ROTATIONAL STATE SELECTION AND ORIENTATION OF OH AND OD RADICALS BY ELECTRIC HEXAPOLE BEAM-FOCUSING

An electrostatic hexapole was used to state-select OH and OD radicals in single, low-lying, \J Omega M-J] rotational states. The radicals we re produced in a corona discharge, supersonic molecular beam source by dissociating H2O (D2O) seeded in Ar or He. Beam velocities ranged fro m 650 to 1850 m s(-1), and translational temperatures were less than 1 0 K for all expansion conditions. Measured beam flux densities, J, of selected states were high (e.g., J > 10(13) radicals cm(-2) s(-1) for the \3/2 +/-3/2 -/+3/2] states of OH seeded in He). Classical trajecto ry simulations reproduced the well-resolved rotational state structure of experimental beam-focusing spectra. Simulations were based on a St ark energy analysis of the rotational energy levels, including signifi cant effects due to A-doubling and spin-orbit coupling. Orientational probability distribution functions were calculated in the high-field l imit for all selectable states and demonstrate exceptional experimenta l control over collision geometry for scattering experiments.