[en] The solution of the first principle equations of quantum mechanics provides an increasingly accurate and predictive approach for solving problems involving atoms and small molecules. A general introduction to the methods used for the ab initio calculation of rotational-vibrational spectra of small molecules is presented, with a strong focus on triatomic systems. The use of multi-reference electronic structure methods to compute molecular potential-energy and dipole-moment surfaces is discussed. Issues related to the construction of such surfaces and the inclusion of corrections due to relativistic and non-Born-Oppenheimer effects are reviewed. The derivation of exact, internal-coordinate nuclear-motion-effective Hamiltonians and their solution using a discrete-variable representation are discussed. Sample results for the water molecules are used throughout the tutorial to illustrate the theoretical and numerical issues in such calculations. (phd tutorial)

[en] The spectra (rotational, rotation–vibrational or electronic) of diatomic molecules due to transitions involving only closed-shell (¹Σ ) electronic states follow very regular, simple patterns and their theoretical analysis is usually straightforward. On the other hand, open-shell electronic states lead to more complicated spectral patterns and, moreover, often appear as a manifold of closely lying electronic states, leading to perturbed spectra of even greater complexity. This is especially true when at least one of the atoms is a transition metal. Traditionally these complex cases have been analysed using approaches based on perturbation theory, with semi-empirical parameters determined by fitting to spectral data. Recently the needs of two rather diverse scientific areas have driven the demand for improved theoretical models of open-shell diatomic systems based on an ab initio approach; these areas are ultracold chemistry and the astrophysics of ‘cool’ stars, brown dwarfs and most recently extrasolar planets. However, the complex electronic structure of these molecules combined with the accuracy requirements of high-resolution spectroscopy render such an approach particularly challenging. This review describes recent progress in developing methods for directly solving the effective Schrödinger equation for open-shell diatomic molecules, with a focus on molecules containing a transition metal. It considers four aspects of the problem: (i) the electronic structure problem; (ii) non-perturbative treatments of the curve couplings; (iii) the solution of the nuclear motion Schrödinger equation; (iv) the generation of accurate electric dipole transition intensities. Examples of applications are used to illustrate these issues. (topical review)

[en] New line lists for isotopically substituted water are presented. Most line positions were calculated from experimentally determined energy levels, while all line intensities were computed using an ab initio dipole moment surface. Transitions for which experimental energy levels are unavailable use calculated line positions. These line lists cover the range 0.05-20 000 cm^-1 and are significantly more complete and potentially more accurate than the line lists available via standard databases. All lines with intensities (scaled by isotopologue abundance) greater than 10^-29 cm/molecule at 296 K are included, augmented by weaker lines originating from pure rotational transitions. The final line lists contain 39 918 lines for H₂¹⁸O and 27 546 for H₂¹⁷O and are presented in standard HITRAN format. The number of experimentally determined H₂¹⁸O and H₂¹⁷O line positions is, respectively, 32 970 (83% of the total) and 17 073 (62%) and in both cases the average estimated uncertainty is 2×10^-4 cm^-1. The number of ab initio line intensities with an estimated uncertainty of 1% is 16 621 (42%) for H₂¹⁸O and 13 159 (48%) for H₂¹⁷O.

[en] Pure rotational lines are important for monitoring water concentrations in many environments both in space and on earth. A list of line intensities of rotational transitions for H₂¹⁶O is calculated using variational nuclear-motion wave functions and an ab initio dipole moment surface. This methodology should be equally reliable for both allowed and forbidden rotational transitions. Extensive comparisons are made with available intensity data for these transitions including the HITRAN and JPL databases. Problems are identified with some of these data. A list of 555 allowed and 846 forbidden rotational transition lines within the ground vibrational state is made available

