Pressure tuning spectroscopy of the low-frequency Raman spectrum of liquid amides

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Abstract
The effect of hydrostatic pressure up to 4 kbar on the low frequency Raman spectrum of hydrogen bonded (formamide, N-methylformamide, N-ethylformamide, and N-methylpropionamide) and nonhydrogen bonded (N,N′-dimethylformamide and N,N′-dimethylacetamide) liquid amides is reported. A shift of ca. 4.0 cm−1/kbar is observed for the nonhydrogen bonded amides. For the hydrogen bonded amides the shift is ca. 2.0–3.0 cm−1/kbar. The difference may be explained by the compression of the hydrogen bond which affects the librational motion of the molecules.