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 the state-selective deceleration of atomic oxygen to final mean velocities in the range 500--125 m/s. We further characterize our decelerator with molecular oxygen, which, despite its heavier mass, is velocity tuned in the range 350--150 m/s. 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.
We use a multistage Zeeman decelerator to generate slow beams ($v\ensuremath{\simeq}100\phantom{\rule{0.16em}{0ex}}\mathrm{m}/\mathrm{s}$) of translationally cold, spin-polarized metastable $a\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{\ensuremath{\Sigma}}_{u}^{+}\phantom{\rule{4pt}{0ex}}{\mathrm{He}}_{2}$ molecules and perform a precision measurement of their spin-rotation fine structure. The spin polarization results from the elimination of the high-field-seeking
J=N spin-rotational component of each rotational level (rotational quantum number
N) by the Zeeman deceleration process. By repopulating the
J=N component from the $J=N\ifmmode\pm\else\textpm\fi{}1$ low-field-seeking components using radio-frequency radiation, we measured the spin-rotation fine structure of 13 rovibrational levels with
v=0, 1 and
N=1–21. The low beam velocity and the resulting long interaction times with the radio-frequency radiation were exploited to determine the transition frequencies with a precision of 300 Hz.
We report on the use of multistage Zeeman deceleration to generate beams of
He2 molecules in the metastable $a\phantom{\rule{0.16em}{0ex}}{}^{3}{\ensuremath{\Sigma}}_{u}^{+}$ state with velocities tunable down to 100 m/s. The metastable molecules are generated by striking a discharge in a supersonic expansion of pure helium gas from a pulsed valve held at cryogenic temperature. The velocity and internal-state distributions of the metastable
He2 molecules are measured for nozzle temperatures of 300, 77, and 10 K by high-resolution photoelectron and photoionization spectroscopy. The deceleration process does not exhibit any rotational state selectivity with rotational levels up to ${N}^{\ensuremath{'}\ensuremath{'}}=21$ being populated, but eliminates molecules in spin-rotational sublevels with ${J}^{\ensuremath{'}\ensuremath{'}}={N}^{\ensuremath{'}\ensuremath{'}}$ from the beam, where ${J}^{\ensuremath{'}\ensuremath{'}}$ and ${N}^{\ensuremath{'}\ensuremath{'}}$ are the total and the rotational angular momentum quantum number, respectively. The lack of rotational state selectivity is attributed to the fact that the Paschen-Back regime of the Zeeman effect in the rotational levels of
He2 is already reached at fields of only 0.1 T.
We have demonstrated that supersonic beams of oxygen molecules
(O2) in the ground rotational state were slowed to a near standstill by a linear Zeeman decelerator and successfully confined spatially in an anti-Helmholtz magnetic trap. The translational temperature of the decelerated
O2 molecules was about 800 mK. The demonstrated trapping capability of paramagnetic species opens up various possibilities for the investigation of cold collisions and reactions of various radicals in the sub-kelvin regime by spatially confining them in a magnetic trap.
"Having three and four electrons, respectively, He
2+ and He
2 represent systems for which highly accurate \textit{ab-initio} calculations might become feasible in the near future\footnote{W.-C. Tung, M. Pavanello, L. Adamowicz, \textit{J. Chem. Phys.} \textbf{136}, 104309 (2012).}. With the goal of performing accurate measurements of the rovibrational energy-level structure of He
2+ by Rydberg spectroscopy of He
2 and multichannel quantum-defect theory extrapolation techniques\footnote{D. Sprecher, J. Liu, T. Kr\""ahenmann, M. Sch\""afer, and F. Merkt, \textit{J. Chem. Phys.} \textbf{140}, 064304 (2014).}, we have produced samples of helium molecules in the
a3Σu+ state in supersonic beams with velocities tunable down to 100\,m/s by combining a cryogenic supersonic-beam source with a multistage Zeeman decelerator\footnote{M. Motsch, P. Jansen, J. A. Agner, H. Schmutz, and F. Merkt, \textit{arXiv:1401.7774}.}. The molecules are formed at an initial velocity of 500 m/s by striking a discharge in the pulsed expansion of helium gas from a reservoir kept at a cryogenic temperature of 10 K. Using rotationally-resolved PFI-ZEKE (pulsed-field-ionization zero-kinetic-energy) photoelectron spectroscopy, we have probed the rotational-state distribution of the molecules produced in the discharge and found vibrational levels up to
ν′′=2 and rotational levels up to
N′′=21 to be populated. The molecular beam is coupled to a multistage Zeeman decelerator\footnote{N. Vanhaecke, U. Meier, M. Andrist, B. H. Meier, and F. Merkt, \textit{Phys. Rev. A} \textbf{75}, 031402(R) (2007).} that employs pulsed inhomogeneous magnetic fields to further reduce the beam velocity. By measuring the quantum-state distribution of the decelerated sample using photoelectron and photoionization spectroscopy we observed no rotational or vibrational state-selectivity of the deceleration process, but found that one of the three spin-rotation components of the He
2 a3Σu+ rotational levels is eliminated."
A modular multistage Zeeman decelerator consisting of an array of solenoids has been developed to control the velocity of cold, paramagnetic atoms and molecules in supersonic beams. The translational motion these atoms and molecules was manipulated with high precision by exploiting the interaction between their magnetic moments and timedependent inhomogeneous magnetic elds. Deceleration was achieved by pulsing high currents (up to 300 A) through the solenoids of the decelerator with pulse sequences calculated to preserve the phase-space density of the atomic and molecular samples while removing a preset amount of kinetic energy. For the operation of the multistage Zeeman decelerator, solenoids and electronic units were developed to generate strong magneticeld pulses (> 2 T) with rise and fall times of only a few microseconds. An accurate three-dimensional particle-trajectory simulation program has been developed to analyze the deceleration process and optimize its e ciency. This software was thoroughly tested by systematic comparison with experimental results and enabled, in combination with measurements, the complete characterization of the spatial and velocity distributions of the decelerated and trapped atoms for di erent sets of experimental conditions. The program was essential to achieve a complete interpretation of the dynamics of the deceleration process and to devise a strategy to e ciently load the decelerated atoms and molecules into magnetic quadrupole traps. In a rst experiment, hydrogen atoms seeded in a supersonic expansion of Kr have been decelerated from an initial velocity of 435 m/s to nal velocities as low as 107 m/s in a 12-stage Zeeman decelerator. The operation of the decelerator has been analyzed by comparing the results of numerical particle-trajectory simulations with those of independent measurements of the velocity distribution by ion time-ofight mass spectrometry following photoionization of the decelerated atoms. The velocity distribution of the decelerated atom cloud was found to have a half width at half maximum of 25± 12 m/s corresponding to a temperature of ∼ 40 mK. The phase stability of the multistage-Zeeman-deceleration process has been investigated by numerical particle-trajectory simulations and experimental measurements on deuterium atoms in a 24-stage Zeeman decelerator. A one-dimensional analytical model of the phase stability in a multistage Zeeman decelerator was adapted from a one-dimensional model of phase stability in a multistage Stark decelerator and compared with the results of oneand three-dimensional particle-trajectory simulations. The comparison, which included the analysis of the e ects of nite switch-on and switch-o times of the deceleration pulses, revealed that transverse e ects in the decelerator lead to a considerable reduction of the