AbstractThe Raman spectra of the three crystalline modifications of eight isotopic species of methyl ammonium chloride and their isotopic solid solutions have been recorded in the temperature range 70–300 K. The CH3 and NH bands in the hydrogen stretching region of the spectra have been identified and an assignment of the CH3 bands is proposed. The large number of methyl bands in the CH stretching region is explained as the result of strong coupling of the symmetric hydrogen stretching fundamental and overtones of the CH3 bending fundamentals. Correlation and crystal field splittings of the bands are also discussed.