Duo: a general program for calculating spectra of diatomic molecules

Duo is a general, user-friendly program for computing rotational, rovibrational and rovibronic spectra of diatomic molecules. Duo solves the Schr\"{o}dinger equation for the motion of the nuclei not only for the simple case of uncoupled, isolated electronic states (typical for the ground state of closed-shell diatomics) but also for the general case of an arbitrary number and type of couplings between electronic states (typical for open-shell diatomics and excited states). Possible couplings include spin-orbit, angular momenta, spin-rotational and spin-spin. Corrections due to non-adiabatic effects can be accounted for by introducing the relevant couplings using so-called Born-Oppenheimer breakdown curves. Duo requires user-specified potential energy curves and, if relevant, dipole moment, coupling and correction curves. From these it computes energy levels, line positions and line intensities. Several analytic forms plus interpolation and extrapolation options are available for representation of the curves. Duo can refine potential energy and coupling curves to best reproduce reference data such as experimental energy levels or line positions. Duo is provided as a Fortran 2003 program and has been tested under a variety of operating systems

Radiative cooling of H3O+ and its deuterated isotopologues

In conjunction with ab initio potential energy and dipole moment surfaces for the electronic ground state, we have made a theoretical study of the radiative lifetimes for the hydronium ion H$_3$O$^{+}$ and its deuterated isotopologues. We compute the ro-vibrational energy levels and their associated wavefunctions together with Einstein coefficients for the electric dipole transitions. A detailed analysis of the stability of the ro-vibrational states have been carried out and the longest-living states of the hydronium ions have been identified. We report estimated radiative lifetimes and cooling functions for temperatures $<$ 200 K. A number of long-living meta-stable states are identified, capable of population trapping.Comment: Phys. Chem. Chem. Phys., 201

ExoMol molecular line lists - XVI: The rotation-vibration spectrum of hot H2_2S

This work presents the AYT2 line list: a comprehensive list of 114 million $^{1}$H$_2$$^{32}$S vibration-rotation transitions computed using an empirically-adjusted potential energy surface and an {\it ab initio} dipole moment surface. The line list gives complete coverage up to 11000 \cm\ (wavelengths longer than 0.91 $\mu$m) for temperatures up to 2000 K. Room temperature spectra can be simulated up to 20000 \cm\ (0.5 $\mu$m) but the predictions at visible wavelengths are less reliable. AYT2 is made available in electronic form as supplementary data to this article and at \url{www.exomol.com}.Comment: 12 pages, 10 figures, 10 table

Low and intermediate energy electron collisions with the C2−_2^- molecular anion

Calculations are presented which use the molecular R-matrix with pseudo-states (MRMPS) method to treat electron impact electron detachment and electronic excitation of the carbon dimer anion. Resonances are found above the ionisation threshold of C$_2^-$ with $^1\Sigma^+_g$, $^1\Pi_g$ and $^3\Pi_g$ symmetry. These are shape resonances trapped by the effect of an attractive polarisation potential competing with a repulsive Coulomb interaction. The $\Pi_g$ resonances are found to give structure in the detachment cross section similar to that observed experimentally. Both excitation and detachment cross sections are found to be dominated by large impact parameter collisions whose contribution is modelled using the Born approximation.Comment: 18 pages, 5 figures constructed from 8 file

Vibrationally resolved NO dissociative excitation cross sections by electron impact

A theoretical investigation of the dissociative excitation by electron impact on the NO molecule is presented, aiming to make up for the lack of data for this process in the literature. A full set of vibrationally-resolved cross sections and corresponding rate coefficients are calculated using the Local-Complex-Potential approach and five resonant states of NO^-.Comment: 5 pages, 3 figure

Dissociative electron attachment cross sections for ro-vibrationally excited NO molecule and N- anion formation

Motivated by the huge need of data for non-equilibrium plasma modeling, a theoretical investigation of dissociative electron attachment to the NO molecule is performed. The calculations presented here are based on the Local-Complex-Potential approach, taking into account five NO$^-$ resonances. Three specific channels of the process are studied, including the production of excited nitrogen atoms $\mathrm{N}(^2\mathrm{D})$ and of its anions N$^-$. Interpretation of the existing experimental data and their comparison with our theoretical result are given. A full set of ro-vibrationally-resolved cross sections and the corresponding rate coefficients are reported. In particular, a relatively notably large cross section of N$^-$ ion formation at low energy of the incident electron and for vibrationally excited NO target is predicted. Finally, molecular rotation effects are discussed.Comment: 7 pages, 7 figure

Analysis of first overtone bands of isotopologues of CO and SiO in stellar spectra

The first overtone ($\Delta v$ = 2) bands of the monosubstituted isotopologues of CO at 2.3 $\mu$m in the spectrum of Arcturus (K2 III), and of the monosubstituted isotopologues of SiO at 4 $\mu$m in the spectrum of the red giant HD196610 (M6 III) are modelled. To investigate problems involving the computation of the first overtone bands of isotopologues of CO and SiO in spectra of late-type stars and to determine isotopic abundances. We use fits of theoretical synthetic spectra to the observed stellar molecular bands of CO and SiO to determine abundances of isotopes of C, O and Si. Fits of synthetic spectra of the \CO first overtone bands at 2.3 $\mu$m computed with three available line lists (Goorvitch, HITEMP2010 and Li et al.) to the observed spectrum of Arcturus provide the same carbon abundance [C]=$-0.6$ and isotopic ratio of carbon $^{12}$C/$^{13}$C=10 $\pm$ 2. However, the quality of fits to the observed spectrum differ for three line lists used. Furthermore, the derived oxygen isotopic ratio $^{16}$O/$^{18}$O = 2000 $\pm$ 500 is larger than that known in the solar system where $^{16}$O/$^{18}$O = 500. The silicon isotopic ratio in the atmosphere of the red giant HD196610 is revised. Using the ExoMol SiO line list with appropriate statistical weights for the SiO isotopologues the `non-solar' ratio $^{28}$Si:$^{29}$Si:$^{30}$Si = 0.86$\pm$0.03:0.12$\pm$0.02:0.02$\pm$0.01 is obtained. We found that a) the computed isotopic carbon and silicon ratios determined by the fits to the observed spectrum depend on the adopted abundance of C and Si, respectively; b) Correct treatment of the nuclear spin degeneracies parameter is of crucial importance for the use of nowadays HITRAN/ExoMol line lists in the astrophysical computations.Comment: 9 pages, 6 figures, accepted by A&