Intense and controlled beam of S($^1D_2$) atoms

TL;DR

This work addresses the need for intense, well-defined collision-energy sulfur beams by employing a 3 m multistage Zeeman decelerator to produce S($^1D_2$) atoms following CS$_2$ photolysis at 199.65 nm. The decelerator simultaneously manipulates S($^1D_2$) and ground-state S($^3P_J$), and, in deceleration mode, enables temporal separation to enhance quantum-state purity of the detected packet. A proof-of-principle elastic collision between S($^1D_2$) and Ar demonstrates sufficient beam density for high-resolution scattering studies and validates the approach for future reactive and quenching experiments at tunable energies. The setup lays a foundation for exploring S($^1D_2$) chemistry with potential extensions to S($^1D_2$)+H$_2$ and isotopologues, using heavier seed gases to access lower velocities and higher state purity as needed.

Abstract

We report the production of an intense and controlled beam of electronically excited sulfur atoms in the $^1D_2$ state using a multistage Zeeman decelerator. Sulfur atoms, generated via photolysis of CS$_2$, are produced in both the ground $^3P_J$ and excited $^1D_2$ states. We demonstrate that both can be manipulated using the decelerator, and that temporal separation between them can be achieved by operating in deceleration mode. This enables the generation of sulfur atom beams with a well-defined velocity, narrow velocity spreads, and an enhanced quantum-state purity. To assess the suitability of the beam for scattering studies, we performed a proof-of-principle elastic collision experiment with S($^1D_2$) and argon atoms. The observed velocity-map-imaging signal confirms that the S($^1D_2$) beam density is sufficient for detailed scattering studies. These results form the foundation for future studies of reactive and quenching processes involving S($^1D_2$) atoms at tunable and well-defined collision energies.

Figures (6)

• Figure 1: Schematic representation of the experimental setup. CS$_2$ seeded in neon exits a Nijmegen pulsed valve and is photolysed by a 199.65 nm laser. The resulting S atoms pass a skimmer and travel through a multistage Zeeman decelerator that consists of 127 pulsed solenoids and 127 permanent hexapoles. Afterwards, the S atoms are guided into the detection region by 7 additional hexapoles and detected using REMPI and VMI.
• Figure 2: Energy-level diagrams illustrating the Zeeman shifts for S atoms in different states. Low-field-seeking states that can be selected by the decelerator are depicted in red, other states are shown in blue.
• Figure 3: Selected parts of TOF profiles for S($^1D_2$) atoms exiting the Zeeman decelerator operated in hybrid mode. The measured and simulated profiles are shown in blue and red, respectively. The measured (black) and simulated (gray) profiles obtained when the solenoids are not pulsed are shown for comparison. The experimental profiles are normalized with respect to the profile obtained with the solenoids switched off (black).
• Figure 4: Experimental 1+1 REMPI spectrum for S($^1D_2$) atoms (a) and 2+1 REMPI spectra for S($^3P_{J=2,1,0}$) atoms (b) exiting the decelerator. The spectra in the top half (blue) were measured with the decelerator operated in hybrid mode, using a pulse sequence optimized for S($^1D_2$) atoms. The spectra in the bottom half (red) were measured with the solenoids switched off. The vertical black lines indicate the wavelengths for the resonant transitions to the excited states. All ground-state S-atom signals were measured with the same laser intensity. For clarity, the intensity of the peaks for $^3P_{1,0}$ is magnified 5 and 500 times, respectively.
• Figure 5: Selected parts of measured TOF profiles for S($^1D_2$) (blue) and S($^3P_2$) (red) atoms exiting the Zeeman decelerator, operated in hybrid (a) or deceleration mode (b), both with a mean forward velocity of 850 m/s. Each profile is normalized to its peak intensity to facilitate comparison. Simulated TOF profiles for S($^1D_2$) are shown in (c) and (d), and for S($^3P_2$) in (e) and (f), corresponding to the experimental conditions in (a) and (b), respectively. The contributions of the low-field-seeking $m_J = 1$ and $m_J = 2$ states to the simulated profiles are indicated by dashed and dash-dotted lines, respectively.