NaH: Studies of the X 1Σ+ state near dissociation and of the radiative lifetimes and collision cross sections of the A 1Σ+ state

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Abstract
With a dye laser pumped by an excimer laser, the NaH A 1Σ+ state has been excited up to v′=21. Its decay to the X 1Σ+ ground state has been observed up to v″=19, a vibrational level close to the dissociation limit, allowing us to obtain a precise value of the X 1Σ+ dissociation energy: De=15 785±20 cm−1. For v″≳15, the vibrational spacings and the rotational constants decrease very rapidly, as also observed recently in CsH, due to a sudden change of configuration mixing. The A 1Σ+ radiative lifetimes do not vary appreciably from v′=3 to v′=18, τ=27±2 ns, but increase to 35±2 ns at v′=21. The quenching and rotational transfer collision cross sections of the A 1Σ+ state with H2 have nearly the same values for a given v′. They increase from v′=4 to v′=21 as do the calculated electric dipole moments and the geometric extent of the levels.