Temperature controlled microjets for liquid ammonia solutions

In 2019, Buttersack et al. demonstrated that liquid ammonia microjets can be studied by photoelectron spectroscopy. The apparatus they developed enabled scientists to examine solutions of cooled, condensed gases of any kind in vacuum. Although the runtime of the microjet was excellent, the device was limited by its unreliable starting procedure.

The authors have now improved upon their previous design and used it to study the release of liquid ammonia solutions in a vacuum through photoelectron spectroscopy.

To fix the startup procedure during initiation of the ammonia microjet and avoid clogging of the nozzle, the authors merged the micro nozzle directly with a micron filter. The device can run solutions while maintaining control over the temperature and concentration by using a proportional integral derivative feedback system which actively stabilizes the cryostat.

“Compared to the first experiments with liquid ammonia, the experimental design discussed here is much more reliable, as we overcame issues with initiating the microjet,” said author Tillman Buttersack. “We can control the concentration and temperature of the ammonia solutions so that we can compare the physical chemical properties of aqueous solutions to ammonia solutions under temperature-controlled conditions.”

They tested their experimental setup by measuring the valence binding energies of liquid ammonia at different temperatures and compared these for solvated electrons in liquid ammonia with aqueous solutions.

“This experimental setup enables to investigate solutions of condensed gases within a wide temperature range and therefore closes the gap between the well-studied aqueous solutions and cryogenic pure liquids,” said Buttersack.

Source: “Deeply cooled and temperature controlled microjets: Liquid ammonia solutions released into vacuum for analysis by photoelectron spectroscopy,” by Tillmann Buttersack, Philip E. Mason, Pavel Jungwirth, H. Christian Schewe, Bernd Winter, Robert Seidel, Ryan S. McMullen, and Stephen E. Bradforth, Review of Scientific Instruments (2020). The article can be accessed at https://doi.org/10.1063/1.5141359 .