The Chemistry of the Cosmos
Emma Lewis | 27 March 2017

Classical chemistry rules dictate that certain molecules that exist in outer space should not exist. So how can we explain their presence and how are they formed?

 

Interstellar space is cold: it can reach temperatures as low as 3 Kelvin (-270°C). So cold, that for most chemical reactions there is not enough energy to break the bonds required to form new molecules, and so as temperature decreases so does the rate of reactions.

 

However, there are a host of organic complex molecules in space. Any molecules that simply drift past each other do not have the energy to interact. A grain of cosmic dust could unlock part of the answer; molecules can stick to the surface of the dust grain, giving them enough time to gain the energy needed for the reaction.

 

Around 600 light years from earth resides the Perseus molecular cloud. Recently, methoxy molecules (containing carbon, hydrogen and oxygen) were detected within it which baffled researchers who were not able to create the molecule in a lab using cosmic dust and the basic reactants. It is possible to create methoxy by combining a hydroxyl radical (which has an unpaired electron) and methanol gas. Whilst these substances are both present in space, the cold expanse simply does not contain enough energy to hurdle the significant energy barrier required for the reaction.

 

It seems that Quantum mechanics may hold the answer. Quantum tunnelling allows methoxy to be formed at around 63 Kelvin (-210°C) and whilst most interstellar regions are much colder than this, dust clouds near to stars are able to reach these kind of temperatures. Negatively charged electrons are held in atoms by the attractive force of the positively charged nucleus. Classical physics dictates that the electron can only escape from the nucleus when it hurdles the nucleus’ ‘potential barrier’ and thus overcomes the attractive force. Quantum tunnelling is the idea that instead of going over the energy barrier, there is a very small chance that the electron could tunnel through it. Imagine a ball trying to roll over a hill – if it does not have enough energy, then it will not get over it and a reaction will not take place. However, if the ball simply breaks though the barrier then less energy is required as it does not need to go over the hill – simply through it.

 

Whilst at room temperature the molecules just collide off each other, when the temperature is reduced the molecules interact with each other for longer due to their relatively slow speed. This gives a greater opportunity and increases the likelihood that quantum tunnelling will occur. It seems that interstellar space could hold a host of chemical reactions which we hadn’t even considered possible.

James Routledge 2016