Conformational Landscape of the 1/1 Diacetyl/Water Complex Investigated by Infrared Spectroscopy and ab Initio Calculations

Abstract

The complexes of diacetyl with water have been studied experimentally by Fourier transform infrared (FTIR) spectroscopy coupled to solid neon matrix and supersonic jet, and anharmonic ab initio calculations. The vibrational analysis of neon matrix spectra over the 100-7500 cm -1 infrared range confirms the existence of two nearly isoenergetic one-to-one(1/1) diacetyl-water S 1 and S 2 isomers already evidenced in a previous argon matrix study. A third form (S 3 ) predicted slightly less stable [D. Dargent et al. , J. Mol. Mod. 21, 214 (2015)] is not observed. The correct agreement obtained between neon matrix and anharmonic calculated vibrational frequencies is exploited in several cases to derive band assignments for the vibrational modes of a specific isomer. Thereafter, theoretical x ij anharmonic coupling constants are used for the attribution of combination bands and overtones relative to the 1/1 dimer. Finally, the most stable isomer of the one-to-two (1/2) diacetyl-water complex is identified in the OH stretching region of water on the grounds of comparison of experimental and calculated vibrational shifts between water dimer and the three most stable 1/2 isomers. I -IntroductionIt is now well established that non-covalent interactions such as hydrogen bonds involved in small hydrated clusters play an essential role in atmospheric chemistry, astrophysics and also in many biochemical and catalytic processes.1 Since the pioneering spectroscopic works about the enthalpy and the hydrogen bridges in crystallographic structures such as ice and liquid water, 2,3 many advanced experimental methods were developed in the last thirty years to interpret the bulk water structure and dynamics. In this context, the spectroscopic study of small water clusters produced at very low temperature in nearly isolated conditions proved to be determinant for improving the building of reliable intermolecular potential energy surfaces based on a back and forth procedure between experiment and theory. As a first step toward this objective, we can cite the challenging studies based on jet-cooled far-and near-IR laser and microwave spectroscopy which yielded new insights into the tunneling motions of the water dimer 4-6 and allowed to determine a polarisable water pair potential. 7The huge capacity of water to establish hydrogen bonds with the close environment owing to its twice role of hydrogen-bond donor and acceptor would suggest to use a molecular approach based on a step by step increase of the size of hydrates for most studies related to the hydration process of organic species. It has been shown in many previous solid 8 and gas phase studies 9-11 that very different structural architectures of hydrated organic In the following we reported a series of experiments mainly achieved in solid neon and at a least degree in the supersonic expansion of the Jet-AILES facility on the infrared beamline of the SOLEIL synchrotron. Previous studies realized in our group about the characterization of small hydrated complexes highlight...

Vibrational study of acrylonitrile dimer and acrylonitrile-water hydrogen-bonded complexes in solid neon supported by ab initio calculations

“…Indeed in the 1:1 complex the water molecule is the proton donor as a water molecule in the water dimer and in this case the X 23 anharmonicity coefficient for the  2 + 3 combination is -17.6 cm -1 [20]. Remark is supported by the comparison with results for other hydrogen bonding complex [13][14][15]27] for which the X 23 coefficient values are similar to that of the water dimer within a few cm -1 . Taking into account the water dimer X 23 coefficient value and calculated shift values, we can exclude the AW3 isomer because the combination value will be too high.…”

Study of diacetyl-water clusters using Raman scattering and theoretical calculations

“…Now, it has been established that noncovalent interactions, in particular hydrogen bonding, play an important role in atmospheric chemistry, astrophysics, as well as many biochemical and catalytic processes [1][2][3]. 1,2-butadione or biacetyl are other names for diacetyl (DA) [4][5][6][7][8].…”

“…1,2-butadione or biacetyl are other names for diacetyl (DA) [4][5][6][7][8]. Dargent et al [1] studied two different S1 and S2 isomers of the diacetyl-water system by FTIR spectroscopy in a neon matrix and by anharmonic ab-initio calculations, and determined that the O-H stretching vibration was the most stable for the diacetyl-water system. Because, it causes an increase in the amount of carbosol in the atmosphere, DA in the gaseous phase has been studied in the far and near IR regions (25-600 cm −1 and 520-6500 cm −1 ) [5].…”