Perturbation theory for the angular correlation function

A perturbation expression for the angular pair correlation function g ⁽²⁾(r ₁₂, ω₁, ω₂) is derived for systems interacting via non central potentials based on the method developed by Gubbins and Gray [1]. The method uses the ‘correct’ (in the sense of Rushbrooke [3] and Cook and Rowlinson [4]) angle-averaged potential as the reference system about which the perturbation is made. A preliminary comparison between the original Gubbins-Gray expression for g ⁽²⁾(r ₁₂, ω₁, ω₂) and the present expression is made for a system of two-dimensional point dipoles.     

Charge and potential at the oxide/solution interface

A model of the oxide water interface postulating the existence of a finite layer of hydrolyzed material at the surface is considered. A modified Poisson-Boltzmann equation is obtained for the distribution of ions and potential in this region. Values of the titratable charge and zeta potential are calculated and found to be in good agreement with experimental values reported for these systems.     

The role of soft-core repulsions in the structure of liquids

A reformulation of the Ornstein-Zernike equation due to Baxter is used in connection with the Percus-Yevick closure for numerical solutions of the radial distribution function. It is shown that this method is useful for interaction potentials of finite range. The Lennard-Jones potential, truncated at its zero, is taken as an example, and compared with the hard sphere potential. The introduction of a finite repulsion lowers the peak of the radial distribution function appreciably, and damps its oscillations at larger distances.     

Percus-Yevick theory of adsorption

We study adsorption of hard sphere particles on to a plane surface with a delta function adsorption potential. The calculation takes account of exclusion via the Percus-Yevick approximation. At low and intermediate bulk adsorbate densities, both type II and type III BET adsorption isotherms can be found for the surface excess density and for the monolayer surface density. The surface excess isotherm agrees with an expansion of the exact surface excess isotherm to second order in the density. We mention some biochemical ramifications of the results.     

Monte Carlo simulation of hard spheroids

We present Monte Carlo simulations of the equation of state and radial distribution function for a model fluid composed of hard spheroids.     

Investigation of atmospheric {\text{O}}_{2}{\text{X}}{^{ 3}}{ \sum_{\text{g}}^{ - }} \,{\text{to}}\, {\text{b}}{^{ 1}}{ \sum_{\text{g}}^{ + }} using open-path tunable diode laser absorption spectroscopy

A tunable diode laser absorption spectroscopy (TDLAS) device fiber coupled to a pair of 12.5 in. telescopes was used to study atmospheric propagation for open path lengths of 100–1,000 meters. More than 50 rotational lines in the molecular oxygen A-band O₂ $ {\text{X}}{^{ 3}}{ \sum_{\text{g}}^{ - }} \,{\text{to}}\, {\text{b}}{^{ 1}}{ \sum_{\text{g}}^{ + }} $ transition near 760 nm were observed. Temperatures were determined from the Boltzmann rotational distribution to within 1.3 % (less than ±2 K). Oxygen concentration was obtained from the integrated spectral area of the absorption features to within 1.6 % (less than ±0.04 × 10¹⁸ molecules/cm³). Pressure was determined independently from the pressure-broadened Voigt lineshapes to within 10 %. A fourier transform interferometer (FTIR) was also used to observe the absorption spectra at 1 cm^?1 resolution. The TDLAS approach achieves a minimum observable absorbance of 0.2 %, whereas the FTIR instrument is almost 20 times less sensitive. Applications include atmospheric characterization for high energy laser propagation and validation of monocular passive raging.     

Interstitial models of water in the random mixing approximation

The interstitial models of water put forward recently by Bell and Lavis and by Perram are compared. It is shown that the two-dimensional partition function of Bell and Lavis, and the three-dimensional one of Perram, are related by a simple transformation in the important limiting case in which both models are treated according to random mixing statistics.     

Characterization of a Br(2P1/2)–CO2(1001-1000) transfer laser driven by photolysis of iodine monobromide

2 laser operating on the 10⁰1-10⁰0 transition at λ=4.3 μm and pumped by E –V energy transfer from Br(²P_1/2) has been demonstrated. The dynamics and performance of this device were characterized by observing the time-resolved stimulated emission and the steady-state spontaneous side fluorescence after photolysis of IBr or Br₂ by a frequency-doubled Nd:YAG laser or Ar⁺ laser, respectively. Although the E –V excitation kinetics are favorable, rapid vibrational relaxation limits laser action to CO₂ pressures of less than 1 Torr. Numerical modeling of laser pulse shapes and the dependence on IBr and CO₂ pressure and photolysis energy establish a relatively high gain of 0.33%/cm, a CO₂-pressure-dependent optical loss of 0.04–0.06%/cm, and an efficiency of 2×10^-5 4.3-μm-laser photons per incident photolysis photon. The CO₂ fluorescence after photolysis of a fixed Br₂/CO₂ gas mixture decreases as a function of photolysis time by about 30%/h, indicating the photolytic production of an important quencher. Received: 23 June 1997/Revised version: 23 September 1997