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The radiative association processes originating in the 1 3 Π continuum of the He ( 2 3 P ) + Li + collisional system are investigated in this study. The calculations of the dynamic collision processes are based on highly accurate state-of-the-art ab initio calculations of the potential energy functions for the 1 3 Π and the three lowest 3 Σ states of HeLi + and the associated transition dipole-moment functions. Cross-sections for the spontaneous and stimulated radiative association processes are calculated as functions of collision energy. The corresponding rate coefficients characterizing the efficiency of the formation of the molecular ion in its a 3 Σ + , b 3 Σ + , and c 3 Σ + states from the initial 1 3 Π state are obtained over a wide range of temperatures. At very low temperatures the 1 → b process has a maximum rate-coefficient value of about 7.9 × 10 − 13 cm 3 s − 1 , whereas process 1 → a reaches its maximum value of 2.0 × 10 − 13 cm 3 s − 1 at a temperature of about 500 K. Altogether the three radiative association processes investigated here can be considered as the continuum-to-bound state radiative transition part of the total quenching of the initial collision channel. [ABSTRACT FROM AUTHOR]

Depopulation of metastable He(2 1 S) by radiative association with hydrogen and lithium ions resulting in the formation of the HeH + and HeLi + molecular ions is investigated. Energy dependent cross-sections for spontaneous and stimulated processes on the spin-singlet manifold are calculated using a fully quantal approach and considering the association to rotational–vibrational states of the lowest singlet electronic states X Σ + 1 , A Σ + 1 , and B Σ + 1 from the continuum states of the B Σ + 1 electronic state. Evaluation of the cross-sections is based on highly accurate quantum calculations taking into account all possible state-to-state transitions at thermal energies (for spontaneous association) or at higher background temperatures (stimulated association). The corresponding rate coefficients are then presented as functions of temperature. As expected calculations show that the rate coefficients for radiative association to the X and A states are several orders of magnitude larger than the one for the B state formation. On the other hand, stimulation of the radiative association by black-body background radiation has a noticeable effect only on the B → B process. [ABSTRACT FROM AUTHOR]

Abstract: High level ab initio calculations are performed on the molecular ion LiHe+. Potential energy curves for the low-lying singlet and triplet electronic states are calculated using the multi-reference configuration interaction and single-reference coupled cluster methods with large basis sets. The corresponding dipole moments and transition dipole moments functions are also determined. The basic spectroscopic properties and excitation energies of the electronic states are derived from rovibrational bound state calculations. [Copyright &y& Elsevier]

Abstract: From the ab initio calculated three-dimensional adiabatic double-minimum potential energy surface of the HCO+/COH+ system and the corresponding dipole moment surface the energies of all bound vibrational states and their effective dipole moments are determined applying the Suttcliffe–Tennyson Hamiltonian for triatomic molecules. The energy and dipole data are analysed in terms of statistical methods such as the density of states approach and the nearest-neighbor level spacing distribution (NNSD). Special effort is put into investigating the effect of the tunnelling motion across the isomerization barrier on the NNSD representations. [ABSTRACT FROM AUTHOR]

Adiabatic potential energy surfaces are calculated for the ground and first excited electronic states of HeH2+ including their respective lowest dissociation limits: HeH2+(X˜ 2A′)→He(1S)+H2+(X˜ 2Σg+) and HeH2+(A˜ 2A′)→He+(2S)+H2(X˜ 1Σg+). Using the Sutcliffe–Tennyson Hamiltonian for triatomic molecules, the energies of the rotation–vibration bound states are determined variationally and the energy positions and widths of low-lying quasi-bound resonance states are obtained applying the stabilization method. For the excited electronic state a number of resonances are predicted which have considerably long lifetimes and can therefore be expected to be important for a detailed description of the chemical reactivity of the HeH2+ ion. The positions of these resonance states are shown to coincide closely with the eigenvalues of an approximate Hamiltonian derived when applying the concept of the Born–Oppenheimer adiabatic separation to the nuclear vibrational motions with different energy contents. [Copyright &y& Elsevier]