Broad-band structured fluorescence from NaI

The emission spectrum of a molecular beam of NaI has been measured following excitation by the 248 nm KrF line of an excimer laser. The fluorescence structure, and the lifetime (17±2 ns), indicate the presence of a bound upper state not previously characterized. We identify this state as correlating with Na(3 2P)+I(5 2P3/2) atoms. Through numerical simulation using a Morse function representation for the upper state, we have determined approximate values for the well depth of 530±260 cm−1, well breadth of ∼1.8 Å−1, and equilibrium separation of ∼3.4 Å for this state. As a consequence of the breadth of this weakly bound excited state the bound→bound line spectrum spans a broad spectral range (87% of the ground state well depth) entirely comparable with spectra attributed to free→bound emission.