Low-energy cosmic rays (E less than or similar to 1 GeV) are responsible for the ionization and heating of molecular clouds. While the role of supra-thermal electrons produced in the ionization process in inducing excitation of the ambient gas (mostly molecular hydrogen) has been studied in detail, the role of primary cosmic-ray nuclei (protons and heavier nuclei) has been generally neglected. Here, we introduce, for the first time, cross sections for proton impact on H2, calculated using the semiclassical implementation of the molecular convergent close-coupling method. Our findings show that proton-induced H2 excitation is comparable in magnitude to that caused by electrons. We discuss the possible implications on the estimate of the cosmic-ray ionization rate from observations in the near-infrared domain and on the cosmic-ray-induced H2 ultraviolet luminescence. We also derive a new approximated analytical parametrization of the spectrum of secondary electrons that can be easily incorporated in numerical codes.

The predictive capabilities of population models, such as collisional-radiative and corona models, for atomic and molecular hydrogen benefit from the recent advances in the availability of reaction probabilities, particularly due to the quantum mechanical convergent close-coupling (CCC) and molecular CCC (MCCC) methods. The CCC method provides, for the first time, an extensive set of cross sections for the electron impact excitation of atomic hydrogen that are accurate at the excitation threshold, thus enabling precise model predictions at low electron temperatures. The MCCC method provides consistent sets of cross sections for electron impact (de-)excitation of molecular hydrogen with different ro-vibrational resolution, thus enabling for the first time the development of a consistent set of population models with different detail level. This consistent set of population models allows investigations with different detail level of the plasma kinetics based on the same data basis. This work guides through the (differently resolved) population models based on the Yacora solver for atomic (Yacora H) and molecular hydrogen (Yacora H 2, Yacora H 2( X1, v), Yacora H 2( v), Yacora H 2( v, N) Fulcher) applying state-of-the-art reaction probabilities and demonstrates the respective individual application possibilities.

The vibrational excitation of molecular hydrogen (H2) by low-energy electrons is one of the most fundamental reactions in atomic and molecular physics, playing a key role in the chemistry of the interstellar medium and studies of fusion plasmas. Crossed-beam experiments and electron swarm measurements have long been used to determine scattering cross sections for vibrational excitation, but the two methods produce conflicting results, a disagreement that has persisted for more than five decades and remains unsolved. Theoretical treatments have historically relied on approximations tailored to specific processes, such as separating the direct and resonant pathways or employing model polarization potentials, with no single method accurately describing all vibrational transitions. The absence of benchmark-quality calculations, combined with decades-long disagreements between experimental methods, means that even for this simple problem, there are no definitive cross-section data, leaving the reliability of theoretical approaches applied to more complex molecules uncertain and without quantified error bounds. Here we present ab initio calculations of low-energy vibrational excitation in H2 that treat electronic and vibrational motion on equal footing, providing a unified description of direct and resonant scattering across all vibrational transitions. The results are in stark contrast with previous theoretical estimates for many vibrational transitions, revealing systematic differences in both magnitude and energy dependence. At the same time, they provide strong confirmation of the swarm-derived cross sections, unlike previously accepted calculations that favored the beam data. This reversal of the long-standing situation shifts attention away from the swarm data and back onto the interpretation of the crossed-beam measurements. By providing accurate and self-consistent cross sections for vibrational excitation of H2, the present calculations will enable more reliable modeling of low-temperature plasmas and interstellar clouds.

The molecular convergent close-coupling (MCCC) method is utilized to calculate cross sections for electron scattering on the ground state of Li2. A model-potential approach is used to represent Li2 as a quasi-two-electron system above a frozen core, and configuration-interaction calculations are performed to obtain the valence states. Cross sections are calculated at incident electron energies between 0.01 and 500 eV, for elastic, excitation, ionization, and total scattering. Comparison is made with previous results where available. For the elastic-scattering cross section, qualitative agreement is found with previous calculations at low incident energies, and quantitative agreement is found at higher energies. The previously predicted 2 Pi u shape resonance is also found in the present calculations, but at a substantially lower energy and with a larger magnitude. Mixed agreement is found with previous calculations for the excitation of the 1 1 Sigma u+ and 1 3 Sigma g+ states, and for ionization. The MCCC total cross section is in reasonable agreement with the only available experiment at incident energies greater than 0.5 eV.

