Formation and rearrangement of HCCF⋯HF complexes after CF2CH2 photolysis: A matrix isolation and <i>ab initio</i> study

Studies on the reactions between neighbors and rearrangements occurring in noble gas matrices in the same matrix cage at temperatures of a few kelvins may improve our understanding of intermolecular interactions, quantum-mechanical tunneling, and the effect of a medium on low-temperature processes. Here, we present experimental evidence of the rearrangement of HCCF⋯HF complexes taking place in solid Ar at 5.5 K. The complexes were obtained by 193 nm photolysis of CF2CH2 matrix-isolated precursors and characterized on the basis of CCSD(T) computations and available literature data. The absorption bands, which remain virtually unchanged during the argon matrix standing in the dark at 5.5 K after photolysis (set III), were attributed to the T-shaped HCCF⋯HF complex (π-complex), while those observed to increase (set I) were assigned to the "hockey-stick"-shaped FCCH⋯FH complex (FH-complex). The decrease in another group of absorption bands (set II) was found to negatively correlate with the growth of I, indicating II → I rearrangement. The speed of the process is roughly the same in the 5.5-6.5 K region and dramatically increases at higher temperatures. Set II was attributed to the L-shaped complex of the FCCH⋯FH geometry stabilized by a matrix (outlined here as point L). No similar transformations were observed in solid Ne, Kr, and Xe, making this process a remarkable example of a matrix-specific rearrangement.