Four-vector study of the spin-changing collision Ba[(6s)1(6p)1, 1P1→(6s)1(6p)1, 3P2]/H2

Abstract

The spin-changing (6s)¹(6p)¹, ¹P₁→(6s)¹(6p)¹, ³P₂ transition of barium induced by single collisions with H₂ has been studied using a crossed beam apparatus. An m_j-selective preparation and detection of barium was achieved using the pump and probe technique in the presence of a magnetic field that breaks the degeneracy of the barium magnetic sublevels. The probe laser was scanned across the (6s)¹(6p)¹, ³P_2,mj′→(6s)¹(7s)¹, ³S_{1, mj″} multiplicity. Analysis of the Doppler profiles of each line reveals the angular distribution of scattered barium atoms, the polarization of which is selected both before and after the collision. This is therefore a four-vector correlation experiment, and it is the first to document spin-changing transitions of alkaline-earth-metal atoms induced by a molecular target. It must be emphasized that all four vectors in the present experiment do not refer to the same quantization axis, whereas in the standard notion of n-vector correlation experiments, the n-vectors refer to the same axis. The results of the present work are discussed in the light shed by other results obtained on the same experiments with only two and three vectors controlled. A collision mechanism is proposed that accounts for all the existing experimental results on this process.