Measurement of product alignment in beam–gas chemiluminescent reactions

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Abstract
A procedure is developed for determining the product rotational alignment in the center of mass frame from polarization measurements of the chemiluminescent atom–diatom exchange reaction A+BC→AB+C under beam–gas conditions. The degree of product alignment with respect to the initial relative velocity reaches a maximum when all reagent orbital angular momentum appears as product rotational angular momentum. For beam–gas chemiluminescence, this implies a limiting degree of polarization of the product emission referenced to the beam axis about which the initial relative velocities are cylindrically symmetric. Calculations are carried out to determine this limiting chemiluminescent polarization for a wide range of beam-gas reaction conditions. Averages over initial conditions are performed by Monte Carlo sampling. These calculations show that under realistic conditions the degree of beam–beam polarization does not exceed twice that of beam–gas polarization. Product polarization is measured in the beam–gas chemiluminescent reaction Ca(1D)+HCl→CaCl(B 2Σ+)+H and found to be greater than 20%. Because of kinematic constraints, this value closely approaches the calculated limiting polarization.