James R. Stallcop

Collision integrals and high temperature transport properties for N-N, O-O, and N-O

Accurate collision integrals for the interactions of N(4S°) + N(4S°), O(3P) + O(3P), and N(4S°) + O(3P) are reported in this paper. These are computed from a semiclassical formulation of the scattering using the best available representations of all of the potential energy curves needed to describe the collisions. Spectroscopic curves and other accurate measured data are used where available; the results of accurate ab initio electronic structure calculations are used to determine the remaining potential curves. The high-lying states are found to give the largest contributions to the collision cross sections. The nine collision integrals needed to determine transport properties to second order are tabulated for translational temperatures in the range 250-100,000 K. These results are intended to reduce the uncertainty in future predictions of the transport properties of nonequilibrium air, particularly at high temperatures. The viscosity, thermal conductivity, diffusion coefficient, and thermal diffusion factor for a gas composed of nitrogen and oxygen atoms in thermal equilibrium have been calculated. We find that the second-order contribution to the transport properties is small. Graphs of these transport properties for various mixture ratios are presented for temperatures in the range 5000-15,000 K.

Resonance charge transfer, transport cross sections, and collision integrals for N+(3P )–N(4S0) and O+(4S0)–O(3P ) interactions

N+2 and O+2 potential energy curves have been constructed by combining measured data with the results from electronic structure calculations. These potential curves have been employed to determine accurate charge exchange cross sections, transport cross sections, and collision integrals for ground state N+ –N and O+ –O interactions. The cross sections have been calculated from a semiclassical approximation to the scattering using our computer code that fits a spline curve through the discrete potential data and incorporates the proper long‐range behavior of the interaction forces. The charge exchange cross sections are slightly smaller than the values we reported previously using an asymptotic approximation and also agree well with the results of beam measurements at high energies. The collision integrals are tabulated for a broad range of temperatures 250–100 000 K and are intended to reduce the uncertainty in the values of the transport properties of nonequilibrium air, particularly at high temperatures.

Potential energy curves and transport properties for the interaction of He with other ground-state atoms

The interactions of a He atom with a heavier atom are examined for 26 different elements, which are consecutive members selected from three rows (Li–Ne, Na–Ar, and K,Ca, Ga–Kr) and column 12 (Zn, Cd) of the Periodic Table. Interaction energies are determined using high-quality ab initio calculations for the states of the molecule that would be formed from each pair of atoms in their ground states. Potential energies are tabulated for a broad range of interatomic separation distances. The results show, for example, that the energy of an alkali interaction at small separations is nearly the same as that of a rare-gas interaction with the same electron configuration for the closed shells. Furthermore, the repulsive-range parameter for this region is very short compared to its length for the repulsion dominated by the alkali-valence electron at large separations (beyond about 3–4 a0). The potential energies in the region of the van der Waals minimum agree well with the most accurate results available. The ab ...

Quantal study of the exchange reaction for N+N2 using an ab initio potential energy surface

The N+N2 exchange rate is calculated using a time-dependent quantum dynamics method on a newly determined ab initio potential energy surface (PES) for the ground 4A″ state. This ab initio PES shows a double barrier feature in the interaction region with the barrier height at 47.2 kcal/mol, and a shallow well between these two barriers, with the minimum at 43.7 kcal/mol. A quantum dynamics wave packet calculation has been carried out using the fitted PES to compute the cumulative reaction probability for the exchange reaction of N+N2(J=0). The J–K shift method is then employed to obtain the rate constant for this reaction. The calculated rate constant is compared with experimental data and a recent quasiclassical calculation using a London–Eyring–Polanyi–Sato PES. Significant differences are found between the present and quasiclassical results. The present rate calculation is the first accurate three-dimensional quantal dynamics study for the N+N2 reaction system and the ab initio PES reported here is the ...

H-N2 interaction energies, transport cross sections, and collision integrals

The energies for the interaction of a hydrogen atom with a nitrogen molecule have been calculated for large separation distances using a complete‐active‐space self‐consistent‐field/externally contracted configuration interaction method. H–N2 transport cross sections and collision integrals have been calculated using sudden approximations and a semiclassical description of the scattering. The values of these quantities are found to be close to the corresponding values determined from the average (isotropic) potential energy. The collision integrals are applied to determine diffusion and viscosity coefficients; the theoretical diffusion agrees well with the measured data available from experiments at low temperatures.

Transport properties of hydrogen

etTransport cross sections and collision integrals have been calculated for interactions of hydrogen atoms and diatomic molecules. These results were determined using accurate potential energies and quantum mechanical formulations of the scattering. Collision integrals have been tabulated for H-H and H 2 -H 2 , and have been applied to determine diffusion and viscosity. The variation of transport properties with temperature and relative composition is examined for a gas formed from H atoms and H 2 molecules. The inversion temperature is found to be about a factor 3 lower than that of earlier estimates.

The N2–N2 potential energy surface

Abstract Extensive ab initio calculations of the N 2 –N 2 interaction energy have been performed to define its anisotropic behavior with respect to molecular orientation. Additional calibration calculations with larger basis sets have been used to improve the theoretical energies at small separation distances and have been combined with experimental data for the second virial coefficient (including the results of the more recent second acoustic measurements) to determine a realistic rigid-rotor potential energy surface for the van der Waals region.

Ab initio Potential Energy Surface for H-H2

Ab initio calculations employing large basis sets are performed to determine an accurate potential energy surface for H–H2 interactions for a broad range of separation distances. At large distances, the spherically averaged potential determined from the calculated energies agrees well with the corresponding results determined from dispersion coefficients; the van der Waals well depth is predicted to be 75±3μEh. Large basis sets have also been applied to reexamine the accuracy of theoretical repulsive potential energy surfaces (25–70 kcal/mol above the H–H2 asymptote) at small interatomic separations; the Boothroyd, Keogh, Martin, and Peterson (BKMP) potential energy surface is found to agree with results of the present calculations to within the expected uncertainty (±1 kcal/mol) of the fit. Multipolar expansions of the computed H–H2 potential energy surface are reported for four internuclear separation distances (1.2, 1.401, 1.449, and 1.7a0) of the hydrogen molecule. The differential elastic scattering ...

Theoretical calculation of low-lying states of NaAr and NaXe

The potential curves X 2Σ+, A 2Π, B 2Σ+, C 2Σ+, (4) 2Σ+, (2) 2Π, and (1) 2Δ were calculated for NaAr and NaXe using a self‐consistent field plus configuration‐interaction procedure. To reduce the computational effort, the core electrons were replaced by an ab initio effective core potential. The molecular wave functions were constructed from a basis of atomic s, p, and d Gaussian‐type orbitals. Although higher angular momentum basis functions would be required to precisely determine the weak van der Waals binding at large separations, we feel that these wave functions provide an adequate description of the repulsive region of the potential curves. Our potential curves are considerably less repulsive than the semiempirical ones of Pascale and Vandeplanque and agree well with those deduced from high‐energy scattering data by Malerich and Cross. Dipole and transition moments were also computed; these moments should be a considerable improvements over those from the one‐electron semiempirical calculation of P...

HH2 collision integrals and transport coefficients

Abstract The transport cross sections and collision integrals for H H 2 interactions have been calculated from the results of accurate ab initio structure calculations using sudden scattering approximations. The low-temperature diffusion and viscosity coefficients agree well with the results of a close-coupling scattering calculation. The values calculated from the potential energies deduced from scattering measurements are in agreement with the theoretical results. The viscosity coefficients for H H and H 2 H 2 have also been calculated; the H 2 H 2 results are very close to the measured data for temperatures in the range 200–400 K.