Pyridine Dimers and Their Low‐Temperature Isomerization: A High‐Resolution Matrix‐Isolation Spectroscopy Study

The bonding between two neutral aromatic compounds, especially small ones, has been controversially debated in the last decades, and terms like “π-stacking” had to be revised. Surprisingly, despite of many experimental computational work, there is still no clear consensus about structure pyridine dimer. In this for different isomeric forms dimer, structures were elucidated by combining high-resolution matrix-isolation spectroscopic results with quantum-chemical calculations. High-resolution IR spectra Ne matrices at 4 K containing recorded concentrations upon annealing 10 12 K, relying on three isotopologues pyridine. show presence hydrogen-bonded, T-shaped, stacked weakly-bound dimers. Among these, hydrogen-bonded isomer identified as lowest-energy form. provide first time conclusive information interaction