More Like this

1. Theoretical study of the electron-induced vibrational excitation of H2O

   https://doi.org/10.1051/0004-6361/202449361  

   Ayouz, Mehdi; Faure, Alexandre; Kokoouline, Viatcheslav (July 2024, Astronomy & Astrophysics)

   This study presents calculations for cross sections of the vibrational excitation of H2O (X1A1) via electron impact. The theoretical approach employed here is based on first principles only, combining electron-scattering calculations performed using the UK R-matrix codes for several geometries of the target molecule, three-dimensional (3D) vibrational states of H2O, and 3D vibrational frame transformation. The aim is to represent the scattering matrix for the electron incident of the molecule. The vibrational wave functions were obtained numerically, without the normal-mode approximation, so that the interactions and transitions between vibrational states assigned to different normal modes could be accounted for. The thermally averaged rate coefficients were derived from the calculated cross sections for temperatures in the 10–10 000 K interval and analytical fits for rate coefficients were also provided. We assessed the uncertainty estimations of the obtained data for subsequent applications of the rate coefficients in modelling the non-local thermal equilibrium (non-LTE) spectra of water in various astrophysical environments. 

   more » « less
2. Vibrational Excitation of HDO Molecule by Electron Impact

   https://doi.org/10.3390/atoms13040032  

   Ayouz, Mehdi Adrien; Faure, Alexandre; Schneider, Ioan F; Mezei, János Zsolt; Kokoouline, Viatcheslav (April 2025, Atoms)

   Cross sections and thermally averaged rate coefficients for the vibrational excitation and de-excitation by electron impact on the HDO molecule are computed using a theoretical approach based entirely on first principles. This approach combines scattering matrices obtained from the UK R-matrix codes for various geometries of the target molecule, three-dimensional vibrational states of HDO, and the vibrational frame transformation. The vibrational states of the molecule are evaluated by solving the Schrödinger equation numerically, without relying on the normal-mode approximation, which is known to be inaccurate for water molecules. As a result, couplings and transitions between the vibrational states of HDO are accurately accounted for. From the calculated cross sections, thermally averaged rate coefficients and their analytical fits are provided. Significant differences between the results for HDO and H2O are observed. Additionally, an uncertainty assessment of the obtained data is performed for potential use in modeling non-local thermodynamic equilibrium (non-LTE) spectra of water in various astrophysical environments. 

   more » « less
3. Cross sections for vibrational excitation and dissociative recombination of the CF3+ ion in collisions with low-energy electrons

   https://doi.org/10.1088/1361-6595/ac54c0  

   Jiang, Xianwu; Liu, Hainan; Zhang, Ya; Jiang, Wei; Ayouz, Mehdi; Kokoouline, Viatcheslav (April 2022, Plasma Sources Science and Technology)

   Abstract Cross sections for the vibrational excitation and dissociative recombination (DR) of the C F 3 + ion in collisions with electrons at low scattering energies are computed using a previously-developed approach combining the normal mode approximation for the vibrational states of the target ion and the UK R -matrix code for the evaluation of the scattering matrices at fixed geometries. The obtained cross section for the DR shows excellent agreement with the experimental data from the ASTRID storage ring. Thermally-averaged rate coefficients are obtained from the cross sections for temperatures 10–3000 K. 

   more » « less
4. A wave function correction-based approach to the identification of resonances for vibrational perturbation theory

   https://doi.org/10.1063/5.0121915  

   Boyer, Mark A.; McCoy, Anne B. (October 2022, The Journal of Chemical Physics)

   An approach for identifying resonances in vibrational perturbation theory calculations is introduced. This approach makes use of the corrections to the wave functions that are obtained from non-degenerate perturbation theory calculations to identify spaces of states that must be treated with degenerate perturbation theory. Pairs of states are considered to be in resonance if the magnitude of expansion coefficients in the corrections to the wave functions in the non-degenerate perturbation theory calculation is greater than a specified threshold, χ max . This approach is applied to calculations of the vibrational spectra of CH 4 , H 2 CO, HNO 3 , and cc-HOONO. The question of how the identified resonances depend on the value of χ max and how the choice of the resonance spaces affects the calculated vibrational spectrum is further explored for H 2 CO. The approach is also compared to the Martin test [J. M. L. Martin et al., J. Chem. Phys. 103, 2589–2602 (1995)] for calculations of the vibrational spectra of H 2 CO and cc-HOONO. 

   more » « less
5. Calculation of scattering resonances in ozone using stabilization method

   Elizaveta Grushnikova, Dmitri Babikov (May 2019, 50th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting)

   Study of the formation mechanism for atmospheric ozone helps to understand development of planetary atmosphere. We focus on anomalous mass-independent isotope effect. To understand the nature of isotope effect we consider all stages of ozone formation with commonly used mechanism at the low pressure regime - energy transfer (Lindemann) mechanism which involves metastable intermediate state O3*. O3* is described by scattering resonance in quantum mechanics. Particularly, scattering resonances can be calculated using of stabilization method of Clary. Stabilization approach implies that eigenvalues change as a functions of stabilization parameter (extension of the grid boundary). Based on quantum mechanical calculations of scattering resonances, kinetic rate coefficients were computed. Found resonance states were used for calculation of kinetics rate coefficients such as equilibrium and recombination coefficients for three pressure regimes (0.3, 30 and 3000 atm). Influence of pressure was estimated as well as contributions of other kinetic parameters - stabilization constant weight of each resonance, rotational, vibrational and electronic partition functions for molecule 686 O3. 

   more » « less