Understanding Pressure‐Induced Polymerization of Carbon Monoxide at Molecular‐Level: A Quantum Chemical Investigation of Oligomerization of ( CO ) n ( n  = 2–6)

ABSTRACT Oligomerization of (CO) n ( n = 2–6) clusters initiated by mechanical pressure has been investigated using quantum chemical methods at TPSSTPSS‐D3/aug‐cc‐pVTZ level. The clusters were confined within He@60 (for dimer) and He@180 cages (for trimer to hexamer), and mechanical pressure up to 18.9 GPa was exerted on the clusters by gradually decreasing cage volume. A total of 29 distinguishable conformers, 2, 4, 10, 11, and 2 for dimers, trimers, tetramers, pentamers, and hexamers, respectively, have been studied. Dimerization was found to initiate at a considerably higher pressure of 18.9 GPa, compared to the larger clusters at ≤ 1.6 GPa. Ten distinct and stable oligomers were obtained bound by a variety of covalent linkages (CC, CC, CO, CCO, CCC, COC, etc.), all of which have been experimentally identified. Atom in molecules analyses have been used to confirm the formation of all covalent linkages in the formed CO oligomers.