Emission spectrum of hot HDO in the 380-2190 cm(-1) region

Fourier transform emission spectra were recorded using a mixture of H2O and D2O at a temperature of 1500 degreesC. The spectra were recorded in three overlapping sections and cover the wavenumber range 380-2190 cm(-1). A total of 22106 lines were measured, of which 60% are thought to belong to HDO. A total of 6430 FIDO transition,, are assigned, including the first transitions to the (040) vibrational state, with a term value of 5420.042 cm(-1). A total of 1536 new energy levels of HDO belonging to the (000), (010) (020), (030), and (040) stated are presented, significantly extending the degree of rotational excitation compared to previous studies. (C) 2001 Elsevier Science

Continuous-wave cavity ringdown spectroscopy of the 8 nu polyad of water in the 25 195-25 340 cm(-1) range

State-of-the-art experiments and calculations are used to record and assign the data obtained in the weakly absorbing blue energy region of the H2O spectrum. Continuous-wave cavity ringdown absorption spectroscopy with Doppler resolution is used to probe the range from 25 195 to 25 470 cm(-1) with an absorption sensitivity of similar to 1 parts per 10(9) (ppb)/cm. 62 lines of the polyad nu(OH)=8 are reported, of which 43 are assigned using variational nuclear calculations. The study includes absorption line intensities (in the range of 10(-28)-10(-26) cm/molecule) for all lines and self-broadening pressure coefficient for a few lines. The newly obtained energy levels are also reported. (c) 2005 American Institute of Physics

Synthesis of ab initio and effective Hamiltonian line lists for ozone

A synthetic line list for the ozone molecule is presented. Variational calculation using the semi-empirical potential energy surface (PES) and ab initio dipole moment surface (DMS) produce very accurate values of line intensities, but give line positions far away from their experimental values. Furthermore assignment of approximate rotational and vibrational quantum numbers are missing from variationally calculated line list. Effective Hamiltonian calculations are complimentary to ab initio line lists in these properties giving excellent value of line positions, close to experimental ones, and a full set of quantum numbers assignment. The synthesis of both these qualities in one line list is highly desirable. Here a synthetic line list for O is presented. The method of corrections of distorted intensities in variational linelist with ab initio DMS due to the artificial intensity stealing is developed and applied. Comparison of the synthetic line list with all major published line lists and available experimental data is given. The calculated line intensities agree to within experimental error for most bands for which accurate measurements are available. 16

Calculated line lists for H216O and H218O with extensive comparisons to theoretical and experimental sources including the HITRAN2016 database

New line lists are presented for the two most abundant water isotopologues; H216O and H218O. The H216O line list extends to 25710 cm with intensity stabilities provided via ratios of calculated intensities obtained from two different semi-empirical potential energy surfaces. The line list for H218O extends to 20000 cm. The minimum intensity considered for all is cm molecule at 296 K, assuming 100% abundance for each isotopologue. Fluctuation of calculated intensities caused by changes in the underlying potential energy are found to be significant, particularly for weak transitions. Direct comparisons are made against eighteen different sources of line intensities, both experimental and theoretical, many of which are used within the HITRAN2016 database. With some exceptions, there is excellent agreement between our line lists and the experimental intensities in HITRAN2016. In the infrared region, many H216O bands which exhibit intensity differences of 5–10% between to the most recent ’POKAZATEL’ line list (Polyansky et al., [Mon. Not. Roy. Astron. Soc. 480, 2597 (2018)] and observation, are now generally predicted to within 1%. For H218O, there are systematic differences in the strongest intensities calculated in this work versus those obtained from semi-empirical calculations. In the visible, computed cross sections show smaller residuals between our work and both HITRAN2016 and HITEMP2010 than POKAZATEL. While our line list accurately reproduces HITEMP2010 cross sections in the observed region, residuals produced from this comparison do however highlight the need to update line positions in the visible spectrum of HITEMP2010. These line lists will be used to update many transition intensities and line positions in the HITRAN2016 database

Potential energy surface, dipole moment surface and the intensity calculations for the 10 µm, 5 µm and 3 µm bands of ozone