EDGE2D-EIRENE profiles characteristic for low recycling, high recycling and detached plasmas are postprocessed applying a vibrationally resolved collisional radiative (CR) model based on the Yacora solver to predict excited state densities and thus the molecular Lyman-, Werner- and Fulcher band emission intensities. These emission intensities are compared to predictions from the AMJUEL database standardly used in EIRENE. Lower Fulcher band and higher Lyman- and Werner band emission is predicted by the Yacora model in comparison to AMJUEL suggesting that inconsistent results from model based evaluation of measured spectra are expected depending on which model and molecular emission band is considered. The implications on detachment rate predictions are discussed.

In the theoretical study of electron-molecule collisions, resonant processes such as vibrational excitation and dissociative electron attachment and recombination are difficult to model due to the breakdown of common techniques such as the adiabatic-nuclei approximation. For this reason, it is useful to have an exactly solvable model so that the validity of different theories can be tested, such as the two-dimensional model introduced by A 97, 022704 (2018)]. We have applied the convergent close-coupling method, a well-established approach for solving a variety of scattering problems, to this two-dimensional model problem. Dissociative attachment and recombination are treated within the same formalism, and the direct and resonant contributions to vibrational excitation are both fully accounted for as a result of solving the close-coupling equations. To accurately model these processes at all energies, the two-center approach is used, in which the states of the dissociated fragments are explicitly included in the expansion of the wave function of the scattering system. Cross sections for vibrational excitation, dissociative attachment, and direct dissociation are calculated for NO-like and F2-like targets, and excellent agreement is found with existing results. Cross sections for vibrational excitation and dissociative recombination are calculated for a H2+-like target, and despite challenges with modeling the many resonances of the cross section, we find reasonably good agreement with existing results.

Cross sections for electron scattering on the ground state of LiH are calculated using the molecular convergent close-coupling method. The fixed-nuclei approximation is utilized, and calculations are performed at the mean internuclear separation of 3.06 a0 for projectile energies ranging from 0.1 to 500 eV. A model-potential approach is utilized to treat the LiH molecule as a two-electron system, and good agreement is found with the literature for various properties of the structure model. Cross sections are presented for elastic scattering, excitation to several electronic states, and ionization. Comparison is made with existing results, and qualitative agreement is found with small close-coupling calculations at low projectile energies. Good agreement is found with first-order results at high projectile energies.

A ro-vibrationally resolved corona model for the molecular hydrogen Fulcher-alpha transition based on the Yacora solver is introduced. The model couples 1365 ro-vibrational levels of the X118, d3Hu and a31 + states via electron impact excitation from the ground state into the d3Hu state and subsequent spontaneous emission into the a31+ state. For the process of electron impact excitation a set of 45260 fully ro-vibrationally resolved cross sections calculated with the molecular convergent close-coupling (MCCC) method in the adiabatic-nuclei formulation is applied. The MCCC cross sections are compared with results of a scaling method used in other works, demonstrating the need for dedicated ro-vibrationally resolved cross sections. By post-processing the model output, entire Fulcher spectra can be simulated. These spectra are benchmarked with measurements from an inductively coupled plasma discharge at a pressure between 1.1-10 Pa and a RF power of 700 W. The model results agree very well with the experiment both in relative shape and in absolute value. A non-ro-vibrationally resolved, purely electronically resolved collisional radiative model for molecular hydrogen (including further states and reaction channels) is applied to investigate the validity of the corona approximation for the benchmark plasmas and the relevance of possible process extensions of the corona model. Furthermore, the influence of collisional quenching, autoionization and predissociation is discussed.

Positron scattering from the noble gas atoms neon and argon is calculated using the single-center convergent close-coupling (CCC) method. Unlike previous CCC calculations, we have relaxed the frozen-core approximation by fully opening the outermost s and p shells, and find better agreement with experiment for excitation energies and dipole polarizability. We have used this improved structure model to calculate elastic, elastic differential, total, momentum-transfer, electron-loss, and total bound excitation cross sections. We have applied a complex model potential calculation, scaled to our single-center CCC results, to obtain direct ionization and positronium-formation cross sections for these systems. This complex model potential was also used to calculate results between the positronium-formation and ionization thresholds, giving complete results from 10- 5 eV to 5000 eV. Overall, good agreement is observed with past theory and experiment for most transitions.

