We present the first crossed beam scattering experiment using a Zeeman decelerated molecular beam. The narrow velocity spreads of Zeeman decelerated NO (X 2 Π 3/2 , j = 3/2) radicals result in high-resolution scattering images, thereby fully resolving quantum diffraction oscillations in the angular scattering distribution for inelastic NO-Ne collisions, and product-pair correlations in the radial scattering distribution for inelastic NO-O2 collisions. These measurements demonstrate similar resolution and sensitivity as in experiments using Stark decelerators, opening up possibilities for controlled and low-energy scattering experiments using chemically relevant species such as H and O atoms, O2 molecules or NH radicals.Establishing experimental tools to study molecular collisions with the highest possible level of detail has been an important goal in molecular physics for decades [1]. The sensitivity and resolution of the experiment depends on the control over the particles before the collision, and how they are detected afterwards. In recent years, the combination of Stark deceleration and velocity map imaging (VMI) to both control and probe the quantum state and velocity of molecules, has greatly enhanced the possibilities to investigate molecular collisions in crossed beam experiments [2]. The narrow velocity and angular spreads of Stark-decelerated beams result in scattering images with unprecedented radial and angular resolution, that can be exploited to resolve structure in the scattering images -and thus the differential cross section (DCS) of the scattering process -that would have been washed out using conventional molecular beams. Recent examples include the direct imaging of quantum diffraction oscillations [3][4][5], the measurement of correlated excitations in bimolecular collisions [6], and the probing of scattering resonances at low collision energies [7,8].Despite these successes and further prospects to unravel fine details of collision processes, the Stark deceleration technique has a major limitation. As the method relies on the interaction of neutral molecules with electric fields, it can only be applied to species with a sufficiently large electric dipole moment. Although these include important molecules for scattering studies [9, 10], many chemically relevant species like H, O and F atoms, O 2 molecules or ground state NH radicals exclusively have a magnetic dipole moment, rendering the Stark deceleration technique useless. Yet, these species are of paramount importance to molecular reaction dynamics [11], surface scattering [12], and the emerging fields of cold and ultracold molecules alike [13].Recently, various types of Zeeman decelerators -the magnetic analogue of a Stark decelerator -have been realized, and the successful deceleration [14-24] and subsequent trapping [25-30] of a variety of atomic and molecular species has been reported. Yet, the application of molecular decelerators in crossed beam experiments poses specific requirements on density, state purity, and velocity control o...

High-resolution measurements of angular scattering distributions provide a sensitive test for theoretical descriptions of collision processes. Crossed beam experiments employing a decelerator and velocity map imaging have proven successful to probe collision cross sections with extraordinary resolution. However, a prerequisite to exploit these possibilities is the availability of a near-threshold state-selective ionization scheme to detect the collision products, which for many species is either absent or inefficient. We present the first implementation of recoil-free vacuum ultraviolet (VUV) based detection in scattering experiments involving a decelerator and velocity map imaging. This allowed for high-resolution measurements of state-resolved angular scattering distributions for inelastic collisions between Zeeman-decelerated carbon C( 3 P 1 ) atoms and helium atoms. We fully resolved diffraction oscillations in the angular distributions, which showed excellent agreement with the distributions predicted by quantum scattering calculations. Our approach offers exciting prospects to investigate a large range of scattering processes with unprecedented precision.

We report on the Zeeman deceleration of ground-state NH radicals, using a decelerator that consists of 100 pulsed solenoids and 100 permanent hexapoles. Packets of state-selected NH (X 3 Σ − , N=0, J=1) radicals are produced with final velocities ranging between 510 m/s and 150 m/s. The velocity distributions of the packets of NH exiting the Zeeman decelerator are probed using velocity map imaging detection. We present a new 1+2' resonance-enhanced multiphoton ionization scheme for NH, that allows for velocity map imaging detection under ion recoil-free conditions. The packets of Zeeman-decelerated NH radicals, in combination with the new detection scheme, offer interesting prospects for the use of this important radical in high-resolution crossed-beam scattering experiments.

We present the design of a Velocity Map Imaging apparatus tailored to the demands of highresolution crossed molecular beam experiments employing Stark or Zeeman decelerators. The key requirements for these experiments consist of the combination of a high-relative velocity resolution for large ionisation volumes and a broad range of relatively low lab-frame velocities. The SIMION software package was employed to systematically optimise the electrode geometries and electrical configuration. The final design consists of a stack of 16 tubular electrodes, electrically connected with resistors, which is divided into three electric field regions. The resulting apparatus allows for an inherent velocity blurring of less than 1.1 m/s for NO + ions originating from a 3 × 3 × 3 mm ionisation volume, which is negligible in a typical crossed beam experiment. The design was recently employed in several state of the art crossed-beam experiments, allowing the observation of fine details in the velocity distributions of the scattered molecules.