Alexander Alijah

Quantized non-adiabatic coupling terms to ensure diabatic potentials

Abstract A way to derive rigorous diabatic potentials from non-adiabatic coupling terms (NACTs) was suggested some time ago [M. Baer, Chem. Phys. Lett. 35 (1975) 112]. This approach could be applied only for cases when the NACTs are regular throughout configuration space. In this work a criterion is established to be fulfilled by NACTs which yields continuous and uniquely diabatic potentials defined throughout configuration space. It is found that this requirement leads to a kind of `quantization with regard to the non-regular NACTs. A two-state model and a three-state model were considered as examples.

Accurate ab initio based multisheeted double many-body expansion potential energy surface for the three lowest electronic singlet states of H3+.

The authors present diabatic and adiabatic potential energy surfaces for the three lowest electronic singlet states of H3+. The modeling of the surfaces is based on the multi-sheeted double many-body expansion method which consists of dressing the various matrix elements of the diatomics-in-molecules potential matrix with three-body terms. The avoided crossing between the two lowest states and the conical intersection between the second and the third state are accurately represented by construction.

Accurate double many-body expansion potential energy surface for triplet H3+. II. The upper adiabatic sheet (2 3A′)

We report on a global potential energy hypersurface for the upper sheet of the lowest triplet state of H3+. The analytic representation is based on the double many-body expansion theory. The ab initio data points, calculated with a large cc-pV5Z basis, are represented with a root mean square deviation of only 5.54 cm(-1) in the energy region below the H(+)+2H(2S) dissociation threshold. The quasi-bound vibronic states supported by this surface have also been calculated.

Rotation–vibrational states of and the adiabatic approximation

We discuss recent progress in the calculation and identification of rotation–vibrational states of at intermediate energies up to 13u200a000u200acm−1. Our calculations are based on the potential energy surface of Cencek et al. which is of sub-microhartree accuracy. As this surface includes diagonal adiabatic and relativistic corrections to the fixed nuclei electronic energies, the remaining discrepancies between our calculated and experimental data should be due to the neglect of non-adiabatic coupling to excited electronic states in the calculations. To account for this, our calculated energy values were adjusted empirically by a simple correction formula. Based on our understanding of the adiabatic approximation, we suggest two new approaches to account for the off-diagonal adiabatic correction, which should work; however, they have not been tested yet for . Theoretical predictions made for the above-barrier energy region of recent experimental interest are accurate to 0.35u200acm−1 or better.

Hyperspherical nuclear motion of H3+ and D3+ in the electronic triplet state, aΣu+3

The potential energy surface of H(3) (+) in the lowest electronic triplet state, a (3)Sigma(u) (+), shows three equivalent minima at linear nuclear configurations. The vibrational levels of H(3) (+) and D(3) (+) on this surface can therefore be described as superimposed linear molecule states. Owing to such a superposition, each vibrational state characterized by quantum numbers of an isolated linear molecule obtains a one- and a two-dimensional component. The energy splittings between the two components have now been rationalized within a hyperspherical picture. It is shown that nuclear motion along the hyperangle phi mainly accounts for the splittings and provides upper bounds. This hyperspherical motion can be considered an extension of the antisymmetric stretching motion of the individual linear molecule.

H4(+): what do we know about it?

The potential energy surface of H(4)(+) has been analyzed and stationary points and minima of intersections characterized by benchmark multireference configuration interaction calculations with basis sets as large as augmented septuble zeta. No evidence for minima other than those of the well established stable C(2v) configuration has been found. Some of the results obtained previously at a lower level of ab initio theory had to be revised.

in the electronic triplet state: current status

We review the theoretical work carried out on the tri-hydrogen ion in the electronic triplet state 13E′, which is split into a and 23A′ by vibronic interaction. We begin with an overview on analytical potential energy surfaces and calculations of rovibrational states by focusing on our own results, which are based on the most accurate potential energy surfaces available so far. This is followed by an examination of the selection rules and predictions of infrared transition frequencies. Finally, we discuss the Slonczewski resonance states supported by the upper sheet of the potential energy surface. Theoretical work reported here may be of interest for future experiments on the title ion.

Ro-vibrational states of triplet H3+ (a3Σu+): The lowest 19 bands

Abstract We have performed extensive calculations of the ro-vibrational states of triplet H 3 + , using the method of hyperspherical harmonics and our recently reported double many-body expansion potential energy surface. The rotational term values of the lowest 19 states are presented here for a total angular momentum of J ⩽10.

Recent Progress on Small Hydrogen Molecular Ions

The hydrogen molecular ions H+n have been studied intensely by experimentalists and theoreticians. Apart from H+2 , most work has been dedicated to H+3 and mainly concerns the electronic ground state. We present some recent results on the excited electronic singlet [1] and triplet states [2, 3] before turning to the next higher member of the H+n series, H + 4 . This ion, initially characterized in the seventies and first observed in 1984, has since been largely overlooked. Indeed, recent studies focus on H+5 and H + 6 . H + 4 is interesting as the smallest of the clusters with an H+3 core. Various nuclear configurations have been suggested as stable in the literature. We have systematically explored the potential energy surface and thereby examined those structures. Benchmark calculations have been performed at the stationary points. The results of this study [4] will be presented at the conference.