[en] Highlights: • New, accurate empirical potential energy surface for ozone. • High accuracy dipole moment surface. • Consistent intensities computed for the three atmospheric ozone infrared bands. Monitoring ozone concentrations in the Earth’s atmosphere using spectroscopic methods is a major activity which undertaken both from the ground and from space. However there are long-running issues of consistency between measurements made at infrared (IR) and ultraviolet (UV) wavelengths. In addition, key O₃ IR bands at 10 µm, 5 µm and 3 µm also yield results which differ by a few percent when used for retrievals. These problems stem from the underlying laboratory measurements of the line intensities. Here we use quantum chemical techniques, first principles electronic structure and variational nuclear-motion calculations, to address this problem. A new high-accuracy ab initio dipole moment surface (DMS) is computed. Several spectroscopically-determined potential energy surfaces (PESs) are constructed by fitting to empirical energy levels in the region below 7000 cm${}^{-1}$ starting from an ab initio PES. Nuclear motion calculations using these new surfaces allow the unambiguous determination of the intensities of 10 µm band transitions, and the computation of the intensities of 10 µm and 5 µm bands within their experimental error. A decrease in intensities within the 3 µm is predicted which appears consistent with atmospheric retrievals. The PES and DMS form a suitable starting point both for the computation of comprehensive ozone line lists and for future calculations of electronic transition intensities.

[en] Research highlights• A novel in situ dilatometry apparatus allows the control of the applied forces on the electrochemical cell. • Processes occurring at a graphite model electrode are studied in alkylcarbonate-based electrolytes. • Measurements at different applied force emphasize gas evolution phenomena. A new equipment for in situ electrochemical dilatometry is designed and validated by studying the volumetric changes of a model electrode. The contactless measurement system permit to not influence the dilation of the sample during the tests. In addition, different forces can be applied in a selected range. Graphite is selected as model electrode and electrochemical tests in different electrolytes are carried out under different applied forces. The results of the electrodilatometric tests on graphite in EC:DMC- and in PC-based electrolyte reveal not only lithium insertion/deinsertion process, but also the presence of simultaneous phenomena like solvent evaporation, SEI formation and gas evolution. The latter has been detected by applying different forces that affect the gas uptake and release from porous separator. Controlled hydrogen evolution experiments were carried out at different applied forces in order to assess the gassing detection ability of the dilatometer. We demonstrate that with this new equipment it is possible, from thickness variation, to collect information on processes of different nature. Specifically, different applied forces emphasized gas evolution, which is a worth studying phenomenon for increasing battery safety.

[en] A new, accurate, global, mass-independent, first-principles potential energy surface (PES) is presented for the ground electronic state of the water molecule. The PES is based on 2200 energy points computed at the all-electron aug-cc-pCV6Z IC-MRCI(8,2) level of electronic structure theory and includes the relativistic one-electron mass-velocity and Darwin corrections. For H₂¹⁶O, the PES has a dissociation energy of D₀ = 41 109 cm^-1 and supports 1150 vibrational energy levels up to 41 083 cm^-1. The deviation between the computed and the experimentally measured energy levels is below 15 cm^-1 for all the states with energies less than 39 000 cm^-1. Characterization of approximate vibrational quantum numbers is performed using several techniques: energy decomposition, wave function plots, normal mode distribution, expectation values of the squares of internal coordinates, and perturbing the bending part of the PES. Vibrational normal mode labels, though often not physically meaningful, have been assigned to all the states below 26 500 cm^-1 and to many more above it, including some highly excited stretching states all the way to dissociation. Issues to do with calculating vibrational band intensities for the higher-lying states are discussed.

[en] Remote sensing experiments require high-accuracy, preferably sub-percent, line intensities and in response to this need we present computed room temperature line lists for six symmetric isotopologues of carbon dioxide: "1"3C"1"6O_2, "1"4C"1"6O_2, "1"2C"1"7O_2, "1"2C"1"8O_2, "1"3C"1"7O_2 and "1"3C"1"8O_2, covering the range 0–8000 cm"−"1. Our calculation scheme is based on variational nuclear motion calculations and on a reliability analysis of the generated line intensities. Rotation–vibration wavefunctions and energy levels are computed using the DVR3D software suite and a high quality semi-empirical potential energy surface (PES), followed by computation of intensities using an ab initio dipole moment surface (DMS). Four line lists are computed for each isotopologue to quantify sensitivity to minor distortions of the PES/DMS. Reliable lines are benchmarked against recent state-of-the-art measurements and against the HITRAN2012 database, supporting the claim that the majority of line intensities for strong bands are predicted with sub-percent accuracy. Accurate line positions are generated using an effective Hamiltonian. We recommend the use of these line lists for future remote sensing studies and their inclusion in databases. - Highlights: • Line lists presented for symmetric isotopologues of carbon dioxide. • Intensities are computed ab initio and line positions from the CDSD database. • Intensities are provided the "1"4C isotopologue.