Communication: Infrared spectroscopy of salt-water complexes

Tandy, Jonathan D.; Cheng, Feng; Boatwright, Adrian; Sarma, G.; Sadoon, Ahmed M.; Shirley, Andrew; Rodrigues, Natércia d. N.; Cunningham, Ethan M.; Yang, Shengfu; Ellis, Andrew M.

doi:10.1063/1.4945342

Cited by 25 publications

(42 citation statements)

References 21 publications

(37 reference statements)

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“…The spectrum in Figure 2d can only come from a complex with at least four methanol molecules and shows only very broad absorption features in the OH stretching region, extending from roughly 3100 through to 3400 cm −1 . A broad and largely structureless absorption in this region is also seen in the depletion spectrum recorded by detecting (CH 3 OH) 5 Na + (not shown here). We attribute the broadening in the OH stretching region to the presence of overlapping bands from multiple isomers for NaCl(CH 3 OH) 4 , as well as possible contributions from larger complexes owing to ion fragmentation.…”

Section: The Journal Of Physical Chemistry a Articlesupporting

confidence: 66%

“…Previously, we were able to record the IR spectrum of NaCl(H 2 O) by detecting Na + . 5 However, when H 2 O is replaced by CH 3 OH, there are no OH stretching features when detecting Na + (see the Supporting Information), and therefore, we conclude that ionization of NaCl(CH 3 OH) in a helium droplet leads to ejection of Cl but is not accompanied by CH 3 OH. Consequently, the IR spectrum of NaCl(CH 3 OH) must lie within the scan recorded by detecting (CH 3 OH)Na + , namely, Figure 2a.…”

Section: The Journal Of Physical Chemistry a Articlementioning

confidence: 71%

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Infrared Spectroscopy of NaCl(CH₃OH)_n Complexes in Helium Nanodroplets

et al. 2016

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Infrared (IR) spectra of complexes between NaCl and methanol have been recorded for the first time. These complexes were formed in liquid helium nanodroplets by consecutive pick-up of NaCl and CH 3 OH molecules. For the smallest NaCl(CH 3 OH) n , complexes where n = 1−3, the IR data suggest that the lowest-energy isomer is the primary product in each case. The predominant contribution to the binding comes from ionic hydrogen bonds between the OH in each methanol molecule and the chloride ion in the NaCl, as established by the large red shift of the OH stretching bands compared with the isolated CH 3 OH molecule. For n ≥ 4, there is a dramatic shift from discrete vibrational bands to very broad absorption envelopes, suggesting a profound change in the structural landscape and, in particular, access to multiple low-energy isomers. ■ INTRODUCTIONAlkali halides (MX) are archetypal univalent salts. The crystalline structure of the solid is disrupted by water, and these salts readily dissolve to form separated ions in dilute aqueous solutions. If the solid represents one extreme, then the counterpart is an isolated MX molecule. How might this smallest entity of salt, a single MX molecule, behave in the presence of a small water cluster, (H 2 O) n ? This problem can be addressed in experiments by forming isolated MX(H 2 O) n complexes and then using techniques, such as spectroscopy, to determine their properties. Such studies offer insight into the interaction between the constituent ionic particles and the solvent and can be reinforced through quantum chemical calculations. Understanding these interactions and the balance between them is critical in being able to carry out accurate simulations of bulk solutions. An early infrared (IR) spectroscopic study of a NaCl/H 2 O mixture in an argon matrix provided a tentative assignment of vibrational bands of the NaCl(H 2 O) complex.2 The first detailed spectroscopic study of several different NaCl(H 2 O) n complexes (n = 1−3) was obtained by microwave spectroscopy, and this revealed important structural information. 3,4 We have recently shown that complexes between NaCl and water molecules can be formed inside liquid helium nanodroplets, and this made it possible to record the first IR spectra of several small NaCl(H 2 O) n complexes. 5 The spectra for n = 1−3 are consistent with structures in which an ionic hydrogen bond (IHB) is formed between a single OH group in each water molecule and the Cl − in the salt. Evidence for interwater hydrogen bonding only begins to appear for n ≥ 4.An alternative solvent to water is methanol. Most solid alkali halides will dissolve in methanol, but their solubility is far lower than that in water. 6,7 The reduced solubility of salts in methanol when compared with that in water is a consequence of the hydrophobic (CH 3 ) group in the former. It would therefore be interesting to investigate how this amphiphilic character affects the interactions between a single salt molecule and one or more methanol molecules. It is well-known that...

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Section: The Journal Of Physical Chemistry a Articlesupporting

confidence: 66%

Section: The Journal Of Physical Chemistry a Articlementioning

confidence: 71%

Infrared Spectroscopy of NaCl(CH₃OH)_n Complexes in Helium Nanodroplets

et al. 2016

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“…Experiments were performed using a previously described helium nanodroplet instrument. [37][38][39] The nanodroplets were prepared by expanding helium gas at high pressure (32 bar) through the 5 µm diameter aperture of a cooled nozzle (16 K), resulting in a mean droplet size of ~5000 helium atoms. 34 The resulting continuous beam of droplets passed through a skimmer and into a cell containing AA vapor, where they could pick up one or more AA molecules.…”

Section: Methodsmentioning

confidence: 99%

Dimers of acetic acid in helium nanodroplets

Davies

Hanson‐Heine

Besley

et al. 2019

Phys. Chem. Chem. Phys.

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“…In response to the need of benchmark data for each type of ion pair, gas phase investigations have recently proven their ability to provide IR spectra of type-selected pairs by mass-and conformer-selective techniques. 7,8 While numerous charged ion pairs have been investigated in the gas phase, [9][10][11][12][13][14][15][16][17][18][19][20] spectroscopic studies on neutral ion pairs other than alkali halide systems 21,22 are rare in the literature. Following the pioneering work of Leone and co-workers in 2007, 23 an ion pair from an ionic liquid was characterised by its IR spectrum in the gas phase, first by helium nanodroplet isolation spectroscopy, 24 and by IR/UV double resonance spectroscopy.…”

Section: Introductionmentioning

confidence: 99%