Infrared-optical double resonance spectroscopic measurements and high level ab initio calculations on a binary complex between phenylacetylene and borane-trimethylamine. Understanding the role of C-H center dot center dot center dot pi interactions

The structure of the binary complex between phenylacetylene and borane-trimethylamine has been elucidated using IR-UV double resonance spectroscopy in combination with high level ab initio calculations at the CCSD(T) level. Borane-trimethylamine interacts primarily through multiple C-H center dot center dot center dot pi interactions with the p electron density of the benzene ring in phenylacetylene. CCSD(T) level calculations provide reliable estimates for the interaction energy and free energy, which are in accord with the experimental observations. The DFT-SAPT calculations point out that the dispersion interaction plays a major role in the formation of the experimentally observed complex, along with a sizable contribution from electrostatics.