Temperature dependence of the ν s(OH) band shape of ortho-Mannich bases in gas phase and liquid xenon solution

Abstract

Infrared spectra of the two ortho-Mannich bases 2-( N, N-dimethylaminomethyl)-4-chlorophenol ( I) and 2-( N, N-dimethylaminomethyl)-4,6-dichlorophenol ( II) with a medium-strong intramolecular hydrogen bond, were measured in a wide frequency (4000-50 cm −1) and temperature (−105°C to +120°C) range in liquid Xe, CCl 4 solutions and gas phase. The temperature studies of the first and second spectral moments of the ν s(OH) band in liquid Xe within the temperature range from −105 to +30°C allow for the analysis of the ν s(OH) mode coupled with the low-frequency vibrations (ν l ) of the non-linear hydrogen bond. Transitions located at ca. 150, 250 and 340 cm −1 were selected as such ν l modes. The effective coupling parameter between high-frequency ν s(OH) and low-frequency ν l vibrations of the hydrogen bridge was evaluated: b = α ssl /ω l ⋍ 0.7. Model calculations accounting for the hot and combination transitions give satisfactory reproduction of the gas phase ν s(OH) and ν s(OD) bands shapes. Both temperature experiments and model calculations predict that even at 0 K the halfwidth of the ν s(OH) band can be quite large, viz. ca. 200–400 cm −1.