The Na2 a 3Σ+u state. Rotationally resolved OODR 3Πg–a 3Σ+u fluorescence spectroscopy

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Abstract
Thirteen bound vibrational levels (v=0–12) and a portion of the continuum of the Na2 a 3Σ+ u state have been observed in rotationally resolved fluorescence spectra from single rotation‐vibration levels of two 3Π g states. These 3Π g states were populated by A 1Σ+ u ∼b 3Π u perturbation‐facilitated optical–optical double resonance from the X 1Σ+ g state. Analysis, using a LeRoy–Bernstein long‐range expression for the energy levels, produced an RKR potential curve from which were derived, in combination with recent results obtained by Barrow et al. on the X 1Σ+ g state, principal constants for the a 3Σ+ u state of r e =5.0911(30) Å, D e =174.45(36) cm−1, ω e =24.47(21) cm−1, and T e =5848.21(35) cm−1. In addition, the exchange interaction between two ground stateNa atoms was found from the difference between the X 1Σ+ g and a 3Σ+ u potential curves to be well represented by an exponential, A exp(‐BR), A=9.44(71)×105 cm−1, B=1.448(14) Å−1 for R≳5.0 Å.