Excess Internal Energy Research Articles

Surface-Assisted Laser Desorption/Ionization Mass Spectrometry with a Two-Dimensional Au Nanoparticle Array for Soft Ionization.

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) is a valuable technique for detecting small molecules in environmental and medicinal studies. We investigated dot-like and 2D-array gold nanoparticle-based SALDI-MS substrates that excite surface plasmons and enhance the desorption/ionization of sample molecules via charge transfer between the substrate and sample molecules. We aimed to optimize the nondissociative detection of sample molecules by efficiently transferring energy while suppressing excess internal energy. SALDI-MS measurements using crystal violet (CV) molecules revealed ion intensity and spectral pattern differences between the dot-like and 2D-array substrates. SALDI-MS measurements using dot-like substrates suggested two desorption/ionization processes: internal energy supply and charge transfer between the substrate and sample molecules. However, SALDI-MS measurements using 2D-array substrates suggested that the internal energy supply was suppressed. As a result, the dot-like substrate provided higher desorption/ionization efficiency but increased fragmentation, whereas the 2D-array substrate was suitable for highly sensitive and nondissociative SALDI-MS measurements. This study contributes to the optimization of SALDI-MS measurements and advances our understanding of energy transfer and sample molecule dissociation.

Viscosities of iodobenzene + n-alkane mixtures at (288.15–308.15) K. Measurements and results from models

Kinematic viscosities were measured for iodobenzene + n-alkane mixtures at (288.15–308.15) K and atmospheric pressure. The corresponding dynamic viscosities (η) were also determined using density data previously obtained in our laboratory. This set of data was employed to calculate Δη (deviations in absolute viscosity) and quantities of viscous flow. In addition, the correlation equations: McAllister, Grunberg-Nissan, Fang-He, and the Bloomfield-Dewan's model were applied to the systems: iodobenzene, or 1-chloronaphthalene, or 1,2,4-trichlorobenzene, or methyl benzoate or benzene or cyclohexane + n-alkane. It is remarkable that, within the Bloomfield-Dewan's model, residual Gibbs energies were calculated using DISQUAC with interaction parameters available in the literature. From the dependence of UVmE (isochoric molar excess internal energy) and Δη with n (the number of C atoms of the n-alkane), it is shown that the loss of fluidization of mixtures containing iodobenzene, 1,2,4-trichlorobenzene, or 1-chloronaphthalene when n increases can be ascribed to a decrease, upon mixing, of the number of broken interactions between like molecules. The breaking of correlations of molecular orientations characteristic of longer n-alkanes may explain the decreased negative Δη values of benzene mixtures with n = 14,16. The replacement, in this type of systems, of benzene by cyclohexane, leads to increased positive Δη values, probably due to the different shape of cyclohexane. On the other hand, binary mixtures formed by an aromatic polar compound mentioned above and a short n-alkane show large structural effects and large negative Δη values.From the application of the models, it seems that dispersive interactions are dominant and that size effects are not relevant on η values. The free volume model provides good results for most of the systems considered, since deviations are less than 6% for 20 mixtures from the 29 solutions under study, and only 4 systems show deviations higher than 10%, with a maximum deviation of 15%. Results improve when, within the Bloomfield-Dewan’s theory, the contribution to η of the absolute reaction rate model is also considered.

A study on the extension of correlation functions obtained from molecular dynamics simulations by the Ornstein–Zernike theory for modeled molten salts

We extend the correlation functions obtained by molecular dynamics (MD) simulation for a molten salt modeled as a superposition of the Lennard-Jones (LJ) and Coulomb potentials using the hybrid closure method, which employs the Ornstein–Zernike (OZ) theory coupled with a closure relation. An appropriate distance for switching the short-range MD part and the long-range OZ part is determined by monitoring the isothermal compressibility, excess internal energy, and pressure. The Kobryn–Gusarov–Kovalenko (KGK) closure relation is mainly employed for the hybrid closure method (MD–KGK hybrid closure). The hybrid closure with either the hypernetted chain (HNC) or Kovalenko–Hirata (KH) closure was also tested to confirm that the performance was almost equivalent to one another among the MD–HNC, MD–KH, and MD–KGK methods. The bridge function for the model molten salt is extracted using the MD–KGK hybrid closure method. At a high-density state, the bridge function shows a steep increase in the repulsive core region, as is often observed for simple fluids, whereas when the density is relatively low, the bridge function for the cation–anion pair shows a downward-sloping behavior. Furthermore, the accuracies of excess internal energy, pressure, and isothermal compressibility were also examined for the HNC, KH, and KGK approximations. For molten salt systems, these approximations exhibited a similar behavior to those for monatomic LJ fluids, especially in the high-density state. The analysis of the integrand for excess internal energy and pressure is also discussed.

