A new ab initio potential energy surface for the collisional excitation of N2H(+) by H2

10 pags.; 14 figs.© 2015 AIP Publishing LLC. We compute a new potential energy surface (PES) for the study of the inelastic collisions between N2H+ and H2 molecules. A preliminary study of the reactivity of N2H+ with H2 shows that neglecting reactive channels in collisional excitation studies is certainly valid at low temperatures. The four dimensional (4D) N2H+–H2 PES is obtained from electronic structure calculations using the coupled cluster with single, double, and perturbative triple excitation level of theory. The atoms are described by the augmented correlation consistent triple zeta basis set. Both molecules were treated as rigid rotors. The potential energy surface exhibits a well depth of ≃2530 cm−1. Considering this very deep well, it appears that converged scattering calculations that take into account the rotational structure of both N2H+ and H2 should be very difficult to carry out. To overcome this difficulty, the “adiabatic-hindered-rotor” treatment, which allows para-H2(j = 0) to be treated as if it were spherical, was used in order to reduce the scattering calculations to a 2D problem. The validity of this approach is checked and we find that cross sections and rate coefficients computed from the adiabatic reduced surface are in very good agreement with the full 4D calculationsThis research was supported by the CNRS national program “Physique et Chimie du Milieu Interstellaire.” F.L. and Y.K. also thank the Agence Nationale de la Recherche (ANR-HYDRIDES), contract No. ANR-12-BS05-0011-01. We acknowledge Laurent Pagani for stimulating this work.Peer Reviewe

infection in wildfowl: a continental-scale study across Africa Understanding the ecological drivers of avian influenza virus

Despite considerable effort for surveillance of wild birds for avian influenza viruses (AIVs), empirical investigations of ecological drivers of AIV prevalence in wild birds are still scarce. Here we used a continental-scale dataset, collected in tropical wetlands of 15 African countries, to test the relative roles of a range of ecological factors on patterns of AIV prevalence in wildfowl. Seasonal and geographical variations in prevalence were positively related to the local density of the wildfowl community and to the wintering period of Eurasian migratory birds in Africa. The predominant influence of wildfowl density with no influence of climatic conditions suggests, in contrast to temperate regions, a predominant role for inter-individual transmission rather than transmission via long-lived virus persisting in the environment. Higher prevalences were found in Anas species than in non-Anas species even when we account for differences in their foraging behaviour (primarily dabbling or not) or their geographical origin (Eurasian or Afro-tropical), suggesting the existence of intrinsic differences between wildfowl taxonomic groups in receptivity to infection. Birds were found infected as often in oropharyngeal as in cloacal samples, but rarely for both types of sample concurrently, indicating that both respiratory and digestive tracts may be important for AIV replication. Keywords: influenza A virus; pathogen transmission; disease ecology; wild birds; tropical; migratio

What Should a Clinician Do When Spreading Depolarizations are Observed in a Patient?

Abstract: The International Conference on Spreading Depolarizations (iCSD) held in Boca Raton, Florida, in the September of 2018 devoted a section to address the question, “What should a clinician do when spreading depolarizations are observed in a patient?” Discussants represented a wide range of expertise, including neurologists, neurointensivists, neuroradiologists, neurosurgeons, and pre-clinical neuroscientists, to provide both clinical and basic pathophysiology perspectives. A draft summary of viewpoints offered was then written by a multidisciplinary writing group of iCSD members, based on a transcript of the session. Feedback of all discussants was formally collated, reviewed, and incorporated into the final document which was subsequently approved by all authors

BASECOL2012: A collisional database repository and web service within the Virtual Atomic and Molecular Data Centre (VAMDC)

The BASECOL2012 database is a repository of collisional data and a web service within the Virtual Atomic and Molecular Data Centre (VAMDC, http://www.vamdc.eu). It contains rate coefficients for the collisional excitation of rotational, ro-vibrational, vibrational, fine, and hyperfine levels of molecules by atoms, molecules, and electrons, as well as fine-structure excitation of some atoms that are relevant to interstellar and circumstellar astrophysical applications. Submissions of new published collisional rate coefficients sets are welcome, and they will be critically evaluated before inclusion in the database. In addition, BASECOL2012 provides spectroscopic data queried dynamically from various spectroscopic databases using the VAMDC technology. These spectroscopic data are conveniently matched to the in-house collisional excitation rate coefficients using the SPECTCOL sofware package (http:// vamdc.eu/software), and the combined sets of data can be downloaded from the BASECOL2012 website. As a partner of the VAMDC, BASECOL2012 is accessible from the general VAMDC portal (http://portal.vamdc.eu) and from user tools such as SPECTCOL

