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.

H3+ in the electronic triplet state: current status

We review the theoretical work carried out on the tri-hydrogen ion in the electronic triplet state 1(3)E', which is split into a3Sigma+u and 2(3)A' 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 H2D+

We present rotational term values for J < or = 3 of the vibrational states with up to twofold excitation of H2D+ in the lowest electronic triplet state (a3sigma(u)+). The calculations were performed using the method of hyperspherical harmonics and our recent accurate double many-body expansion potential energy surface.

Symmetry Analysis of the Vibronic States in the Upper Conical Potential (23A‘) of Triplet

The symmetry properties of the rovibronic resonance states (Slonczewski resonances) supported by an upright conical potential are investigated. These symmetry properties lead to a useful correlation between states calculated with and without consideration of the geometrical phase, which can assist in the assignment of those states. The vibronic resonance states of triplet H3(+) (2(3)A'), which had been studied by us before, have now been assigned to spectroscopic quantum numbers.

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.

Triatomic dissociative recombination theory: Jahn–Teller coupling among infinitely many Born–Oppenheimer surfaces

The coupling of many Rydberg surfaces poses a stringent challenge for theoretical description. Yet simplifications arise because quantum defect ideas can be applied, which circumvents some of the usual difficulties that arise. We describe a theoretical technique capable of handling these complex interactions, which has already been applied with success to the dynamics of H3 Rydberg states. The extensions necessary to treat the other isotopomers H2D+ and HD2+ are then discussed, along with a preliminary application.