How a Silver Ion Traps Oxygen in a Trap express
In the cold, sparse clouds of space, particles rarely meet, but sometimes an ion and a neutral molecule pass close enough to stick together. As they do, they emit light, like a muted flash carrying away excess energy. This process is called radiative association, and it is responsible for the formation of many molecules in interstellar space.
Measuring such a union in the lab is tough: you need to keep particles together for a very long time without letting them fly apart. The new device does exactly that. Silver ions and oxygen molecules are launched into a trap — a device that holds charged particles with electromagnetic fields, like invisible walls. The particles stay close for hours, and during that time some pairs manage to combine. The researchers tracked for the first time how the reaction rate changes at different oxygen pressures and estimated how quickly a silver ion captures an oxygen molecule.
Such an instrument is like a quiet dating room where rare pairs can finally meet. It will allow measuring the rates of union for various ions and molecules found in cosmic clouds. Understanding these processes will help explain where complex molecules in the cold corners of the universe come from and how they influence the birth of stars and planets.
Original abstract
as written by the authors arXiv:2601.09862
The ability to directly measure radiative-association rate coefficients for reactions between ions and neutral molecules has long challenged chemical physics laboratories, yet radiative association is one of the most important processes occurring in cold, diffuse regions of space. A reaction kinetics instrument has been developed for the investigation of ion--molecule radiative-association reactions, aimed at measuring slow, effective reaction rate coefficients for species relevant to astrophysical objects. The instrument consists of a glow-discharge ion source for production of bright and stable ion currents, a quadrupole mass filter for mass selection and detection, and a quadrupole ion trap capable of trapping reactants and products for the long times needed to measure slow kinetics. The performance and adaptability of the glow-discharge ion source has been evaluated using several configurations. To assess the feasibility of measuring reaction rate coefficients, the reaction of Ag$$^{+}$$ and O$$_{2}$$ was studied under pseudo-first-order conditions in the ion trap at room temperature. We present the first pressure-dependent study of this reaction and extract a lower limit of $$1 \times 10^{-15}$$ cm$$^3$$ molecule$$^{-1}$$ s$$^{-1}$$ for the Ag$$^{+}$$ + O$$_{2}$$ effective radiative-association rate coefficient. Measurements of effective radiative-association rate coefficients are possible for diverse atomic and molecular ions that react with neutral molecules over a range of rates in this versatile new instrument.
In interstellar space, the density of matter is so low that there is less than one atom per cubic centimeter, so reactions proceed extremely slowly — sometimes a single collision takes years.