Our research group is generally interested in working with exotic radioactive molecules to search for sources of new physics beyond the standard model. To this end, the bent molecular ion RaSH+ holds much discovery potential. We describe below how we produce cold and trapped RaSH+ in our ion trapping system.
Instructions for synthesizing H2S for synethsizing RaSH+ via the reaction
H2S + Ra+ ⟶ RaSH+ + H.
Warning: The following chemistry should be done with plenty of care. H2S is highly toxic even in small quantities.
This video explains how to make H2S, and is what we followed to develop our procedure.
2x Ring Stand
2x Synthware™ 90 degree vacuum adapter with glass stopcock
1x 50 mL graduated cylinder
1x Long glass straw (any tube to get gaseous H2S to the bottom of the graduated cylinder.)
2x CF Valve
3/8 in tubing and 1/4 in tubing
100 g Copper Sulfate Penta Hydride
30 mL 37% HCl
30 g Iron(II) Sulfide
Argon gas cylinder
- Put one H2S detector in the fume hood, and a second outside of the fume hood.
- Fill a graduated cylinder with 50 mL of DI water. Put 21 g of CuSO4 into the graduated cylinder. Stir the solution until saturated.
- Put 5 g of FeS into the three-neck flask using a funnel.
- Make sure that the addition funnel valve is closed, and replace the funnel from the previous step with the addition funnel.
- Add 10 mL of saturated HCl into the addition funnel. This amount of HCl is estimated to make 1-2 L of gaseous H2S.
- Place the base of the three neck flask in an ice bath. We do this to cool the HCl during the reaction so that HCl vapor is produced in smaller quantities relative to H2S than without an ice bath.
- Close the valve connecting the three-neck flask with the CF valves, and open the valve connecting the argon to the three-neck flask.
- Disconnect the argon hose and turn the argon valve on the cylinder to provide a gentle argon flow. Test for flow through the hose. Reconnect the hose and run argon through the three-neck flask with no cap on the addition funnel for about a minute. After that, turn off the argon and put the cap onto the addition funnel without a keck clamp, this is important as the cap (without a clamp) can release any excess pressure.
- Make sure that the CF valves are open, and open the valve connecting the three-neck flask to the CF valves. Turn on argon until the system is entirely flushed.
- Turn off argon, and close the valve connecting the three-neck flask to argon.
- Open the addition funnel valve slowly to introduce HCl into the three-neck flask to react with FeS. You should see bubbles in the CuSO4 solution, and after a ~minute black precipitate will form in the solution. Close the addition funnel valve, and when bubbles are no longer forming, close off the two CF valves simultaneously. Take the glass cap off of the addition funnel.
- Undo the KF connections around the two CF valves.
- Blow out residual H2S in the two CF to KF connectors with N2. The CF valves now contain H2S between them and may be removed from the fume hood for use with UHV experiments.
- Open all valves on the three-neck flask and leave the addition funnel valve closed. Remove the cap on the addition funnel and flush with N2.
- Pour residual HCl from the addition funnel into the HCl waste bottle and dilute with water.
- Add water through a funnel into the three-neck flask, and pour the solution into another waste bottle.
- Pour the CuSO4 solution (with precipitate) into a separate waste bottle.
- Clean all glassware.
Instructions for making RaSH+ by leaking H2S gas into the vacuum chamber where Ra+ is being laser-cooled in our ion trap.
3x CF valves
1x 1.33 in CF "T"
1x 1.33 in CF blank
1x CF 1.33 to KF16 converter
1x slow leak valve
1x Turbo Pump
KF16 tubing
CF 1.33 in tubing
- By following the previous procedure, we were able to securely store ~50 cm3 of H2S gas between two closed CF valves (blue square in the image above). With the valves still closed, remove the CF to KF converters on either end of the CF valves from the H2S production procedure.
- On one end of the CF valves, bolt on a 1.33 in CF blank. On the other end, bolt on a 1.33 in CF 'T' piece.
- Working on the 'T' piece, attach one open end of the 'T' to a CF valve, and the other end of the 'T' to a CF tube connected to the slow leak valve on the ion trap vacuum system. Then, using a CF to KF converter, attach KF16 tubing to the new CF valve, and connect the other end of the tube to a turbo pump.
- With the leak valve closed, and the H2S CF valves closed, open the CF valve that connects to the turbo pump. Turn on the turbo pump, and pump down the system until pressure is around 1x10-4 mbar.
- Close the CF valve to the turbo pump, and turn off the turbo.
- Open the CF valve that connects the CF 'T' and the precision leak valve. There should now be a throughline for the H2S to get to the leak valve on the trap. The H2S pressure will depend on the length of the CF tube used, but should be at least a factor of 5 less than 1 atm.
- Trap Ra ions. Then, by slowly opening the precision leak valve, introduce H2S into the trapping volume. Look for gas collisions on the imaging CCD and wait for a dark ion to be produced. Use OMS to confirm RaSH+ is the dark ion.
We use Optical Mass Spectrometry (OMS), which can realize sub-dalton resolution, to identify dark ions in our trap. https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.126.023002
Figure: An illustration of OMS on a dark molecular ion trapped between 2 "bright" Ra+ ions.
We begin with a chain of 2 or 3 Ra+ ions. Then, we leak in H2S gas (using the procedure above) and wait for one of the ions to go dark (depicted as a black box with a question mark in the figure above). We change the detuning of either our 1079 nm Ra+ repump laser, or the 468 nm Ra+ cooling laser, which results in "local heating" and "global cooling" that causes our ion chain to oscillate axially in the trap at a secular frequency of the trapped ions.
When an ion goes dark, we immediately perform OMS and record an FFT of the axial oscillation frequency. We continue to do this periodically, (about every 5 minutes), in order to check if there has been any drift of the axial frequency. We monitor the dark ion until it dissociates, and as soon as the dark ion dissociates, we perform OMS on the the chain of bright ions. We use the data from the post-dissociation OMS FFT to calibrate the final dark ion OMS FFT, and end up with the following plot:
This data confirms that we a trapped dark ion made from radium and H2S which has a mass of about 259 amu, equal to 226+33 (Ra = 226 amu, SH = 33 amu). This confirms RaSH+ synthesis!