On the Wavelength-Dependent Photochemistry of the Atmospheric Molecule CF3COCl.

The wavelength control of photochemistry usually results from ultrafast dynamics following the excitation of different electronic states. Here, we investigate the CF3COCl molecule, exhibiting wavelength-dependent photochemistry both via (i) depositing increasing internal energy into a single state and (ii) populating different electronic states. We reveal the mechanism behind the photon-energy dependence by combining nonadiabatic ab initio molecular dynamics techniques with the velocity map imaging experiment. We describe a consecutive mechanism of photodissociation where an immediate release of Cl taking place in an excited electronic state is followed by a slower ground-state dissociation of the CO fragment. The CO release is subject to an activation barrier and is controlled by excess internal energy via the excitation wavelength. Therefore, a selective release of CO along with Cl can be achieved. The mechanism is fully supported by both the measured kinetic energy distributions and anisotropies of the angular distributions. Interestingly, the kinetic energy of the released Cl atom is sensitively modified by accounting for spin-orbit coupling. Given the atmospheric importance of CF3COCl, we discuss the consequences of our findings for atmospheric photochemistry.

Minimum in the pressure dependence of the interfacial free energy between ice Ih and water.

Despite the importance of ice nucleation, this process has been barely explored at negative pressures. Here, we study homogeneous ice nucleation in stretched water by means of molecular dynamics seeding simulations using the TIP4P/Ice model. We observe that the critical nucleus size, interfacial free energy, free energy barrier, and nucleation rate barely change between isobars from -2600 to 500 bars when they are represented as a function of supercooling. This allows us to identify universal empirical expressions for homogeneous ice nucleation in the pressure range from -2600 to 500 bars. We show that this universal behavior arises from the pressure dependence of the interfacial free energy, which we compute by means of the mold integration technique, finding a shallow minimum around -2000 bars. Likewise, we show that the change in the interfacial free energy with pressure is proportional to the excess entropy and the slope of the melting line, exhibiting in the latter a reentrant behavior also at the same negative pressure. Finally, we estimate the excess internal energy and the excess entropy of the ice Ih-water interface.

Integral equation theory for a valence-limited model of colloidal systems

An analytic theory for the structure and thermodynamics of the Speedy-Debenedetti-Baxter valence-limited model of colloidal fluids is developed. It is based on the solution of the multidensity version of the Ornstein–Zernike equation supplemented by a Percus–Yevick-like closure relation, which are formulated for systems with a central-force type of associating potential. Our solution is reduced to the solution of a set of two algebraic equations for the fractions of free and singly bonded particles. We derive analytic expressions for the correlation functions, structure factor and excess internal energy of the model. The accuracy of the theoretical predictions is assessed through their comparison against existing and newly generated computer simulation results for the model with the valency ns=2,3,4 . Very good agreement between theoretical and computer simulation results is observed for the structural properties. Predictions for the fractions of i-times (i⩽ns) bonded particles and for excess internal energy for the model with ns=3,4 are slightly less accurate.

Integral equation theories for fluid with very short-range screened Coulomb plus power series interactions

Monte Carlo NVT simulations have been performed to obtain the thermodynamic and structural properties of fluids with a potential consisting in a hard-core and screened Coulomb plus power series (HC-SPS) interactions for three sets of the potential parameters. These ‘exact’ data are used to check the accuracy of two integral equation theories and a local excess chemical potential formula for very short-ranged potentials. The theories considered are the reference hypernetted-chain (RHNC) approximation and the local self-consistent OZ approximation (LSCOZA). The main conclusions of our study are described below. (i) The RHNC always underestimates the first peak of the radial distribution, which directly leads to an underestimation of the pressure and an overestimation of excess internal energy. In general, as the potential range becomes shorter ranged and the temperature decreases, the performance of the RHNC worsens and even becomes qualitatively incorrect. (ii) Local pressure self-consistency is of crucial importance to ensure that the hard sphere bridge function with an effective hard sphere diameter yields very accurate results for the pressure and excess internal energy even for very short-range potentials and at temperatures very close to the critical temperature. (iii) The accuracy of the excess chemical potential, obtained by thermodynamic integration of the excess internal energy, is also remarkable even for very short-ranged potentials and superior to that of a local excess chemical potential formula previously proposed [S. Zhou, Theor. Chem. Acc. 117, 555(2007)].

