- Acids behave quite differently in dense interstellar clouds.
- The study addresses a basic question of chemistry: whether acid can dissociate in extreme temperatures.
- The answer is both ‘yes’ and ‘no.
Things behave differently in interstellar space compared to planetary conditions. This is where extremely low temperatures (less than 10 K) govern the chemistry of icy dust grains.
Recently, a research team at the Ruhr-University Bochum, Germany, analyzed how acids interact with molecules of water at extremely high temperatures and low pressures like those found in interstellar space.
Researchers analyzed whether HCl (hydrochloric acid) can donate a proton, or alternatively, form a covalent bond with an electron pair in interstellar space. And they found an interesting answer – it is both yes and no, depending on the order in which water and HCl molecules brought together.
What Happens When HCl Is Added To Water?
Under room temperature and pressure, HCl (strong acid) dissociates quickly after coming into contact with water molecules. The acid ejects its Hydrogen ion (proton), forming a hydronium cation (H3O+) and chloride anions (Cl-).
But what if the process takes place in interstellar space. Would the same acid-alkali chemistry apply to such extreme conditions? Researchers tried to find the answer, which could eventually help them better understand how complex molecules formed in space.
They created interstellar-like conditions in the lab and monitored all processes using an advanced technique called infrared spectroscopy. It is used to capture tiny vibrations of molecules and identify and study chemicals.
The high-intensity pulsed free-electron lasers were used to carry out measurements in the infrared fingerprint region. Using computer simulations, the team then interpreted experimental outcomes.
In artificial conditions, the team added four molecules of water (one-by-one) to the HCl molecule. The acid dissociated immediately, donating its proton to a water molecule and forming a hydronium ion. The remaining hydronium ion, chloride ion, and the other three molecules of water formed a cluster.
However, when researchers converted water molecules into an ice-like cluster before adding them into the HCl, they got a completely different outcome. The acid didn’t dissociate, as hydrogen ion and chloride ion remained bonded with each other.
This indicates that hydrochloric acid doesn’t necessarily have to dissociate in ultracold ‘stardust conditions’. The same holds true for other acids as well, which represents the fundamental principle of chemistry in interstellar space.
The findings show that ‘dissociation’ and ‘no dissociation’ are just two sides of the same coin. In extreme stardust conditions, the mixing ratio of molecules is not the only thing that matters, but also the order in which compounds are being added to each other.
This phenomenon can be used in future studies and simulations under ultracold environments.