Far infrared spectra of (HF)2and (HF)3in solid argon

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Abstract
Hydrogen fluoride dimers and trimers have been examined by Fourier transform infrared spectroscopy down to 80 cm-1 in solid argon samples. A weak new 128 cm-1 absorption followed the 189 and 400 cm-1 (HF)2 bands on annealing and is assigned to the hydrogen bond stretching fundamental in solid argon. A similar 124 cm-1 band was associated with 162 and 300 cm-1 (DF)2 bands on annealing and is assigned to the deuterium bond stretching fundamental. This assignment is in agreement with very recent potential surface calculations and deductions (125 ± 5 cm-1) from other gas phase absorption of (HF)2. A sharp new 152·5 cm-1 band was associated with the 446 and 560 cm-1 (HF)3 bands on annealing and is assigned to the antisymmetric hydrogen bond stretching fundamental in cyclic (HF)3 in solid argon. The blue shift to 155·5 cm-1 for cyclic (DF)3 provides evidence of slightly stronger deuterium bonding in the cyclic trimer.