The Na2 <i>a</i> 3Σ+<i>u</i> state. Rotationally resolved OODR 3Π<i>g</i>–<i>a</i> 3Σ+<i>u</i> fluorescence spectroscopy

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 3Πg states. These 3Πg states were populated by A 1Σ+u∼b 3Πu 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 re=5.0911(30) Å, De=174.45(36) cm−1, ωe=24.47(21) cm−1, and Te=5848.21(35) cm−1. In addition, the exchange interaction between two ground state Na 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.