Electronic energy transfer in Na2

The emission spectrum of the A 1Σ+u–X 1Σ+g band of Na2 has been recorded following both multimode and single mode excitation of the B 1Πu state using an argon ion laser. The spectral profile has been investigated as a function of excitation frequency, cell temperature and buffer gas pressure. Simulation of the band profile shows that the A 1Σ+u state is vibrationally inverted. This is interpreted through a populating mechanism involving collisional transfer from the B 1Πu to the (2) 1Σ+g state followed by radiative transfer to the A 1Σ+u state. The collision partner is most likely to be 2S state Na atoms. The emission is also found to be significantly negatively polarized with respect to the laser polarization plane. The results are discussed in the light of various theoretical models.