Hydrogen bond network structures of protonated 2,2,2-trifluoroethanol/ethanol mixed clusters probed by infrared spectroscopy combined with a deep-learning structure sampling approach: the origin of the linear type network preference in protonated fluoroalcohol clusters.

While preferential hydrogen bond network structures of cold protonated alcohol clusters H(ROH) are generally switched from a linear type to a cyclic one at = 4-5, those of protonated 2,2,2-trifluoroethanol (TFE) clusters maintain linear type structures at least in the size range of = 3-7. To explore the origin of the strong linear type network preference of H(TFE), infrared spectra of protonated mixed clusters H(TFE)(ethanol) ( + = 5) were measured. An efficient structure sampling technique using parallelized basin-hopping algorithms and deep-learning neural network potentials is developed to search for essential isomers of the mixed clusters.

Hydrogen bond network structures of protonated dimethylamine clusters H(DMA) ( = 3-7).

Infrared spectroscopy of protonated dimethylamine clusters, H(DMA), ( = 3-7), and their Ar-tagged clusters was performed in the NH and CH stretching vibrational region to explore their hydrogen bond network structures. A stable isomer search and vibrational spectral simulations of the clusters were also carried out to support the interpretations of the observed spectra. Weakly hydrogen-bonded NH stretching vibrational bands, which are characteristic of cyclic structures of small-sized protonated clusters, are observed in the spectra of the Ar-tagged clusters of ≥ 5, while only linear chain type structures are suggested for the Ar-tagged clusters of = 3-4 and the bare clusters of all the sizes.