Rotational excitation of SiO by collisions with helium

Context.Within shocked regions of the interstellar medium and circumstellar environment of AGB stars the proper modelling of SiO line emission through non-LTE radiative transfer calculations requires accurate values of collisional rate coefficients. Aims.The present study focuses on the transitions among the rotational levels of the SiO molecule in its ground vibrational state induced by collision with He. The H2 molecule being the main colliding partner for the astrophysical regions of interest, the collisional process between SiO and para-H$_2(j=0)$ is also investigated in an approximated way. Methods.A new 2D SiO-He potential energy surface is computed by means of highly correlated ab initio calculations. Collisional rate coefficients corresponding to the pure rotational (de)excitation of SiO by collision with He are obtained from close-coupling quantum scattering calculations of inelastic cross sections. The SiO-He potential energy surface is also employed to compute rate coefficients for the rotational (de)excitation of SiO by collision with para-H$_2(j=0$). Results.Rate coefficients for rotational levels up to $j=26$ and kinetic temperatures in the range 10–300 K are obtained for the SiO-He colliding system. The large asymmetry of the SiO-He potential energy surface induces a propensity rule that favours odd $\Delta j$ transitions over even $\Delta j$. The estimated values of the SiO-para-H$_2(j=0$) rate coefficients are compared with those of Turner et al. (1992) for the twenty first rotational levels. As a result of significant differences between the SiO-He interaction potentials employed in the two studies, the rate coefficients are found to differ by a factor 2.5–5 for the main rotational transitions, whatever the temperature range

Inelastic rate coefficients for collisions of N2_2H+^+ with H2_2

International audienceN$_2$H$^+$ is one of the first molecular ion observed in the interstellar medium and it isfound of particular interest to probe the physical conditions of cold molecular clouds.Accurate modelling of the observed lines requires the knowledge of collisional exci-tation rate coefficients. Thus, we have calculated rate coefficients for the excitationof N$_2$H$^+$ by H$_2$, the most abundant collisional partner

Inelastic rate coefficients for collisions of C4H- with para-H2(j = 0) at low temperatures

8 pags., 9 figs., 1 tab.Anions are very reactive species that can play important roles in the chemical evolution of the interstellar medium. Following the detection of CH carbon chains, investigations on detectable anions led to the discovery of five new species during the last decade. The CH anion was first observed in the circumstellar envelope of IRC + 10216 and in TMC-1. In these cool and low-density regions, an accurate modelling of the chemical and physical conditions of the observed emission lines requires the knowledge of both radiative and collisional excitation rates. We present here the first interaction potential energy surface and inelastic rate coefficients for CH in collision with para-H(j = 0). The ab initio interaction energies were computed using highly correlated coupled cluster procedures. Quantum scattering calculations were performed with the ab initio potential energy surface. The close-coupling approach was used to compute rotational excitation cross-sections of CH for the first 21 j rotational levels (up to j = 20) and for collisional energies up to 500 cm. State-to-state rate coefficients were obtained for the temperature range 2-100 K.This work was supported by the CNRS program ‘Physique et Chimie du Milieu Interstellaire’(PCMI) co-funded by the Centre National d’Etudes Spatiales (CNES). This research was also supported by the French National Research Agency (ANR) through a grant to the Anion Cos Chem project (ANR-14-CE33-0013) and by the COST action CM1401. MLS acknowledges the MINECO for the grant ’FIS 2016-76418-P. Part of the calculations were performed using HPC resources from GENCI-[CINES/IDRIS] (grant No2010040883) and work stations at the Centre Informatique of Paris Observatory. This work was also granted access to the HPC resources of MesoPSL financed by the Region Ile de France and the project Equip@Meso (reference ANR-10-EQPX-29-01) of the programme Investissements d’Avenir supervized by the Agence Nationale pour la Recherche

Inelastic rate coefficients for collisions of C4H-with H2

International audienceCarbon-chain anions were recently detected in the interstellar medium. These very reactive species are used as tracers of the physical and chemical conditions in a variety of astrophysical environments. However, the local thermodynamic equilibrium conditions are generally not fulfilled in these environments. Therefore, collisional as well as radiative rates are needed to accurately model the observed emission lines. We determine in this work the state-to-state rate coefficients of C4H- in collision with both ortho- and para-H2. A new ab initio 4D potential energy surface was computed using explicitly correlated coupled-cluster procedures. This surface was then employed to determine rotational excitation and de-excitation cross-sections and rate coefficients for the first 21 rotational levels (up to rotational level j1 = 20) using the close-coupling method, while the coupled-state approximation was used to extend the calculations up to j1 = 30. State-to-state rate coefficients were obtained for the temperature range 2-100 K. The differences between the ortho- and para-H2 rate coefficients are found to be small. © 2021 The Author(s)

A new ab initio potential energy surface for the collisional excitation of N2_2H+^+ by H2_2

International audienceWe compute a new potential energy surface for the study of inelastic collisions between N2H+ and H2 molecules. A preliminary study of the reactivity of N2H+ with H2 shows that neglecting reactive channels in collisional excitation studies is valid at low temperatures. The four dimensional N2H+– H2 potential is obtained from electronic structure calculations using the coupled cluster with single, double and perturbative triple excitation [CCSD(T)] level of theory. The atoms are described by the augmented correlation consistent triple zeta basis set. Both molecules were treated as rigid rotors. The potential energy surface exhibits a well depth of ≃ 2530 cm−1. Considering this very deep well, it appears that converged scattering calculations that take into account both the rotational structure of the two molecules should be very difficult to carry out. To overcome this difficulty, the ”adiabatic-hindered-rotor” treatment, which allows para-H2(j = 0) to be treated as if it was spherical, was used in order to reduce the scattering calculations to a 2D problem. The validity of this approach is checked and we find that cross sections and rate coefficients computed from the adiabatic reduced surface are in very good agreement with the full 4D calculations