One-dimensional confinement of magnetically decelerated supersonic beams of ${\text{O}}_2$ molecules

We have demonstrated that supersonic beams of oxygen molecules $\left({\text{O}}_2\right)$ 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 ${\text{O}}_2$ 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.

Figure 1

(a) Schematic of the Zeeman decelerator. The system consists of a cold pulsed nozzle (NZ), a skimmer (SK), a ${\text{liquid-N}}_2$ cooled 80-stage Zeeman decelerator (ZD), an anti-Helmholtz magnetic trap (TR), and a microchannel plate (MCP) detector. (b) Cross section at the end of the Zeeman decelerator and trap. (c) Cross section of the simulated magnetic flux density $B$ of the trap at 600 A. Legends for the coil cross section are shown at the bottom of the panel. (d) Zeeman shift of ${\text{O}}_2$ in the $N^{\prime \prime }=1$ ground rotational state. Dashed black line: $J^{\prime \prime }=0$; solid red (medium grey) lines: $J^{\prime \prime }=2$; and solid blue (dark grey) lines: $J^{\prime \prime }=1$. The LFS states we focused on in this study are shown by bold lines.

Figure 2

(a) TOF of free flight of ${\text{O}}_2$ beam seeded in Kr (dashed black trace), and decelerated beams (colored or gray-scaled traces) detected by REMPI. The mean final longitudinal velocity of each decelerated ${\text{O}}_2$ packet is shown. The initial velocity of the target ${\text{O}}_2$ molecule was 320 ${\mathrm{ms}}^{-1}$ (black arrow). (b) Black trace: A REMPI frequency spectrum of a supersonic beam of ${\text{O}}_2$ seeded in Kr. The spectrum was taken with the previous 15-stage Zeeman system [18]. Sticks at the bottom: simulated intensities for transitions from the $J^{\prime \prime }=2$ [red (medium grey) sticks], $J^{\prime \prime }=1$ [blue (dark grey) sticks], and $J^{\prime \prime }=0$ [green (light grey)] states at a rotational temperature of 5 K [13]. Top red (medium grey) trace: The $F_3$ component of the REMPI frequency spectrum of decelerated ${\text{O}}_2$ at $v=231\text{m}{\text{s}}^{-1}$. (c) The peak height of the observed REMPI peaks at different final decelerated velocities. Blue (dark grey): experiment. Red (medium grey): simulation. The peak height is normalized to that at 231 ${\mathrm{ms}}^{-1}$.

Figure 3

(a) Current profiles of the front [blue (dark grey) trace] and rear [red (medium grey) trace] coils of the trap. (b) Observed TOF with the trap fields on [red (medium grey)] and off (black). Raw data (dotted lines) and slightly smoothed traces (solid lines). The black trace for the trap fields off is shifted downward slightly to avoid overlapping of the two traces. (c) Simulated TOF with the trap fields on [solid red (medium grey) curve] and off (solid black curve). The dotted curves represent contributions from the $|2,2\rangle$ [red (medium grey)], $|1,0\rangle$ [green (light grey)], and $|1,1\rangle$ [blue (dark grey)] states to the trap-on TOF signal. (d) Simulated TOF with the trap fields on for $>600\mu \text{s}$ for the $|2,2\rangle$ [bold red (medium grey)], $|1,0\rangle$ [green (light grey)], and $|1,1\rangle$ [blue (dark grey)] states.