Raman study of vibrational dephasing in hydrogen-bonded binary and ternary complexes of C6H5Cl and methanol

The shifts and linewidth changes of three vibrational modes of C6H5Cl were studied in hydrogen-bonded binary mixtures C6H5Cl+CH3OH at various mole fractions of C6H5Cl, C=0.05, 0.1, 0.2, 0.3, 0.5, 0.7 and 0.9. The study reveals that the phenomena of motional narrowing and diffusion play simultaneous roles in the dephasing of the ring breathing and trigonal bending modes at ∼1000 and ∼1024 cm−1, respectively. Minima at C=0.7 and 0.2 in the ΓL versus C plot are explained by the formation of hydrogen-bonded dimer, C6H5Cl⋯HOCH3, and trimer, C6H5Cl⋯(HOCH3)2, complexes. The dephasing of a third mode at ∼700 cm−1 is explained using the indirect dephasing model of Fischer–Laubereau.