Sergey A. Tashkun

Accurate spectroscopic models for methane polyads derived from a potential energy surface using high-order contact transformations.

A new spectroscopic model is developed for theoretical predictions of vibration-rotation line positions and line intensities of the methane molecule. Resonance coupling parameters of the effective polyad Hamiltionians were obtained via high-order contact transformations (CT) from ab initio potential energy surface. This allows converging vibrational and rotational levels to the accuracy of best variational calculations. Average discrepancy with centers of 100 reliably assigned experimental bands up to the triacontad range was 0.74 cm(-1) and 0.001 cm(-1) for GS rotational levels up to J = 17 in direct CT calculations without adjustable parameters. A subsequent fine tuning of the diagonal parameters allows achieving experimental accuracy for about 5600 Dyad and Pentad line positions, whereas all resonance coupling parameters were held fixed to ab initio values. Dipole transition moment parameters were determined from selected ab initio line strengths previously computed from a dipole moment surface by variational method. New polyad model allows generating a spectral line list for the Dyad and Pentad bands with the accuracy ~10(-3) cm(-1) for line positions combined with ab initio predictions for line intensities. The overall integrated intensity agreement with Hitran-2008 empirical database is of 4.4% for the Dyad and of 1.8% for the Pentad range.

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.

An isotopic-independent highly accurate potential energy surface for CO2 isotopologues and an initial 12C16O2 infrared line list

An isotopic-independent, highly accurate potential energy surface (PES) has been determined for CO(2) by refining a purely ab initio PES with selected, purely experimentally determined rovibrational energy levels. The purely ab initio PES is denoted Ames-0, while the refined PES is denoted Ames-1. Detailed tests are performed to demonstrate the spectroscopic accuracy of the Ames-1 PES. It is shown that Ames-1 yields σ(rms) (root-mean-squares error) = 0.0156 cm(-1) for 6873 J = 0-117 (12)C(16)O(2) experimental energy levels, even though less than 500 (12)C(16)O(2) energy levels were included in the refinement procedure. It is also demonstrated that, without any additional refinement, Ames-1 yields very good agreement for isotopologues. Specifically, for the (12)C(16)O(2) and (13)C(16)O(2) isotopologues, spectroscopic constants G(v) computed from Ames-1 are within ±0.01 and 0.02 cm(-1) of reliable experimentally derived values, while for the (16)O(12)C(18)O, (16)O(12)C(17)O, (16)O(13)C(18)O, (16)O(13)C(17)O, (12)C(18)O(2), (17)O(12)C(18)O, (12)C(17)O(2), (13)C(18)O(2), (13)C(17)O(2), (17)O(13)C(18)O, and (14)C(16)O(2) isotopologues, the differences are between ±0.10 and 0.15 cm(-1). To our knowledge, this is the first time a polyatomic PES has been refined using such high J values, and this has led to new challenges in the refinement procedure. An initial high quality, purely ab initio dipole moment surface (DMS) is constructed and used to generate a 296 K line list. For most bands, experimental IR intensities are well reproduced for (12)C(16)O(2) using Ames-1 and the DMS. For more than 80% of the bands, the experimental intensities are reproduced with σ(rms)(ΔI) < 20% or σ(rms)(ΔI∕δ(obs)) < 5. A few exceptions are analyzed and discussed. Directions for future improvements are discussed, though it is concluded that the current Ames-1 and the DMS should be useful in analyzing and assigning high-resolution laboratory or astronomical spectra.

New analytical model for the ozone electronic ground state potential surface and accurate ab initio vibrational predictions at high energy range.

An accurate description of the complicated shape of the potential energy surface (PES) and that of the highly excited vibration states is of crucial importance for various unsolved issues in the spectroscopy and dynamics of ozone and remains a challenge for the theory. In this work a new analytical representation is proposed for the PES of the ground electronic state of the ozone molecule in the range covering the main potential well and the transition state towards the dissociation. This model accounts for particular features specific to the ozone PES for large variations of nuclear displacements along the minimum energy path. The impact of the shape of the PES near the transition state (existence of the reef structure) on vibration energy levels was studied for the first time. The major purpose of this work was to provide accurate theoretical predictions for ozone vibrational band centres at the energy range near the dissociation threshold, which would be helpful for understanding the very complicated high-resolution spectra and its analyses currently in progress. Extended ab initio electronic structure calculations were carried out enabling the determination of the parameters of a minimum energy path PES model resulting in a new set of theoretical vibrational levels of ozone. A comparison with recent high-resolution spectroscopic data on the vibrational levels gives the root-mean-square deviations below 1 cm(-1) for ozone band centres up to 90% of the dissociation energy. New ab initio vibrational predictions represent a significant improvement with respect to all previously available calculations.

