Christian Hill

The ExoMol database: Molecular line lists for exoplanet and other hot atmospheres

The ExoMol database (www.exomol.com) provides extensive line lists of molecular transitions which are valid over extended temperature ranges. The status of the current release of the database is reviewed and a new data structure is specified. This structure augments the provision of energy levels (and hence transition frequencies) and Einstein A coefficients with other key properties, including lifetimes of individual states, temperature-dependent cooling functions, Lande g-factors, partition functions, cross sections, k-coefficients and transition dipoles with phase relations. Particular attention is paid to the treatment of pressure broadening parameters. The new data structure includes a definition file which provides the necessary information for utilities accessing ExoMol through its application programming interface (API). Prospects for the inclusion of new species into the database are discussed.

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium is a worldwide consortium which federates atomic and molecular databases through an e-science infrastructure and an organisation to support this activity. About 90% of the inter-connected databases handle data that are used for the interpretation of astronomical spectra and for modelling in many fields of astrophysics. Recently the VAMDC Consortium has connected databases from the radiation damage and the plasma communities, as well as promoting the publication of data from Indian institutes. This paper describes how the VAMDC Consortium is organised for the optimal distribution of atomic and molecular data for scientific research. It is noted that the VAMDC Consortium strongly advocates that authors of research papers using data cite the original experimental and theoretical papers as well as the relevant databases.

Temperature-dependent molecular absorption cross sections for exoplanets and other atmospheres

Abstract Exoplanets, and in particular hot ones such as hot Jupiters, require very significant quantities of molecular spectroscopic data to model radiative transport in their atmospheres or to interpret their spectra. This data is commonly provided in the form of very extensive transition line lists. The size of these line lists is such that constructing a single model may require the consideration of several billion lines. We present a procedure to simplify this process based on the use of cross sections. Line lists for water, H 3 + , HCN/HNC and ammonia have been turned into cross sections on a fine enough grid to preserve their spectroscopic features. Cross sections are provided at a fixed range of temperatures and an interpolation procedure which can be used to generate cross sections at arbitrary temperatures is described. A web-based interface ( www.exomol.com/xsecs ) has been developed to allow astronomers to download cross sections at specified temperatures and spectral resolution. Specific examples are presented for water and ammonia.

ExoMol line lists – III. An improved hot rotation-vibration line list for HCN and HNC

ABSTRACT A revised rotation-vibration line list for the combined hydrogen cyanide (HCN)/ hydrogen isocyanide (HNC) system is presented. The line list uses ab initio transi-tion intensities calculated previously (Harris et al., ApJ, 2002, 578, 657) and extensivedatasets of recently measured experimental energy levels (Mellau, J. Chem. Phys. andJ. Mol. Spectrosc. 2010-2011). The resulting line list has signi cantly more accuratewavelengths than previous ones for these systems. An improved value for the sepa-ration between HCN and HNC is adopted leading to an approximately 25 % lowerpredicted thermal population of HNC as a function of temperature in the key 2000 to3000 K region. Temperature-dependent partition functions and equilibrium constantsare presented. The line lists are validated by comparison with laboratory spectra andare presented in full as supplementary data to the article and at www.exomol.com.Key words: molecular data; opacity; astronomical data bases: miscellaneous; planetsand satellites: atmospheres; stars: low-mass

ExoMol molecular line lists – XIII. The spectrum of CaO

An accurate line list for calcium oxide is presented covering transitions between all bound ro-vibronic levels from the five lowest electronic states X 1Σ+, A′ 1Π, A 1Σ+, a 3Π, and b 3Σ+. The ro-vibronic energies and corresponding wavefunctions were obtained by solving the fully coupled Schrodinger equation. Ab initio potential energy, spin-orbit, and electronic angular momentum curves were refined by fitting to the experimental frequencies and experimentally derived energies available in the literature. Using our refined model we could (1) reassign the vibronic states for a large portion of the experimentally derived energies (van Groenendael A., Tudorie M., Focsa C., Pinchemel B., Bernath P. F., 2005, J. Mol. Spectrosc., 234, 255), (2) extended this list of energies to J = 61–118 and (3) suggest a new description of the resonances from the A 1Σ+−X 1Σ+ system. We used high level ab initio electric dipole moments reported previously (Khalil H., Brites V., Le Quere F., Leonard C., 2011, Chem. Phys., 386, 50) to compute the Einstein A coefficients. Our work is the first fully coupled description of this system. Our line list is the most complete catalogue of spectroscopic transitions available for 40Ca16O and is applicable for temperatures up to at least 5000 K. CaO has yet to be observed astronomically but its transitions are characterized by being particularly strong which should facilitate its detection. The CaO line list is made available in an electronic form as supplementary data to this article and at www.exomol.com

