Mechanochemical reaction between the probe and the matrix:: A possible source of errors when IR spectra of alkali acid bifluorides are recorded in alkali halide pressed disks

The mechano-chemical reactions of alkali acid bifluorides (MHF2), with alkali halides (MX), were studied by x-ray diffraction (XRD) and IR spectroscopy. The reactions were carried out by milling the solid reagents in equimolar ratio by hand in an agate mortar. LiHF2 is unstable on milling and decomposes to LiF and HE . Rb, Cs, and NH4 acid bifluorides react KBr leading to the corresponding bromides and stable KHF2. Similar reactions are observed with Na halides, leading to NaHF2. NaHF2 reacts with KF to form KHF2 and NaF. The mechano-chemical reactions with alkali halides are considered in connection with the use of alkali halides as matrices for IR spectroscopy.