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...

We present a concept for a multistage Zeeman decelerator that is optimized particularly for applications in molecular beam scattering experiments. The decelerator consists of a series of alternating hexapoles and solenoids, that effectively decouple the transverse focusing and longitudinal deceleration properties of the decelerator. It can be operated in a deceleration and acceleration mode, as well as in a hybrid mode that makes it possible to guide a particle beam through the decelerator at constant speed. The deceleration features phase stability, with a relatively large six-dimensional phase-space acceptance. The separated focusing and deceleration elements result in an unequal partitioning of this acceptance between the longitudinal and transverse directions. This is ideal in scattering experiments, which typically benefit from a large longitudinal acceptance combined with narrow transverse distributions. We demonstrate the successful experimental implementation of this concept using a Zeeman decelerator consisting of an array of 25 hexapoles and 24 solenoids. The performance of the decelerator in acceleration, deceleration, and guiding modes is characterized using beams of metastable helium ( 3 S) atoms. Up to 60% of the kinetic energy was removed for He atoms that have an initial velocity of 520 m/s. The hexapoles consist of permanent magnets, whereas the solenoids are produced from a single hollow copper capillary through which cooling liquid is passed. The solenoid design allows for excellent thermal properties and enables the use of readily available and cheap electronics components to pulse high currents through the solenoids. The Zeeman decelerator demonstrated here is mechanically easy to build, can be operated with cost-effective electronics, and can run at repetition rates up to 10 Hz.

Zeeman deceleration is a relatively new technique used to obtain full control over the velocity of paramagnetic atoms or molecules in a molecular beam. We present a detailed description of a multistage Zeeman decelerator that has recently become operational in our laboratory [Cremers et al., Phys. Rev. A 98, 033406 (2018)], and that is specifically optimized for crossed molecular beams scattering experiments. The decelerator consists of an alternating array of 100 solenoids and 100 permanent hexapoles to guide or decelerate beams of paramagnetic atoms or molecules. The Zeeman decelerator features a modular design that is mechanically easy to extend to arbitrary length, and allows for solenoid and hexapole elements that are convenient to replace. The solenoids and associated electronics are efficiently water cooled and allow the Zeeman decelerator to operate at repetition rates exceeding 10 Hz. We characterize the performance of the decelerator using various beams of metastable rare gas atoms. Imaging of the atoms that exit the Zeeman decelerator reveals the transverse focusing properties of the hexapole array in the Zeeman decelerator.

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.

Multistage Zeeman deceleration is a technique used to reduce the velocity of neutral molecules with a magnetic dipole moment. Here we present a Zeeman decelerator that consists of 100 solenoids and 100 magnetic hexapoles, that is based on a short prototype design presented recently [Phys. Rev. A 95, 043415 (2017)]. The decelerator features a modular design with excellent thermal and vacuum properties, and is robustly operated at a 10 Hz repetition rate. We use this decelerator to demonstrate for the first time the state-selective deceleration of atomic oxygen to final mean velocities in the 500 -125 m/s range. We characterize our decelerator further with molecular oxygen, which despite its heavier mass is velocity tuned in the 350 -150 m/s range. This corresponds to a maximum kinetic energy reduction of 95% and 80% for atomic and molecular oxygen, respectively. The long multistage Zeeman decelerator presented here demonstrates that the concept of using alternating hexapoles and solenoids is truly phase stable. This Zeeman decelerator is ideally suited for applications in crossed beam scattering experiments; the state-selected and velocity controlled samples of O atoms and O2 molecules are particularly relevant for studies of inelastic and reactive processes.