Quantitative spectroscopy of molecular hydrogen has generated substantial demand, leading to the accumulation of diverse elementary process data encompassing radiative transitions, electron-impact transitions, predissociations, and quenching. However, their rates currently available are still sparse, and there are inconsistencies among those proposed by different authors. In this study, we demonstrate an experimental validation of such a molecular dataset by composing a collisional-radiative model (CRM) for molecular hydrogen and comparing experimentally obtained vibronic populations across multiple levels. From the population kinetics of molecular hydrogen, the importance of each elementary process in various parameter space is studied. In low-density plasmas (electron density n(e)less than or similar to 10(17) m(-3)) the excitation rates from the ground states and radiative decay rates, both of which have been reported previously, determine the excited state population. The inconsistency in the excitation rates affects the population distribution the most significantly in this parameter space. However, in higher density plasmas ( ne greater than or similar to 10(18) m(-3)), the excitation rates from excited states become important, which have never been reported in the literature, and may need to be approximated in some way. In order to validate these molecular datasets and approximated rates, we carried out experimental observations for two different hydrogen plasmas; a low-density radio frequency heated plasma ( n(e)approximate to 10(16) m(-3)) and the Large Helical Device (LHD) divertor plasma ( n(e)greater than or similar to 10(18) m(-3)). The visible emission lines from EF1 Sigma(+)(g), HH1 Sigma(+)(g), D-1 Pi(+/-)(u), GK(1)Sigma(+)(g), I-1 Pi(+/-)(g), J(1)Delta(+/-)(g), h(3)Sigma(+)(g), e(3)Sigma(+)(u), d(3)Pi(+/-)(u),g(3)Sigma(+)(g), i(3)Pi(+/-)(g), and j3 Delta g +/- states were observed simultaneously and their population distributions were obtained from their intensities. We compared the observed population distributions with the CRM prediction, in particular the CRM with the rates compiled by Janev et al., Miles et al., and those calculated with the molecular convergent close-coupling (MCCC) method. The MCCC prediction gives the best agreement with the experiment, particularly for the emission from the low-density plasma. However, the population distribution in the LHD divertor shows a worse agreement with the CRM than those from low-density plasma, indicating the necessity of the precise excitation rates from excited states. We also found that the rates for the electron attachment is inconsistent with experimental results. This requires further investigation.

Galactic cosmic rays (CRs) play a crucial role in ionisation, dissociation, and excitation processes within dense cloud regions where UV radiation is absorbed by dust grains and gas species. CRs regulate the abundance of ions and radicals, leading to the formation of more and more complex molecular species, and determine the charge distribution on dust grains. A quantitative analysis of these effects is essential for understanding the dynamical and chemical evolution of star-forming regions. The CR-induced photon flux has a significant impact on the evolution of the dense molecular medium in its gas and dust components. This study is intended to evaluate the flux of UV photons generated by CRs to calculate the photon-induced dissociation and ionisation rates of a vast number of atomic and molecular species, as well as the integrated UV photon flux. Our study takes advantage of recent developments in the determination of the spectra of secondary electrons, in the calculation of state-resolved excitation cross sections of H_2 by electron impact, and of photodissociation and photoionisation cross sections. We calculate the H_2 level population of each rovibrational level of the X, B, C, B', D, B”, D' and a states. We then compute the UV photon spectrum of H_2 in its line and continuum components between 72 and 700 nm, with unprecedented accuracy as a function of the CR spectrum incident on a molecular cloud, the H_2 column density, the isomeric H_2 composition, and the dust properties. The resulting photodissociation and photoionisation rates are, on average, smaller than previous determinations by a factor of about 2, with deviations up to a factor of 5. A special focus is given to the photoionisation rates of H_2, HF, and H_2, as well as to the photodissociation of H_2, which we find to be orders of magnitude higher than previous estimates.

The single-center convergent close-coupling (CCC) method is applied to calculate positron scattering from boron. A model potential approach is utilized to extract the positronium formation, direct ionization, and values between the positronium formation and ionization thresholds. We present results for total, electron loss, elastic, momentum transfer, total bound state excitation, positronium formation, direct ionization, stopping power, and mean excitation energy from 10−5 eV to 5000 eV. For boron, there is only one other set of theoretical positron calculations for elastic and momentum transfer above 500 eV, which is in excellent agreement with the current CCC results. Using the current results for boron atoms and previous CCC calculations for hydrogen and fluorine atoms, positron scattering from BF, BF2, BF3, and BH molecules is calculated for energies between 0.1 eV and 5000 eV with a modified independent atom approach.

Accurate Rayleigh and Raman scattering cross sections, tensor components, depolarization ratios, and reversal coefficients for all rovibrational transitions within the X1Σg+ ground electronic state of H2 have been calculated. Raman spectra have been generated using these data. A method for calculating Raman scattering cross sections is formulated that is valid below the ionization threshold and in the region containing resonances, which explicitly accounts for all bound and dissociative vibrational levels of the bound intermediate electronic states and approximately accounts for the ionization continuum. A representative set of cross sections is presented for incident photon energies below 15 eV and compared with existing results in the literature where possible. Convergence of our results with an increasing number of bound intermediate electronic states is demonstrated. The accuracy of the Placzek-Teller approximation is discussed. The effect of accounting for the intermediate ionization continuum is investigated. Local thermal equilibrium cross sections are calculated for Rayleigh and Raman scattering. This work represents the most accurate and complete treatment of Raman scattering for molecular hydrogen to date. A total of 9582 Rayleigh and Raman scattering cross sections have been generated and are openly available on Zenodo under an open-source Creative Commons Attribution license at https://zenodo.org/doi/10.5281/zenodo.13441471.

