Direct observation of product-pair correlations in rotationally inelastic collisions of ND3 with D-2

We present a combined experimental and theoretical study of state-to-state inelastic scattering of ND3(j = 11-) with D2 (j = 0, 1, 2, 3) molecules at collision energies around 800 cm-1. Using a crossed molecular beam apparatus which employs the combination of Stark deceleration and velocity map imaging, we observe the correlated rotational excitations of both collision partners. For D2, both elastic (ΔjD2 = 0), inelastic excitation (j = 0 →j = 2) and inelastic de-excitation (j = 2 →j = 0) processes are observed. For a number of final ND3 states, inelastic channels in which D2 is rotationally excited or de-excited appear surprisingly strong. The experimental results are in excellent agreement with the predictions from quantum scattering calculations which are based on an ab initio ND3-D2 potential energy surface.status: publishe

Cold Collisions in a Molecular Synchrotron

We study collisions between neutral, deuterated ammonia molecules (ND_{3}) stored in a 50 cm diameter synchrotron and argon atoms in copropagating supersonic beams. The advantages of using a synchrotron in collision studies are twofold: (i) By storing ammonia molecules many round-trips, the sensitivity to collisions is greatly enhanced; (ii) the collision partners move in the same direction as the stored molecules, resulting in low collision energies. We tune the collision energy in three different ways: by varying the velocity of the stored ammonia packets, by varying the temperature of the pulsed valve that releases the argon atoms, and by varying the timing between the supersonic argon beam and the stored ammonia packets. These give consistent results. We determine the relative, total, integrated cross section for ND_{3}+Ar collisions in the energy range of 40-140  cm^{-1}, with a resolution of 5-10  cm^{-1} and an uncertainty of 7%-15%. Our measurements are in good agreement with theoretical scattering calculations.status: publishe