Noncovalent Interactions
Noncovalent interactions play an important role in many fields of chemistry, such as protein-folding or molecular recognition. They are also known to govern the low-temperature behaviour of chemical reactions, where the presence of a noncovalent prereactive complex can lead to increasing reactivity at lower temperatures. These types of reactions are extremely important in cold regions of the Universe, such as molecular clouds, from which stars and planets form, or exoplanetary atmospheres.
Data Deficiency
However, detailed theoretical and experimental data is missing for a large class of astronomical relevant molecules. A prominent example are polycyclic aromatic hydrocarbons (PAHs), which are among the most complex and abundant organic molecules detected in space to date, but whose abundance is dramatically underestimated by current chemical models. A likely reason for this is that several important formation routes for PAHs are missing in these models.
Exothermic Reactions
Researchers from HFML-FELIX have now studied the reaction between the benzonitrile cation and acetylene in detail by mass-spectrometry and infrared action spectroscopy using the FELIX infrared free-electron lasers. The in situ spectroscopic probing, aided by quantum-chemical calculations, revealed the presence of a noncovalently bound prereactive complex in the first reaction step, followed by the formation of polycyclic molecules consisting of multiple fused rings upon the addition of a second acetylene.
The reactions were found to be exothermic and barrier-less, and provide efficient formation routes for complex aromatic species under interstellar and planetary atmosphere conditions. The isolation and spectroscopic characterization of the noncovalently bound prereactive intermediate complex highlights the so-far widely neglected role of noncovalent interactions in cold ion-molecule chemistry.