Mesoscopic perspectives on dynamic van der Waals theory for liquid–vapor phase transition

We present a macroscopic dynamic van der Waals theory for liquid–vapor phase transition from mesoscopic perspectives offered by the kinetic model for multiphase fluids. We show that the excess effects stem from the unbalanced long-range molecular interaction in the inhomogeneous region, and, thus, only the excess internal (potential) energy but not the excess entropy is introduced. The excess internal energy is given as −12κρ∇·∇ρ rather than the canonical 12κ∇ρ·∇ρ, which leads to the same equilibrium state but different thermohydrodynamics. The present dynamic equations are identical to the macroscopic equations recovered by the kinetic model.

Rose water in random porous media: Associative replica Ornstein-Zernike theory study

The properties of water are vastly affected by its local environment or in other words the system in which water is present. There are many systems in which water is confined in pores of different sizes and shapes. We studied the system in which porous media consisted of quenched Lennard-Jones disks and water modelled as rose water which was allowed to move inside pores. Associative replica Ornstein–Zernike theory was used to calculate the properties of the system. The accuracy of the theory under different conditions was tested against Monte Carlo simulations. The advantage of the theory is that it is magnitudes faster than computer simulations. From pair distribution functions calculated with the theory, the effects of different conditions on the structure of the system was investigated. We also studied how different conditions such as fluid temperature, fluid density, matrix density and matrix particle size affect a fraction of bonded molecules, excess internal energy and isothermal compressibility.

Analytic equation of state for the Buckingham Exp(α, m) fluids at high temperatures and densities based on the Ross variation perturbation theory

High temperatures and densities analytical thermodynamic properties are derived for the general Buckingham Exp(α, m) fluids by: a) using the Ross analytical (RA) variation perturbation theory developed by Sun [Mol. Phys. 105 (2007) 3139] for multi-Yukawa potentials; b) using a two-Yukawa potential matching the Exp(α, m), and c) introducing correcting terms which account for the discrepancies between the original Exp(α, m) potential and its two-Yukawa representation. We call this method the Ross analytical corrected theory (RAC), which leads to analytic expressions for the excess Helmholtz free energy, excess internal energy and the compressibility factor Z (i.e. the equation of state). They are valid at high temperatures and densities, since they are obtained from the Ross theory, which extends the range of validity of perturbation theories to higher densities. The matching two-Yukawa potential can also be considered as a reference potential for a first-order perturbation theory, which after further simplification leads to an analytic augmented van der Waals (avdW) theory for the above thermodynamic properties of the Exp(α, m) fluids. For the Exp(11.5, 6) and Exp(14.5, 6) fluids, the excess internal energy, compressibility factor Z and reduced pressure obtained from the RAC and avdW theories are compared with Monte Carlo (MC) simulation results corresponding to both the Exp and TY potentials. The overall accuracy of the RAC and avdW theories for the Exp(11.5, 6) fluid is also assessed in comparison to the Ross numerical (RN) theory (called also MCRSR for Mansoori, Canfield, Rasaiah, Stell and Ross) and to more complex methods such as the KLRR-T (Kang, Lee, Ree, Ree-Theostar) and the HMSA/C (hypernetted mean spherical approximation with Chebyshev approximants) theories, which require more extensive numerical calculations.

On the Nature of the Excess Internal Energy and Entropy of Metallic Glasses

The excess internal energies ΔUQ and excess entropies Delta {{S}_{Q}} of ten metallic glasses with respect to their parent crystalline states are determined from calorimetric studies. The elastic energy ΔUel of the subsystem of interstitial defects responsible for relaxation phenomena in metallic glasses according to interstitialcy theory is calculated within this theory using the measured high-frequency shear modulus. It is established that the quantities ΔUQ and ΔUel coincide with each other within an accuracy of no less than 10–15%. It is concluded that the excess internal energy and excess entropy of metallic glasses are due primarily to the elastic energy of the subsystem of interstitial defects. The dissipation of this energy into heat under heating reduces ΔUQ and ΔSQ to zero because of the complete crystallization. The entropy per defect is estimated from calorimetric data as Sd ≈ (20–30)kB, which is characteristic of interstitial defects.

