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Notes: The full interaction potential between Ne(1S) and Ne+(2P) is determined by least-squares fitting of potential parameters to spectroscopic data, principally from the near-dissociation microwave spectra of the Ne2+ complex. The potential obtained in this way incorporates the potential curves for all six electronic states correlating with Ne(1S)+Ne+(2P) and the couplings between them. Coupled-channel calculations on the potential take account of breakdown of the Born–Oppenheimer approximation and provide an accurate description of the microwave rovibronic spectrum involving levels within ∼10 cm−1 of the first dissociation limit. The Ne2+ ions are both vibrationally and rotationally hot: the spectrum involves levels up to at least J=25/2 and there is evidence for transitions involving levels near the second dissociation limit. The long-range levels involved have 〈r〉 up to 12 Å, compared with an equilibrium bond length of 1.756 Å for the ground electronic state. The long-range parameters of the interaction can be extracted from the fit and are compared with recent theoretical values. © 2002 American Institute of Physics.

Notes: We have measured and interpreted a microwave spectrum of the HeAr+ ion in which all of the observed energy levels lie within 8 cm−1 of the lowest dissociation limit, He(1S)+Ar+(2P3/2). We use an ion beam technique in which the HeAr+ ions are formed by electron impact, accelerated to kilovolt potentials, and mass-analyzed. After passage through an appropriate section of waveguide, the ions enter an electric field lens in which state-selective fragmentation occurs; the Ar+ ions produced in the lens are separated from all other ions by means of an electrostatic analyser and detected with an electron multiplier. Microwave transitions induced in the waveguide section result in population transfer which produces detected changes in the electric field-induced Ar+ fragment current. Many transitions have also been observed by a microwave–microwave double resonance technique. We have observed 68 lines spanning the frequency range 6–170 GHz; no immediately recognizable pattern is apparent. We have measured the Zeeman splitting produced by a small axial magnetic field for almost every line, which enables us to determine the values of the total angular momentum J involved in each transition, and also effective g factors for the two levels involved. We are therefore able to construct a purely experimental pattern of 37 levels lying within 8 cm−1 of the dissociation limit. The data are treated first by means of a conventional effective Hamiltonian in a case (c) basis, which allows electronic and vibrational quantum numbers to be assigned to most of the levels; the assignments are approximate, however, because very strong rotational-electronic coupling undermines the Born–Oppenheimer approximation.A more complete theoretical treatment is then presented, using the coupled-channel method in a case (e) representation to calculate the energy levels without making the Born–Oppenheimer approximation. The microwave transition frequencies and g-factors are fitted, together with earlier ultraviolet spectra, to provide a new interaction potential (designated MAL1) for He interacting with Ar+(2P3/2 and 2P1/2). The MAL1 potential is substantially more accurate than previous potentials, especially in the long-range region and for the A1 2Π3/2 state, which had not been observed before. An important new feature of the MAL1 potential is that the long-range C6 coefficient is strongly anisotropic, so that the different electronic curves have substantially different C6 coefficients. © 1995 American Institute of Physics.

Notes: We have observed a microwave spectrum of the HeKr+ ion in which all of the observed levels lie within a few cm−1 of either the first or second dissociation limit. We use an ion beam technique in which HeKr+ ions, formed by electron impact, are mass analyzed. Passage of the ion beam through an electric field lens results in selective fragmentation of energy levels lying close to dissociation. Kr+ ions formed in the lens are separated from all other ions by means of an electrostatic analyzer, and are detected with an electron multiplier. Microwave radiation induces transitions which result in population transfer and produce detected changes in the electric field-induced Kr+ fragment ion current. Additional transitions have been detected by a microwave–microwave double resonance method, and we have also made extensive use of the Zeeman effects produced by small applied coaxial magnetic fields to identify the J quantum numbers of the levels involved. Coupled channel calculations of the bound states of the He(centered ellipsis)Kr+ ion are carried out, fully including all the couplings between different electronic states correlating with He+Kr+ (2P3/2 and 2P1/2). The calculations allow the spectra to be assigned to pure rotational transitions involving levels in the X, A1, and A2 states that lie within 2.5 cm−1 of the dissociation limits. Because of a systematic near degeneracy between vibrational levels in the X and A1 states, the long-range He(centered ellipsis)Kr+ ion provides a very good example of Hund's case (e) in the form introduced by Mulliken, in which there are no projection quantum numbers onto the interatomic axis. Mulliken's case (e) is rather different from the Rydberg case (e) described by Lefebvre–Brion, and this is the first time that Mulliken's case (e) has been observed. The spectra allow the interaction potential for He(centered ellipsis)Kr+ to be determined accurately, for the first time, by least-squares fitting of potential parameters to the experimental line frequencies and g factors. The resulting interaction potential (designated MAL1) is compared with that previously determined for He(centered ellipsis)Ar+: the He(centered ellipsis)Kr+ potential is significantly shallower, because the long-range ion-induced dipole C4 coefficient is the same for the two systems but the larger Kr+ ion prevents the He atom approaching as close. © 1996 American Institute of Physics.