Polarized FT-IR spectra of water in dodecylbutyldimethylammonium bromide monohydrate

Polarized infrared spectra of well-oriented crystalline thin films of dodecylbutyldimethylammonum bromide monohydrate (DBDM·H 2 O) were recorded in the region 5400-250 cm −1 . From the results of the polychroism measurements and the X-ray analysis, water bands were divided into three symmetry species ( A 1 , B 1 , and B 2 ). With the aid of frequencies and isotopic frequency ratios, the water bands were assigned to the three fundamental vibrations, two librations, and their overtones and combinations. In the crystalline environment, we have observed the doublets for each of the vibrationally isolated OH and OD stretching bands of HOD in isotopically diluted monohydrates DBDM·HOD. This spectral feature suggests the presence of two distinct configurations of the water molecule, one forming a strong and linear O 1 H ⋯ Br 1 hydrogen bond and the other forming a weak and slightly bent O 1 H ⋯ Br 2 hydrogen bond. The results in this work are discussed in connection with previous work. The OH stretcing bands in DBDM·H 2 O appear at higher frequency than in dodecylpropyldimethylammonium bromide (DPDM)·H 2 O or in DPDM· 1 2 H 2 O, while the HOH scissoring, rocking, and wagging modes occur at lower frequency. These are consistent with the weaker hydrogen bond of the water molecule and the longer O ⋯ Br hydrogen bond distance in DBDM·H 2 O than in the DPDM hydrates. Correlation between ν(OD) and the O ⋯ Br distance is also argued.