Infrared Spectrum of LiF, Li2F2, and Li3F3 by Matrix Isolation

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Abstract
The infrared spectrum of the vapor species above lithium fluoride has been examined in the frequency range 4000–200 cm−1 using the matrix isolation technique. The spectrum is interpreted in terms of monomer, dimer, and trimer molecules. Isotope shifts are consistent with a planar cyclic configuration for the dimer. The 7Li dimer has the following infrared-active fundamentals: v(B3u)=655 cm−1, v(B2u)=570 cm−1, and v(B1u)=300 cm−1. The remaining infrared-inactive frequencies of the dimer are estimated at v(Ag)=560 cm−1, v(Ag′)=280 cm−1, and v(B1g)=490 cm−1. The following frequencies are tentatively assigned to the infrared active fundamentals of the 7Li trimer, 230, 267, 509, and 736 cm−1.