agreement between experiment and theory is found to be excellent. Almost the entire (99.6%) ground state RKR potential is constructed using the bound state experimental data which leads to a more accurate value of the dissociation energy (D^″_e=6024±6 cm⁻¹). The feasibility of a continuously tunable near infrared Na₂ laser based upon this radiative dissociation process is discussed. Finally, we present a comprehensive bibliography for the Na₂ molecule similar to that given by Hessel and Vidal for Li₂ [J. Chem. Phys. 70, 4439 (1979)].