Rattling the cage: Micro- to mesoscopic structure in liquids as simple as argon and as complicated as water

Abstract

ÔØ Å ÒÙ× Ö ÔØThis is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Abstract. The water molecule has the convenient property that its molecular polarizability tensor is nearly isotropic while its dipole moment is large. As a result, the low-frequency anisotropic Raman spectrum of liquid water is mostly collision induced and therefore reports primarily translational motions while the far-infrared (terahertz) and dielectric spectrum is dominated by rotational modes. A C C E P T E D M A N U S C R I P T ACCEPTED MANUSCRIPTAtomic and globular-molecular liquids have a zero dipole moment as well as an isotropic polarizability tensor. These spectrum-simplifying properties were exploited in a study of a number of liquids and solutions using ultrafast optical Kerr-effect (OKE) spectroscopy combined with dielectric relaxation spectroscopy (DRS), terahertz time-domain spectroscopy (THz-TDS), and terahertz field-induced second-harmonic generation (TFISH) spectroscopy. For room-temperature ionic liquids (RTILs), liquid water, aqueous salt solutions, noble gas liquids, and globular molecular liquids it was found that, in each case, surprising structure and/or inhomogeneity is observed, ranging from mesoscopic clustering in RTILs to stretched exponential dynamics in the noble gas liquids. For aqueous electrolyte solutions it is shown that the viscosity, normally described by the Jones-Dole expression, can be explained in terms of a jamming transition, a concept borrowed from soft condensed matter studies of glass transitions in colloidal suspensions.

Structure and dynamics in protic ionic liquids: A combined optical Kerr-effect and dielectric relaxation spectroscopy study

“…40 Alternatively, in the frequency domain the sum of a number of Debye, damped harmonic (Brownian), or similar lineshapes are typically employed. 11,41 Here, there is no actual evidence of individual modes (with the exception of the weak shoulder in the OKE spectrum 5 close to 1 THz). A solution to this problem appeared with the PAN sample that proved to be a relatively good glass former.…”

“…6, 7 Femtosecond optical Kerr-effect (OKE) and dielectric relaxation spectroscopies are both highly sensitive 25 probes of low-frequency diffusional and librational motions. [8][9][10] By comparing OKE spectra with dielectric spectra (that cover a range extended to 10 THz, by combining dielectric relaxation spectroscopy (DRS) with time-domain terahertz and FTIR spectroscopy) we recently identified the mesoscopic structure in 1,3-dialkylimidazolium-based room-temperature ionic liquids (RTILs) 11 that had been 30 predicted by molecular simulations. 12,13 This structure appeared even for short-chain…”

Terahertz Time-Domain and Low-Frequency Raman Spectroscopy of Organic Materials

“…Nonetheless, once the appropriate model is known, the terahertz spectra can be used to extract unique insights into the structure and dynamics of liquids. 52 A number of groups have investigated the temperature dependence of the dielectric relaxation processes in liquid water. [59][60][61][62][63] Using THz-TDS, it was possible to determine the size of the hydration shells around dissolved protons in water.…”

Dielectric response and collective dynamics of acetonitrile

“…2). This is expected as molecular inertia, caging (dipole libration) and interaction-induced effects are dominating the terahertz region [5,[37][38][39]. As discussed in detail below, the dominating peak in the dielectric loss spectrum, ε′′(ν), at~40 GHz (1 in Fig.…”

“…Such a mode between rotational diffusion and libration was also observed in the broadband dielectric spectrum of dichloromethane [41] and seems to be a universal feature in OKE spectra [39]. However, these findings are at variance with an assignment of this contribution to the formation and breaking of dimer structures as for dichloromethane g K = 1.0 [41] and such an OKE mode is also observed for non-polar fluids [39].…”