Radical-Radical Reaction Dynamics Probed Using Millimeterwave Spectroscopy: Propargyl + NH2/ND2.

We apply chirped-pulse uniform flow millimeterwave (CPUF-mmW) spectroscopy to study the complex multichannel reaction dynamics in the reaction between the propargyl and amino radicals (C3H3 + NH2/ND2), a radical-radical reaction of importance in the gas-phase chemistry of astrochemical environments and combustion systems. The photolytically generated radicals are allowed to react in a well-characterized quasi-uniform supersonic flow, and mmW rotational spectroscopy (70-93 GHz) is used for simultaneous detection of the reaction products: HCN, HNC, HC3N, DCN, DNC, and DC3N, while spectral intensities of the measured pure-rotational lines allow product branching to be quantified. High-level electronic structure calculations were used for theoretical prediction of the reaction pathways and branching. Experimentally deduced product branching fractions were compared with the results from statistical simulations based on the RRKM theory. Product branching was found to be strongly dependent on the excess internal energy of the C3H3 and NH2/ND2 reactants.

Solvent Effects on Ultrafast Photochemical Pathways.

Photochemical reactions are increasingly being used for chemical and materials synthesis, for example, in photoredox catalysis, and generally involve photoexcitation of molecular chromophores dissolved in a liquid solvent. The choice of solvent influences the outcomes of the photochemistry because solute-solvent interactions modify the energies of and crossings between electronic states of the chromophores, and they affect the evolving structures of the photoexcited molecules. Ultrafast laser spectroscopy methods with femtosecond to picosecond time resolution can resolve the dynamics of these photoexcited molecules as they undergo structural and electronic changes, relax back to the ground state, dissipate their excess internal energy to the surrounding solvent, or undergo photochemical reactions. In this Account, we illustrate how experimental studies using ultrafast lasers can reveal the influences that different solvents or cosolutes exert on the photoinduced nonadiabatic dynamics of internal conversion and intersystem crossing in nonradiative relaxation pathways. Although the environment surrounding a solute molecule is rapidly changing, with fluctuations in the coordination to neighboring solvent molecules occurring on femtosecond or picosecond time scales, we show that it is possible to photoexcite selectively only those molecular chromophores transiently experiencing specific solute-solvent interactions such as intermolecular hydrogen bonding.The effects of different solvation environments on the photodynamics are illustrated using four selected examples of photochemical processes in which the solvent has a marked effect on the outcomes. We first consider two aromatic carbonyl compounds, benzophenone and acetophenone, which are known to undergo fast intersystem crossing to populate the first excited triplet state on time scales of a few picoseconds. We show that the nonadiabatic excited-state dynamics are modified by transient hydrogen bonding of the carbonyl group to a protic solvent or by coordination to a metal cation cosolute. We then examine how different solvents modify the competition between two alternative relaxation pathways in a photoexcited UVA-sunscreen molecule, diethylamino hydroxybenzoyl hexyl benzoate (DHHB). This relaxation back to the ground electronic state is an essential part of the effective operation of the sunscreen compound, but the dynamics are sensitive to the surrounding environment. Finally, we consider how solvents of different polarity affect the energies and lifetimes of excited states with locally excited or charge-transfer character in heterocyclic organic compounds used as excited-state electron donors for photoredox catalysis. With these and other examples, we seek to develop a molecular level understanding of how the choice of solution environment might be used to control the outcomes of photochemical reactions.

X-ray induced luminescence spectroscopy for DNA damaging intermediates aided by a monochromatic synchrotron radiation