Single center convergent close-coupling calculations have been completed for positron scattering from atomic fluorine. Total, electron-loss, positronium-formation, direct ionization, momentum transfer, elastic, bound-state excitation, and stopping power cross sections have been determined for energies between threshold and 5000 eV. Past calculations for this scattering system exist only for elastic and momentum-transfer cross sections. For high energies, good agreement is found between current and past results. At low energies, however, large differences are found between the current calculations and previous results. The atomic fluorine results are then used in a modified independent atom approach to calculate cross sections for positron scattering on F-2, HF, CF4, C2F6, C3F6, C3F8, and C6F6. The current molecular results are typically higher than previous positron experiments across the calculated energy range, however, these experiments were not corrected for the forward angle scattering effect and likely underestimate the true result. Good agreement is found between the current positron results and previous electron experiments and calculations at high energies.

We report on the extension of the single-center convergent close-coupling method to positron scattering on multielectron atoms, along with the development of a technique for separating the direct ionization and positronium-formation channels in single-center calculations. We have performed calculations of positron scattering on carbon and present total elastic, momentum transfer, excitation, direct ionization, total ionization, total inelastic, positronium-formation, stopping power, and total cross sections from threshold to 5000 eV. We also present oscillator strengths, the scattering length, the hidden Ramsauer-Townsend minimum, the energy of the positron-carbon virtual state, and the mean excitation energy. Agreement with electron-scattering experiment and positron-scattering theory for several cross sections has been demonstrated for high energies. However, discrepancies exist between different theoretical methods at lower energies and for the ionization and positronium-formation processes.

Photoionization cross sections for all bound vibrational levels of the ground electronic state of H2+, HD+, and D2+. Vibrationally-resolved and local thermal equilibrium rate coefficients have been calculated for radiation temperatures less than 50 000 K. Fitting parameters for an analytic model of the photoionization rate coefficients have been provided. Thermally-averaged photoionization cross sections for gas temperatures of 3 000, 5 000, 8 000, 12 000, 17 000, and 23 000 K have also been included.

Photoionization cross sections for all bound vibrational levels of the 1s σ g state of H +2 are presented. The only approximation employed in our calculation of vibrationally–resolved photoionization cross sections is the Born–Oppenheimer approximation. The origin of the near threshold oscillations in the vibrationally–resolved photoionization cross sections is described. A benchmark set of photoionization cross sections are presented. Fixed–nuclei photoionization cross sections are calculated using true continuum wave functions for H +2 at an internuclear separation of 2 a 0 and compared with previous calculations with excellent agreement found in many cases, but not all.

We apply the adiabatic-nuclei molecular convergent close-coupling (MCCC) method to the study of elastic scattering and rotational excitation of H2 by 0.01-20-eV electrons. Integral cross sections are presented for all rotational transitions with |AN| 2 and Ni = 0-31 within the v = 0 vibrational level and differential cross sections for a selection of transitions. Agreement with the available measurements and previous calculations is mostly excellent, depending on the transition and incident energy. We suggest possible reasons, and argue for the accuracy of the MCCC data.

Photoionization cross sections and rate coefficients have been calculated for all bound vibrational levels of the 1s σ g state of H 2 + , HD + , and D 2 + . The Born–Oppenheimer approximation is employed in our calculation of vibrationally resolved photoionization cross sections. Vibrationally resolved and local thermal equilibrium photoionization rate coefficients are presented for photon temperatures less than 50,000 K and are found to be several orders of magnitude larger than previous results in the literature. Analytic fits for the vibrationally resolved and local thermal equilibrium photoionization rate coefficients are provided. Near-threshold oscillations in the vibrationally resolved photoionization are observed. A benchmark set of photoionization cross sections are presented. Fixed-nuclei photoionization cross sections are calculated using two-center true continuum wave functions and are verified by comparison with previous calculations and are found to be in excellent agreement in all cases. Data files for our set of benchmark cross sections, rate coefficients, and fitting parameters for H 2 + , HD + , and D 2 + are available on Zenodo under an open-source Creative Commons Attribution license at doi: 10.5281/zenodo.8304061 .