Temperature dependence studies and model calculations of ν(OH) and ν(OD) band shapes of salicylaldehyde

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Abstract IR spectra of salicylaldehyde (OH and OD) have been studied over a wide temperature range in teh vapor phase, liquid Xe solution and Ar matrices. Far IR and Raman spectra have been obtained. Ab initio calculations at the 3-21G∗∗ level have been performed in order to establish the geometry of the molecule, normal coordinates and frequencies of vibrations. It has been found that profiles of both ν (OH) and ν (OD) bands are formed by the fundamental transition ν s , by the weak sum transition ν s + ν 3 , where ν 3 = 264 cm −1 is an in-plane vibration involving deformation of the chelate ring with significant stretching of the intramolecular H-bond, and by a series of hot transitions from levels of ν 3 and other low frequency modes ( ν i ) of the chelate ring. The ν (OH) profile is perturbed additionally by several Fermi resonances with overtones and combinations of bending vibrations δ(OH). Anharmonicity constants, which characterize coupling of ν s with ν i and δ(OH), have been derived from the temperature dependence of the first spectral moments of the bands, using the results of the 3-21G∗∗ treatment. Model calculations of ν (OH) and ν (OD) band shapes have been performed.