First observation of an excited state of Li2H

Global accurate diabatic potential surfaces for the reaction H + Li2

The adiabatic potential energies for the lowest three states of a Li2H system are calculated with a high level ab initio method (MCSCF/MRCI) with a large basis set (aV5Z). The accurate three dimensional B-spline fitting method is used to map the global adiabatic potential energy surfaces, using the existing adiabatic potential energies, for the lowest two adiabatic states of the title reaction system. The different vibrational states and corresponding energies are studied for the diatomic molecule of reactant and products. In order to clearly understand the nonadiabatic process, the avoided crossing area and conical intersection are carefully studied. For further study of the nonadiabatic dynamic reaction, the diabatic potential energy surfaces are deduced in the present work.

Full-Dimensional Ab Initio Potential Energy Surface and Vibrational Energy Levels of Li2H

We built a full-dimensional analytical potential energy surface of the ground electronic state of Li₂H from ca. 20,000 ab initio multi-reference configuration interaction calculations, including core–valence correlation effects. The surface is flexible enough to accurately describe the three dissociation channels: Li (2s ²S) + LiH (¹Σ⁺), Li₂ (¹Σ_g⁺) + H (1s ²S) and 2Li (2s ²S) + H (1s ²S). Using a local fit of this surface, we calculated pure (J = 0) vibrational states of Li₂H up to the barrier to linearity (ca. 3400 cm⁻¹ above the global minimum) using a vibrational self-consistent field/virtual state configuration interaction method. We found 18 vibrational states below this barrier, with a maximum of 6 quanta in the bending mode, which indicates that Li₂H could be spectroscopically observable. Moreover, we show that some of these vibrational states are highly correlated already ca. 1000 cm⁻¹ below the height of the barrier. We hope these calculations can help the assignment of experimental spectra. In addition, the first low-lying excited states of each B₁, B₂ and A₂ symmetry of Li₂H were characterized.

On the Angular Distribution of the H+Li2 Cross Sections: a Converged Time-Independent Quantum Scattering Study

A thorough time-independent quantum scattering study is performed on a benchmark potential energy surface for the H+Li₂ reaction at the fundamental electronic state. Integral and differential cross sections are calculated along with thermal rate coefficients until convergence is reached. Our findings show that vibrational and rotational excitations of the reactant hinder reactivity, though for the latter a considerable reaction promotion was spotted as we increase the reactant rotational quantum number until the critical value of j = 4. Such a promotion then begins to retract, eventually becoming an actual inhibition for larger j. In a straightforward manner, the concept of time-independent methods implemented in this study allowed this accurate state-to-state analysis. Furthermore, a nearly isotropic behaviour of the scattering is noted to take place from the angular point of view. Remarkably, our computational protocol is ideally suited to yield converged thermal rate coefficients, revealing a non-Arrhenius pattern and showing that J-shifting approach fails to describe this particular reaction. Our results, when compared to previous and independent ones, reinforce the latest theoretical reference for future validation in the experimental field.

Quantum isotope effects on the H+Li2 reaction

This work presents a detailed study concerning the quantum isotope effects on the H+Li[Formula: see text] reaction, when the hydrogen is replaced by muonium, deuterium, and tritium. To verify such effects on these isotope reactions, it was applied an accurate time-independent quantum scattering approach to determine the dynamic properties, such as state-to-state probabilities as a function of the total energy, the product energetic distribution, and the contribution of the ro-vibrational excitation on the reaction probabilities. From the obtained results, it was possible to observe a significant increase on the promotion of the H+Li₂ reaction when hydrogen is replaced by tritium. This fact shows the importance of the isotopic substitution in the making and breaking of the chemical bonds in the reactive systems.

A detailed reactive cross section study of X + Li2 → Li + LiX, with X = H, D, T, and Mu

In this work we apply quasiclassical trajectory theory to the X + Li2 → Li + LiX reactions, with X standing for H, D, T, and Mu, in order to determine dynamical properties such as state-to-state reactive cross-section, rotational, vibrational, and translational product distributions. By using the literature benchmark potential energy surface, we were able to predict the aforementioned dynamical property in remarkable qualitative agreement with data in the literature for the H + Li2 → Li + LiH channel. Particularly, our results points toward the well known cross section independence with ro-vibrational excitations for high excitation regimes. Since the methodology is known to be well suited for the other species, as we considered the same PES, our results are expected to be similarly accurate for D, T, and Mu. The present work consists on a significant progress in this area of research, since previous theoretical calculations-based on known potential energy surface-deviated from the experimental results.

Binding energies of small lithium clusters (Lin) and hydrogenated lithium clusters (LinH)

Large coupled cluster computations utilizing the Dunning weighted correlation-consistent polarized core-valence (cc-pwCVXZ) hierarchy of basis sets have been conducted, resulting in a panoply of internally consistent geometries and atomization energies for small Li(n) and Li(n)H (n=1-4) clusters. In contrast to previous ab initio results, we predict a monotonic increase in atomization energies per atom with increasing cluster size for lithium clusters, in accordance with the historical Knudsen-effusion measurements of Wu. For hydrogenated lithium clusters, our results support previous theoretical work concerning the relatively low atomization energy per atom for Li(2)H compared to LiH and Li(3)H. The CCSD(T)/cc-pwCVQZ atomization energies for LiH, Li(2)H, Li(3)H, and the most stable isomer of Li(4)H, including zero-point energy corrections, are 55.7, 79.6, 113.0, and 130.6 kcal/mol, respectively. The latter results are not consistent with the most recent experiments of Wu.