https://phys.org/news/2018-07-power-molecular-mystery.html

But this is often not the case in practice. Molecular reactions frequently behave differently. Optimal conditions are often not present, like with water molecules used in hydrogen production, and this makes reactions challenging to investigate, even with computer simulations.

Until recently, scientists haven't known what initiates the splitting of water molecules. However, it is known that a water molecule has a lifespan of 10 hours before it splits. Ten hours may not sound like a long time, but compared to the molecular time scale—a quadrillionth of a second—it's quite long. This makes it super-challenging to determine the mechanism that causes water molecules to divide. It's like looking for a needle in a haystack.