Infrared vibrational spectra of matrix-isolated cyclic Li2F2, Li3F3, and Li4F4 isotopomers

Infrared (IR) spectra of the 6,7Li isotopomers of the LiF species isolated in rare gas matrices are interpreted with the input of molecular geometries and vibrational spectra computed using ab initio molecular orbital (MO) theory at the MP2/6-31G* level. The MO computations, together with IR matrix-isolation observations, support firm species assignments and vibrational assignments for the IR-active modes of the title molecules. The study presents the first evidence for the existence of matrix-isolated Li4F4 cyclic tetramer, and resolves contradictory species/vibrational assignments for the smaller oligomers. Most of the matrix-isolated cyclic trimer and tetramer population is formed by coalescence of smaller species during the matrix deposition process or during subsequent matrix annealing/warming processes. There appears to be no evidence in the available matrix-isolation data for the existence of a matrix-stabilized Li2F2 linear dimer.