Collisional depolarization of state selected (J,MJ) BaOA 1Σ+ measured by optical–optical double resonance

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Abstract
The optical–optical double resonance (OODR) technique is used to investigate the change in magnetic quantum number (M) a state selected molecule undergoes on collision with other molecules. A first linearly polarized dye laser prepares A 1Σ+BaO(v = 1) in the J = 1, M = 0 sublevel. The extent of collisional transfer to other M sublevels of both J = 1 and J = 2 is then probed by a second polarized dye laser which induces fluorescence from the C 1Σ+ state. Elastic collisions (ΔJ = 0) between BaO (A 1Σ+) and CO2 are observed to change M from 0 to ±1 leaving J unchanged. The total elastic M‐changing cross section is σΔMCO2 = 8.4±2.4 Å2. Inelastic collisions (ΔJ = +1’ which transfer molecules to j = 2 also cause M changes. with both Ar and CO2 as collision partners. M, the space‐fixed projection of J, is found to be neither conserved nor randomized. Quantum atom–diatom collision models with quantization axis along the relative velocity vector are considered. Transition amplitudes in this system are evaluated using the l‐dominant and CS approximations.