T.D.S. spectroscopic databank for spherical tops: DOS version

Abstract T.D.S. is a computer package concerned with high resolution spectroscopy of spherical top molecules like CH 4 , CF 4 , SiH 4 , SiF 4 , SnH 4 , GeH 4 , SF 6 , etc. T.D.S. contains information, fundamental spectroscopic data (energies, transition moments, spectroscopic constants) recovered from comprehensive modeling and simultaneous fitting of experimental spectra, and associated software written in C. The T.D.S. goal is to provide an access to all available information on vibration-rotation molecular states and transitions including various spectroscopic processes (Stark, Raman, etc.) under extended conditions based on extrapolations of laboratory measurements using validated theoretical models. Applications for T.D.S. may include: education/training in molecular physics, quantum chemistry, laser physics; spectroscopic applications (analysis, laser spectroscopy, atmospheric optics, optical standards, spectroscopic atlases); applications to environment studies and atmospheric physics (remote sensing); data supply for specific databases; and to photochemistry (laser excitation, multiphoton processes). The reported DOS-version is designed for IBM and compatible personal computers.

High-order contact transformations: general algorithm, computer implementation, and triatomic tests

The work is aimed at building systematic links between accurate intra-molecular potential energy surfaces (PES) and effective rovibrational Hamiltonians for polyads of near degenerate vibrational states. A specialized computing package MOL_CT of formal rovibrational calculation developed for this purpose for a semi-rigid polyatomic molecule is presented. The general algorithm of high-order calculations, computer implementation and ordering issues are discussed. The package contains a suite of routines for PES and dipole moment surfaces (DMS) analysis, coordinate and axes transformations, change of operator representations, commutator calculations and term reductions. This allows a systematic computer assisted construction of effective rovibrational Hamiltonians for successive polyads starting with a PES for nuclear motion in a give electronic state. Some applications to asymmetric-top triatomic C2v and Cs molecules with examples using recent accurate PES of water and ozone are briefly discussed.

A room temperature CO2 line list with ab initio computed intensities

Abstract Atmospheric carbon dioxide concentrations are being closely monitored by remote sensing experiments which rely on knowing line intensities with an uncertainty of 0.5% or better. We report a theoretical study providing rotation–vibration line intensities substantially within the required accuracy based on the use of a highly accurate ab initio dipole moment surface (DMS). The theoretical model developed is used to compute CO2 intensities with uncertainty estimates informed by cross comparing line lists calculated using pairs of potential energy surfaces (PES) and DMS׳s of similar high quality. This yields lines sensitivities which are utilized in reliability analysis of our results. The final outcome is compared to recent accurate measurements as well as the HITRAN2012 database. Transition frequencies are obtained from effective Hamiltonian calculations to produce a comprehensive line list covering all 12C16O2 transitions below 8000 cm − 1 and stronger than 10 − 30 cm /molecule at T = 296 K .

Description of vibration-rotation energies of nonrigid triatomic molecules using the generating function method

Abstract The generating function method previously developed is applied in this paper for fitting of the bending-rotational levels of the water molecule, where the standard power series expansion of the rotational Hamiltonian has a slow rate of convergence or even diverges. One of the possible extensions of the G -function is considered in some detail. Systematic comparisons are performed with the usual “semirigid model” of centrifugal distortion in asymmetric tops on the basis of least-squares fits to experimental energies. We adjusted the same set of sextic or octic centrifugal distortion parameters to the same experimental data. Standard deviations of fitting and (obs-calc) are typically an order of magnitude better in the generating function method. Extrapolation to higher energy levels is improved as well.

GIP: a program for experimental data reduction in molecular spectroscopy

Inverse problem which is a fit of a sample of experimental data to a multiparameter model of effective Hamiltonian H or an effective moment of transition M is an essential part of data reduction in molecular spectroscopy. In the present paper we describe a flexible inverse problem solver called GIP (General Inverse Problem) which, firstly, may be applied to a sufficiently large number of molecules, and secondly, enables one to overcome the major difficulties and limitations and provides a scientist with a useful tool to make studies in molecular spectroscopy.

A new software tool for radiative transfer calculations and its application to IMG/ADEOS data

Abstract The application of a recently created software for creative processing of IR spectra observed from space is presented in this paper. Fine Infrared Explorer for Atmospheric Radiation Measurements (FIRE-ARMS) includes forward simulation of atmospheric spectra, weighting function analysis and retrieval algorithm based on nonlinear least-squares method. The models and algorithms built in this software were applied to IR spectra with the resolution of approximately 0.1 cm −1 observed from space in the 600– 2000 cm −1 spectral region by Interferometric Monitor for Greenhouse Gases (IMG) on board of ADEOS mission during the first half of 1997. Weighting function analysis allows the user to select the optimal set of spectral intervals for fast and accurate temperature and gas profiles retrieval. Weighting function analysis allows to evaluate the necessary spectral resolutions for adequate gas profile retrieval. In this paper, temperature, H2O and CH4 profiles retrieved from IMG band 3 spectra in the range of 650– 1400 cm −1 are presented. The retrieved profiles are weakly dependent on reference profiles. The accurate retrieval of the temperature profile allows to evaluate the cloud conditions and top level of clouds. Using FIRE-ARMS software and HITRAN-96 database, 12C16O18O,13CO2 and HDO signals were identified in IMG spectra. The identification of near 1157 cm −1 feature in some IMG spectra obtained over Sahara as sand-dust aerosol signal is proposed. First, the result regarding retrieval HDO/H2O ratio using IMG spectra is presented.