Gas-phase properties

Statistical mechanics computations are often tacked onto the end of ah initio vibrational frequency calculations for gas-phase properties at low pressure. For condensed-phase properties, often molecular dynamics or Monte Carlo calculations are necessary in order to obtain statistical data. The following are the principles that make this possible. 

In principle, equation-of-state procedures can be used for the calculation of hquid-phase as well as gas-phase properties, and much has been acconmlished in the development of PVT equations of state suitable for both phases. However, a widely used alternative for the hquid phase is application of excess properties. 

A cosolvent used as a miscible additive to CO2 changed the properties of the supercritical gas phase. The addition of a cosolvent resulted in increased viscosity and density of the gas mixture and enhanced extraction of the oil compounds into the C02-rich phase. Gas phase properties were measured in an equilibrium cell with a capillary viscometer and a high-pressure densitometer. Cosolvent miscibility with CO2, brine solubility, cosolvent volatility, and relative quantity of the cosolvent partitioning into the oil phase are factors that must be considered for the successful application of cosolvents. The results indicate that lower-molecular-weight additives, such as propane, are the most effective cosolvents to increase oil recovery [1472]. 

The Kohn-Sham equations have been applied to study gas-phase properties of many systems of biological interest. Most of such studies have been made for relatively small mol-... 

In Chapter 7, it was shown how the enthalpy of decomposition of an ammonium salt can be used to calculate the proton affinity of the anion. The proton affinity is a gas-phase property (as is electron affinity) that gives the intrinsic basidty of a species. The reaction of H+ with a base B can be shown as... 

The motion of polydispersed particulate phase is modeled making use of a stochastic approach. A group of representative model particles is distinguished. Motion of these particles is simulated directly taking into account the influence of the mean stream of gas and pulsations of parameters in gas phase. Properties of the gas flow — the mean kinetic energy and the rate of pulsations decay — make it possible to simulate the stochastic motion of the particles under the assumption of the Poisson flow of events. 

To see how quantum chemistry was used to predict the gas-phase properties of Y2K, see C. J. Cramer and J. T. Roberts, Science 286 (1999), 2281. To appreciate the timeliness of this publication, note the date of publication. 

Pressure-drop data obtained in these tests were correlated empirically by defining a friction-factor based on gas-phase properties and superficial gas-flow rates. This friction-factor was plotted against the group Glijll/Ggi G with the water-oil feed mass-ratio as a parameter. 

Abstract A growing tendency in chemical vapour deposition is to produce ultra-thin films or nano-objects as particles, tubes or wires. Such an objective addresses the question of a better control of the main parameters which govern the nucieation and growth steps of the deposit. This chapter focuses on the interfacial phenomena that occur at both the solid surface and the gaseous phase levels. The role of surface defects, surface reactive groups, and autocatalytic phenomena on the nucieation step are discussed by means of representative examples from the literature. In an attempt to clarify gas-phase properties, the influence of the supersaturation parameter on the nucieation step is also described. 

Other means of manipulating ions trapped in the FTMS cell include photodissociation (70-74), surface induced dissociation (75) and electron impact excitation ("EIEIO")(76) reactions. These processes can also be used to obtain structural information, such as isomeric differentiation. In some cases, the information obtained from these processes gives insight into structure beyond that obtained from collision induced dissociation reactions (74). These and other processes can be used in conjunction with FTMS to study gas phase properties of ions, such as gas phase acidities and basicities, electron affinities, bond energies, reactivities, and spectroscopic parameters. Recent reviews (4, 77) have covered many examples of the application of FTMS and ICR, in general, to these types of processes. These processes can also be used to obtain structural information, such as isomeric differentiation. 

There are no unanimous clear-cut answers. In an excellent recent review of ESI-MS of noncovalent complexes, Loo5 states that, There are three camps of opinion believers, non-believers and undecided, based on their personal experience. There are reports in the literature that demonstrate a good correlation between the solution and gas phase properties, while others report on discrepancies between the results obtained in solution and by mass spectrometry. 

For gas-phase properties, the second virial coefficient, B(T), provides one of the most sensitive tests of a water model.Both polarizable and non-polarizable models are capable of reproducing experimental values of B T), and some models have even been parameterized to do so explicitly. Polarizable models appear to provide significant improvements in reproducing not only the second virial coefficient, " but also the third coefficient. 

The effects of gas and coal/char feeds and reactor geometries upon these internal processes and, hence, upon the performance of the reactor, can be simulated with this numerical model. The model incorporates representations of particle-particle and particle-gas interactions which account for finite rate heterogeneous and homogeneous chemistry as well as the hydrodynamical processes associated with particle collisions and drag between the particles and the gas flow. The important influences of multicomponent gas phase properties as well as solid particle properties, such as shape and size, are included in the representations. 

The immersion of (HF)2 into a simulated Ar or Xe matrix led to a more linear configuration, lowering a in Fig. 3.1 from 13.6° to 8°. The proton acceptor molecule also rotated toward a less perpendicular arrangement, with p increasing from 103° to 110°. There were only very small changes observed in the internal bond lengths, although a small stretch of the interfluorine distance of the order of 0.01 A occurred. The net result is a 10% increase in the dipole moment of the (HF)2 complex. Ar matrix has little effect upon the gas-phase properties of (HC1)2, whereas immersion in Xe yields results much like those for (HF)2. 

For the present investigation the characteristic temperature difference for free convection, AT, is taken as Too—JTsI, and the gas-phase properties are evaluated at the mean temperature Tg = 1/2 (r — Tg). The thermal coeflBcient of volumetric expaimon of the gas, which appears in the Grashof number is taken as 1/Tg. Equations 30, 31, and 32 state that the gas film thickness which surrounds the droplet is infinite when the droplet is motionless relative to the gas stream and when gravity is absent. As the relative velocity increases, the film thickness becomes smaller. 

RWKl and RWK2 have been parametrized upon gas phase properties (second virial coefficient, etc) and ice properties (lattice energy and bulk moduli of three ice phases) aiming at a phase-transferable potential. 

In a very detailed study, using a combined theoretical/experimental approach. Squires et examined the gas phase properties of isomeric C3H5 anions. They were able to generate stable alkyl, 2-propenyl, 1-propenyl and cyclopropyl anions, as well as parent vinyl anions, in the gas phase by collision induced dissociation of the corresponding carboxylate anions, using the reaction sequence in Scheme 36 which was monitored by Fourier transform mass spectrometry. 

Since residual properties measure departure from ideal-gas values, their most logical use is as gas-phase properties, but in fact they also find use as hquid-phase properties. 

This problem is circumvented by a construct devised by J. W. Gibbs. Imagine that the gas-phase properties extend unchanged up to the solid surface. Differences between the actual and the unchangedproperties can then be attributed to a mathematical surface, treated as a two-dimensional phase with its own thenuodynamic properties. This provides not only a precisely defined surface phase to accountfor the singularitiesof the interfacial region, but it also extracts them from the three-dimensional gas phase so that it too may be treated precisely. The solid, despite the influence of its force field, is presumed inert and not otherwise to participate in the gas/adsorbate equilibrium. Thus for purposes of thenuodynamic analysis the adsorbate is treated as a two-dimensionalphase, inherently an open system because it is in equilibrium with the gas phase. 

Mixed-gas adsorption is treated similarly to tlie gamma/phi foniiulation of VLE (Sec. 14.1). Widi a gas-phase property denoted by superscript g, Eqs. (11.30) and (11.42), which define fugacity, are rewritten ... 

---