Study of the electronic and rovibronic structure of the X 2Σ+, A 2Π, and B 2Σ+ states of AlO

The electronic structure of the X (2)Σ(+), A (2)Π, and B (2)Σ(+) states of aluminum monoxide (AlO) are studied via ab initio multi-reference configuration interaction calculations. Core correlation corrections, several basis sets, and active space choices are considered. Angular momentum and spin-orbit coupling terms are obtained at different levels of theory. The resulting ab initio curves are used to solve the associated rovibronic problem for the total angular momentum J up to 112.5 and then also refined by fitting to the experimental wavenumbers available in the literature, reproducing them with the root-mean-square error of 0.07 cm(-1). Theoretical rovibronic energy levels of AlO in its X (2)Σ(+), A (2)Π, and B (2)Σ(+) electronic states are presented including those from the X - B blue-green system.

Absorption of solar radiation by water vapor in clear and cloudy skies: Implications for anomalous absorption

We present ground-based measurements of integrated atmospheric absorption obtained using a zenith-pointing spectrometer for the wavelength region 550-1000 nm. A nonlinear, least squares fitting routine is used to fit the structured and unstructured components of the spectra, including the water vapor bands at 720, 820, and 940 nm. The structured component is found to be well-accounted for by line-by-line calculations based on known absorptions of molecular H 2 O and O 2 . No other significant structured features are observed, apart from those due to Fraunhofer lines. A recently published theoretical cross section for H 2 O dimer is also assessed in this wavelength region. Lower limit calculations of the dimer abundance based on the fitted monomer amounts suggest that this cross section is incorrect and would overestimate the potential absorption due to the dimer. Overall, the structured absorption of solar radiation under both clear- and cloudy-sky conditions is found to be well reproduced by known absorption mechanisms.

VAMDC--The Virtual Atomic and Molecular Data Centre--A New Way to Disseminate Atomic and Molecular Data--VAMDC Level 1 Release

The Virtual Atomic and Molecular Data Centre (VAMDC, http://www.vamdc.eu/) is a European‐Union‐funded collaboration between groups involved in the generation, evaluation, and use of atomic and molecular data. VAMDC aims to build a reliable, open, flexible and interoperable e‐science interface to existing atomic and molecular data. The project will cover establishing the core consortium, the development and deployment of the infrastructure and the development of interfaces to the existing atomic and molecular databases. This paper describes the organisation of the project and the achievements during its first year.

A broadband lidar for the measurement of tropospheric constituent profiles from the ground

In this paper we describe a novel lidar that combines differential UV-visible absorption spectroscopy and the lidar technique. The critical and novel element of the system is the use of an imaging spectrometer in conjunction with a two-dimensional CCD detector array to simultaneously spectrally and temporally resolve backscattered radiation. To exploit this approach, the lidar system utilizes a broadband laser output of 10–20 nm full width at half maximum tunable across the UV-visible spectral region, thus allowing the simultaneous measurement of multiple molecular species by the differential optical absorption spectroscopy technique. To demonstrate the flexibility of the technique for tropospheric composition monitoring we present initial results for both elastic and inelastic (Raman) backscatter and for absorption studies in the spectral regions where NO3 and H2O absorb. In addition, the technique has applicability for a wide range of molecules including O3, NO2, and other spectrally structured absorbers and for atmospheric temperature sounding, which may be derived from either rotational Raman return or temperature dependent absorptions such as those of O2.

Pressure-shift measurements of the oxygen A -band by Fourier-transform spectroscopy

Abstract The pressure shifts, δ , of the (0–0) band of the b 1 Σ g + –X 3 Σ g − electronic transition of oxygen (the so-called ‘ A -band’) have been measured at room temperature using high-resolution Fourier transform spectroscopy. The rotational dependence of δ has been measured and characterised; the average value of the shift over the whole band is −0.009±0.001 cm −1 atm −1 . No significant variation in δ is found for different O 2 mixing ratios in N 2 , and the results presented here are therefore appropriate for high-resolution atmospheric applications using the O 2 A -band.