A temperature-dependent hydrating water structure around chlorine anion

A temperature‐dependent hydrating structure around SO42− investigated from Raman spectroscopy

“…Through comparing the SC OD/OH stretch bands for Na 2 SO 4 and those for NaCl previously reported 25 (Figure 1), we can find similar band profiles for the two solutes, but the relative intensities of PK 1 (to PK 2) on the Na 2 SO 4 -correlated bands are generally higher than those on the NaCl-correlated bands at the same temperature. The temperature marking the sinking of the SC OD stretch band for Na 2 SO 4 is close to that for NaCl around 473 K, and this temperature is $513 K for Na 2 SO 4correlated and $473 K for NaCl-correlated OH stretch bands.…”

“…Essentially, it is the widespread HB interactions that make the OD/OH stretch band to be a broad, asymmetric, and multimode contour. 26 As analyzed from the OH stretch bands of H 2 O up to 753 K, 18 19,27 and D 2 O(H 2 O)ÀNaCl 25 up to 573 K by our previous studies, water tends to have a structure with different HB configurations. We classify the five main HB configurations in water as two tetrahedral, single donor (SD) where a water molecule forms hydrogen bonds with only two neighbors, single hydrogen-bonded water (SHW) who possesses only one donor/acceptor, and free water (FW) without any hydrogen bonds (see Hu et al 19 for more details about the classification).…”

“…This approximate description of the structure details in water is essentially consistent with those by previous studies. 8,9,28 As seen from Figure 2, we use this classification scheme to interpret the OD/OH stretch F I G U R E 2 A sketch showing the classification on the hydrogen bonding configurations in water, and the assignment of the Gaussian-fitting components (C1 $ C5) (from Hu et al 25 ). Note that the total spectral line approximately represents the OD/OH stretch band profile at ambient conditions and so the wavenumber values for the abscissa axis are not shown.…”

“…The SC OD/OH stretch bands of NaCl have been attributed primarily to water in the Cl À hydration shell, 25 because the effect of Na + on the OD/OH stretch bands of water is negligible. 20,29 Similarly, we assign the SC OD/OH stretch bands of Na 2 SO 4 to hydration water around SO 4 2À .…”

“…Based on the classification on the HB configurations in water and the Gaussian-fitting analysis on the SC OD/OH stretch bands of NaCl, 25 we decompose the SC OD/OH stretch bands of Na 2 SO 4 into four Gaussian components centered at 2395/3245 cm À1 , 2500/3420 cm À1 , 2550/3500 cm À1 , and 2660/3635 cm À1 and assign them to OD/OH stretch vibrations engaged in tetrahedral, SD, SHW, and FW (HB) configurations, respectively (Figure 3). In fact, these four components coincide with C2 $ C5 shown in Figure 2 2À hydration shell (Figure 4b).…”