Helium molecular model

Combining space-filling molecular models with our gas model. Figure 2.15 depicts hydrogen gas as being very similar to helium gas, except each of the particles is a hydrogen molecule. 

This chapter continues by looking at some of the macroscopic properties of simple liquids, particularly the tensile strength and flow properties. A brief discussion is then given of some molecular models of simple liquids and, finally, the unusual behaviour of liquid helium is described. 

Suppose we pump 4.0 mol of helium into a deep-sea diver s tank. If we pump in another 4.0 mol of He, the container now contains 8.0 mol of gas. The pressure can be calculated using the ideal gas equation, with n = 4.0-1-4.0 = 8.0 mol. Now suppose that we pump in 4.0 mol of molecular oxygen. Now the container holds a total of 12.0 mol of gas. According to the ideal gas model, it does not matter whether we add the same gas or a different gas. Because all molecules in a sample of an ideal gas behave independently, the pressure increases in proportion to the increase in the total number of moles of gas. Thus, we can calculate the total pressure from the ideal gas equation, using n — 8.0 + 4.0 = 12.0 mol. 

Calculations using the CDW-EIS model [38] are shown to be in good accord with 40-keV protons incident on molecular hydrogen and helium, and at this energy both theory and experiment show no evidence of any saddle-point enhancement in the doubly differential cross sections. However, for collisions involving 100-keV protons incident on molecular hydrogen and helium the CDW-EIS calculations [39] predict the existence of the saddle-point mechanism, but this is not confirmed by experiment. Recent CDW-EIS calculations and measurement for 80-keV protons on Ne by McSherry et al. [41] find no evidence of the saddle-point electron emission for this collision. 

The extent to which molecular diffusion affects dating of fractured rock has yet to be evaluated thoroughly with proper models. Although diffusion is a slow process in dense crystalline rocks, it could still have an important influence on dates of very old groundwater. With atmospherically derived radionuclides, dates of water affected by this slow diffusion should appear too old. On the other hand, dating of water based on the accumulation of helium which diffuses out of solid rock into... 

Meanwhile, computational methods have reached a level of sophistication that makes them an important complement to experimental work. These methods take into account the inhomogeneities of the bilayer, and present molecular details contrary to the continuum models like the classical solubility-diffusion model. The first solutes for which permeation through (polymeric) membranes was described using MD simulations were small molecules like methane and helium [128]. Soon after this, the passage of biologically more interesting molecules like water and protons [129,130] and sodium and chloride ions [131] over lipid membranes was considered. We will come back to this later in this section. 

Fig. 2. Atomic and molecular views of Antiprotonic Helium. The large (n, l) states in the atomic yrast region in the atomic model axe also assigned as the molecular states of corresponding rotational and vibrational quantum numbers (J,v) = (l,n — l — 1) in the one-dimensional potential for each J. The radiative transitions with Av = 0, as shown by arrows, are favoured because of the maximum overlapping of the radial densities. In this sense, the atomcule system has a dual character by itself...

Reactor effluent was continuously fed to a 0.25 ml sampling loop located inside a Hewlett-Packard Model 2520 Gas Analyzer. Separation of the products was over two serial columns, 6 x 1/8" Poropak Q 80/100 mesh, followed by 10 x 1/8" molecular sieve 5A 60/80 mesh. Thermal conductivity detection was used with helium carrier gas. Columns were isothermal at 60 C. 

Starr, T. L. and Williams, D. E. (1977a). Comparison of models for molecular hydrogen-molecular hydrogen and molecular hydrogen-helium anisotropic intermolecular repulsions. J. Chem. Phys., 66, 2054-7. [153]... 

Gas Chromatography. All gas chromatographic data were obtained on an F and M Model 810 research chromatograph. All columns were constructed of Teflon (DuPont) tubing of 4.5 mm. i.d. The carrier gas used was helium which had been passed through molecular sieves. Specific conditions for a particular experiment are given under Results. 

Thermogravimetric Analyses. All thermogravimetric analytical data were obtained on a DuPont Model 950 Thermogravimetric Analyzer. The atmosphere over the sample was helium gas which had been passed through molecular sieves. The helium flow rate was kept constant throughout all experiments at 60 ml./min., and the sample heating rate was 10°C./min. Attempts were made to keep the sample masses used as nearly the same as possible (10 mg.), to maximize comparability. 

---