Purpose To identify the bonding sites of initial radiation interaction with DNA and to trace the following chemical reaction sequences on the pathway of damage induction, we carry out a spectroscopy XIL (X-ray induced luminescence) using soft X-ray synchrotron radiation. This is a nondestructive analysis of the excited intermediate species produced in a molecular mechanism on the damage induction pathway. Materials and Methods We introduce aqueous samples of UMP (uridine-5’-monophosphate) in the vacuum by the use of a liquid micro-jet technique. The luminescence in the region of UV-VIS (from visible to ultraviolet) radiation induced after the absorption of monochromatic soft X-ray by aqueous UMP is measured with sweeping the soft X-ray energy in the region of 370–560 eV. Results The enhanced XIL intensities for aqueous UMP in the region of soft X-ray of 410–530 eV (in “water window” region) are obtained. The enhancement of XIL intensities in the UV-VIS region, relative to the water control, is explained by the excitation and ionization of a K-shell electron of nitrogen atoms in the uracil moiety. The enhanced XIL intensities do not match the structure of XANES (X-ray absorption near-edge structure) of the aqueous UMP. This suggests that the XIL intensities reflect the quantum yields of luminescence, or the quantum yields for conversion by UMP of an absorbed X-ray into UV-VIS radiation. In this paper, spectra of luminescence are shown to be resolved by combining low pass filters. The filtered luminescence spectra are obtained at the center of gravity (λc) of the band pass wavelength regions at λc = 270nm, 295 nm, 340 nm, 385 nm, 450 nm, and 525 nm., which show a trend similar to the fluorescence of nucleobases induced by ultraviolet radiation. Conclusion It is concluded that the origin of the observed XIL is the hydrated uracil moiety in aqueous UMP, decomposition of which is suppressed by the migration of excess charge and internal energy after the double ionization due to Auger decay.

Solution of the associative MSA for the patchy colloidal model with dipole-dipole interaction

An analytical solution of the associative mean spherical approximation (AMSA) for the hard-sphere multi-patch colloidal model with dipole–dipole interaction is derived. The solution is obtained using the Baxter factorization method following the scheme developed by Blum and co-workers to treat nonspherical interactions. This solution is used to build two more approximations: the exponential approximation (EXPA) and the reference AMSA. To access the accuracy of the theoretical predictions we have generated a set of exact computer simulation data for the water-like model with four tetrahedrally arranged patches and compare them against the corresponding theoretical results for the structure, excess internal energy and dielectric constant. Predictions of the reference AMSA are in a good agreement with Monte Carlo predictions. EXPA and AMSA appear to be less accurate with the accuracy of the AMSA similar to that of the regular MSA for the hard-sphere dipolar fluid. Possible extensions of the theory are briefly outlined.

Thermodynamics of mixtures containing a fluorinated benzene and a hydrocarbon

Fluorobenzene, or 1,4-difluorobenzene or hexafluorobenzene + alkane mixtures and hexafluorobenzene + benzene, or + toluene, or + 1,4-dimethylbenzene systems have been investigated using thermodynamic properties from the literature and through the application of the DISQUAC and UNIFAC (Dortmund) models and the concentration-concentration structure factor (SCC(0)) formalism. DISQUAC interaction parameters for the contacts F/alkane and F/aromatic have been determined. UNIFAC interaction parameters available in the literature for these contacts have been used along calculations. Both models predict double azeotropy for the C6F6 + C6H6 system, although in different temperature ranges. TheHmE values of the fluorobenzene, or 1,4-difluorobenzene + n-alkane systems are positive and are accurately described by the models using interaction parameters independent of the n-alkane. This means that no Patterson’s effect exists in such mixtures. DISQUAC calculations allow state that such conclusion is still valid for C6F6 + n-alkane mixtures. DISQUAC provides better results than UNIFAC on CpmE of solutions involving n-alkanes, or on HmE of C6F6 + aromatic hydrocarbon systems. Mixtures with alkanes are characterized by interactions between like molecules, which are mainly of dispersive type, which is supported, e.g, by the negative CpmE values of these systems. It is shown that structural effects can contribute largely to HmE. This is investigated in terms of the excess molar internal energy at constant volume, UVmE, whose values are determined for the investigated solutions. For mixtures with a given n-alkane, the relative variation of HmE and UVmEwith the fluorohydrocarbons is different.HmEvalues change in the sequence C6F6 > 1,4-C6H4F2 > C6H6 > C6H5F, while UVmE changes in the order: 1,4-C6H4F2 > C6H6≈ C6H5F > C6F6 . C6F6 + aromatic hydrocarbon mixtures are characterized by interactions between unlike molecules as it is demonstrated by their negative HmE values. The application of the SCC(0) formalism reveals that homocoordination is more important in C6F6 + n-alkane mixtures than in the corresponding systems with C6H5F, and that heterocoordination is dominant in the solutions of C6F6 with an aromatic hydrocarbon.

