A composite ab initio energy surface is obtained for the HeH2 triatomic molecular system by combining earlier calculations that covered parts of the surface. The extended surface covers the full angular range of He relative to the H–H axis as well as the full range of He–H2 separations. As with all calculations thus far, the extended ab initio energy surface covers only a narrow range of H–H separations in the vicinity of 1.4 a.u., the equilibrium separation of ground state H2. In addition, a new parametric representation of the ab initio energy surface is developed in terms of simple analytic functions based on the physics underlying the three principal interaction mechanisms responsible for the energy surface, and collisional applications are discussed briefly. All of the interaction mechanisms give rise to three-body interaction terms, an understanding of which is crucial to interpreting the behavior of the energy surface. This parametric representation reproduces the ab initio calculated values with an average [root-mean-square (rms)] percentage error under 7%, and because the parametric form is based on the physics, it can be extrapolated into the hitherto unexplored region of large H–H separations. A very interesting double inversion of the force between the two H atoms caused by proximity of He is explained. The H–H force is repulsive for large distances of He from H2, weakly attractive for intermediate He distances, and strongly repulsive for small He distances.

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of Dj^/fj, over almost the same range of E/N for which measurements have been made for W. The ability to distinguish electrons of a current pulse in a drift-tube experiment from current due to attached electrons may enable measurements of D L /fj, to be made with greater ease than -Dy/ju in the region of E/N where electron attachment is significant. In a conventional analysis of the effect of boundary conditions imposed by the electrodes, (J.J. Lowke, Australian J. Phys. 15, 39 (1962)), the same factor 1 + cDrp/Wz^y was obtained for pressure dependent corrections in drift velocity experiments. The value of c in this case was approximately 3 to 5. A more detailed analysis of D. S. Burch predicts c to be approximately zero (private communication). 5 Tabulated values of c, and also values of #y/M, D L /fx, and W are given as a function of E/N in Westinghouse Scientific Paper No. 68-1E0-GASES-P8.Requirements are outlined for a suitable set of dynamic orbitals for theoretical studies in collision problems. The effectiof these upon the wave function, dynamic energy correction, and effective internuclear potential are all considered. It is shown that earlier forms suggested for this type of problem do not meet all required dynamic boundary conditions, principally because of their failure to recognize that physically, for moderate speed collisions, the electron at times "belongs" to the '^molecule" proper and not to either atom individually. The earlier orbitals also fail to make allowances for the reluctance of an electronic charge distribution to follow rapid rotation of an internuclear axis. These considerations suggest a new form of dynamic orbital which by remedying these deficiencies automatically achieves complete orthonormality. The results of preliminary charge transfer calculations with the new orbital basis are presented.

Approximately orthogonal channel projection operators are constructed for the charge-exchange processes in ion-atom collisions at high energies. The adiabatically perturbed stationary-state wave functions are suitably modified to take into account the motion of the heavy cores to which electrons are bound. By proper adjustment of the phase factors, it is shown that the orthogonality property between states in the modified set can be maintained. The resulting projection operators are mutually orthogonal everywhere in the configuration space, and satisfy the asymptotic requirements to first order in the electron-ion mass ratio. Single asymmetric and symmetric charge exchanges as well as double exchanges are studied in some detail, but no actual applications are given.