Variations of bite angle and coupling patterns in double hydrogen bonds: The case of oxime dimers

Dimers of ketoximes are shown to represent intermediate cases of hydrogen bond-induced vibrational energy redistribution after OH stretching excitation. It is faster than in α-hydroxyester or alcohol dimers but slower than in carboxylic acid dimers. For this purpose, supersonic jet FTIR and Raman spectra of free and Ar-nanocoated acetoxime monomers, dimers and trimers are presented. By comparison to heated nozzle cyclohexanone oxime spectra, to condensed phase data and to quantum chemical calculations, a Fermi resonance description of the OH stretching dynamics in the symmetric, doubly hydrogen-bonded dimers is obtained. CN stretching and librational OH bending modes are predicted to participate in the coupling. Hydrogen bond topologies and cooperativity issues in larger oxime clusters are discussed.