Thixotropy of soft clay: A review

Thixotropy of soil is, after softening by remoulding, a process of time-dependent return to a harder state under constant water content and constant volume conditions. This paper presents a critical review of previous investigations on the thixotropy of soft clay. Thixotropic behavior is primarily a structural effect accompanied by the spontaneous dissipation of excess internal energy, and some microstructural observations provide a deeper insight into its mechanism. Mathematical theories and models to simulate thixotropic strength recovery of soil are introduced. Different test methods to evaluate the thixotropic behavior of soil are summarized. Correlations between the thixotropic behavior of soil and some basic indexes, such as water content, Atterberg limits, mineralogy, activity and salt concentration, are described. Some remarks on future improvement for thixotropy of soil are also provided based on the results of up-to-date research.

Analytic equation of state for Mie(α, β) fluids based on an improved Ross variation perturbation theory

The analytic expressions of thermodynamic properties obtained by Sun for multi-Yukawa fluids from the Ross variation perturbation theory (Mol. Phys. 105 (2007) 3139) can be used to study other practical fluids over wide ranges of temperature and density by mimicking their intermolecular potentials with two-Yukawa (TY) functions. Using the Lennard-Jones LJ (12, 6) as an example, Sun noticed that the accuracy obtained is sensitive to the choice of the fitted TY potential. To remedy this drawback we propose in this work to introduce into Sun Ross analytical (RA) theory correction terms that take into account the discrepancies between the more general Mie(α, β) potential (the LJ is the Mie(12, 6)) and its two-Yukawa representations leading to an improved Ross analytical corrected (RAC) theory. By using three different TY potentials fitted on the LJ from the literature the corresponding excess Helmholtz free energy, excess internal energy and compressibility factor Z obtained from the Ross analytical corrected (RAC) theory are seen to be all in good agreement with the values obtained from the original Ross numerical (RN) theory applied directly to the LJ potential for a wide range of temperatures and densities. These results show that the introduction of these analytical correcting terms increases the accuracy of Sun Ross analytical (RA) theory, which also becomes less dependent on the choice of the TY parameters.

Timing angular momentum transfer for parity-unfavored transitions in multiphoton ionization

When a bound electron is photoionized from an atom or molecule, the remaining multielectron ion with excess internal energy will relax towards lower-energy states. The subsequent transverse angular momentum transfer between the parent ion and the ejected electron can lead to an electron parity-unfavored transition. Here we perform a self-calibrated timing experiment to measure the time delay of the angular momentum transfer of parity-unfavored transitions during the multiphoton ionization. We use a strong linearly polarized 400-nm light field to trigger a parity-unfavored transition in the channel of the spin-orbit excited ionic state of krypton atoms and then selectively probe the phases of the electron wave functions with different magnetic quantum numbers with a weak parallelly (orthogonally) polarized 800-nm light field. The parallel and orthogonal probes serve as the start and the stop of a stopwatch, respectively. Hence, this allows us to access the characteristic time of such an ultrafast intra-atom multielectron process.

Temperature and pressure dependence of the alpha relaxation in ortho-terphenyl.

Molecular dynamics (MD) simulations of ortho-terphenyl using an all-atom model with the optimized potentials for liquid simulations (OPLS) force field were performed both in the high temperature Arrhenian region and at lower temperatures that include the onset of the super-Arrhenian region. From the MD simulations, the internal energy of both the equilibrium liquid and crystal was determined from 300 K to 600 K and at pressures from 0.1 MPa to 1 GPa. The translational and rotational diffusivities were also determined at these temperatures and pressures for the equilibrium liquid. It is shown that within a small offset, the excess internal energy Ūx from the MD simulations is consistent with the experimentally determined excess internal energy reported earlier [Caruthers and Medvedev, Phys. Rev. Mater. 2, 055604, (2018)]. The MD mobility data {including extremely long-time 1 atm simulations from the study by Eastwood et al. [J. Phys. Chem. B 117, 12898, (2013)]} were combined with experimental data to form a unified dataset, where it was shown that in both the high temperature Arrhenian region and the lower temperature super-Arrhenian region, the mobility is a linear function of 1/Ūx(T,p), albeit with different proportionality constants. The transition between the Arrhenian and super-Arrhenian regions is relatively sharp at a critical internal energy Ūx α. The 1/Ūx(T,p) model is able to describe the mobility data over nearly 16 orders-of-magnitude. Other excess thermodynamic properties such as excess enthalpy and excess entropy (i.e., the Adam-Gibbs model) are unable to unify the pressure dependence of the mobility.