Monitoring ozone concentrations in the Earth's atmosphere using spectroscopic methods is a major activity which undertaken both from the ground and from space. However there are long-running issues of consistency between measurements made at infrared (IR) and ultraviolet (UV) wavelengths. In addition, key O 3 IR bands at 10 µm, 5 µm and 3 µm also yield results which differ by a few percent when used for retrievals. These problems stem from the underlying laboratory measurements of the line intensities. Here we use quantum chemical techniques, first principles electronic structure and variational nuclear-motion calculations, to address this problem. A new high-accuracy ab initio dipole moment surface (DMS) is computed. Several spectroscopically-determined potential energy surfaces (PESs) are constructed by fitting to empirical energy levels in the region below 7000 cm−1 starting from an ab initio PES. Nuclear motion calculations using these new surfaces allow the unambiguous determination of the intensities of 10 µm band transitions, and the computation of the intensities of 10 µm and 5 µm bands within their experimental error. A decrease in intensities within the 3 µm is predicted which appears consistent with atmospheric retrievals. The PES and DMS form a suitable starting point both for the computation of comprehensive ozone line lists and for future calculations of electronic transition intensities

Absolute ¹³C/¹²C isotope amount ratio for Vienna PeeDee Belemnite from infrared absorption spectroscopy

Measurements of isotope ratios are predominantly made with reference to standard specimens that have been characterized in the past. In the 1950s, the carbon isotope ratio was referenced to a belemnite sample collected by Heinz Lowenstam and Harold Urey in South Carolina’s PeeDee region. Due to exhaustion of the sample since then, reference materials that are traceable to the original artefact are used to define the Vienna PeeDee Belemnite scale for stable carbon isotope analysis. However, these reference materials have also become exhausted or proven to exhibit unstable composition over time, mirroring issues with the international prototype of the kilogram that led to a revised International System of Units. A campaign to elucidate the stable carbon isotope ratio of Vienna PeeDee Belemnite is underway, but independent measurement techniques are required to support it. Here we report an accurate value for the stable carbon isotope ratio inferred from infrared absorption spectroscopy, fulfilling the promise of this fundamentally accurate approach. Our results agree with a value recently derived from mass spectrometry and therefore advance the prospects of International System of Units–traceable isotope analysis. Further, our calibration-free method could improve mass balance calculations and enhance isotopic tracer studies in carbon dioxide source apportionment

An experimentally-accurate and complete room-temperature infrared HCN line-list for the HITRAN database

A hydrogen cyanide line list (MOMeNT-90) developed for the HITRAN spectroscopic database covering 0–7500 cm−1 range (λ>1330 nm) is presented. The line list is a combination of the variationally calculated line intensities with line centers obtained from experimentally derived energy levels. There are four features of this line list which distinguishes it from the previously calculated ones. First, the intensities are variationally calculated using a new, high-accuracy potential energy surface (PES) obtained via fitting the PES using experimental energy levels. Second, a new ab initio dipole moment surface was calculated at a high level of quantum chemical theory. Based on the wave functions calculated with the new PES and use of the new dipole moment surface, line intensities are reported which of similar accuracy to those obtained experimentally. Third, the calculated states are mapped to the existing complete set of experimental eigenenergies, resulting in an assigned and complete HCN line list down to the HITRAN intensity threshold of 10−34 cm/molecule. Fourth, extensive validation of the line list is provided through line-by-line comparisons of the results with measured HCN spectra which confirms the accuracy of the intensities used to construct the line list. The line list is augmented with parameters needed to calculate line widths for pressure-dependent simulations

Room temperature line lists for CO2 symmetric isotopologues with ab initio computed intensities

Remote sensing experiments require high-accuracy, preferably sub-percent, line intensities and in response to this need we present computed room temperature line lists for six symmetric isotopologues of carbon dioxide: 13C16O2, 14C16O2, 12C17O2, 12C18O2, 13C17O2 and 13C18O2, covering the range 0–8000 cm−1. Our calculation scheme is based on variational nuclear motion calculations and on a reliability analysis of the generated line intensities. Rotation–vibration wavefunctions and energy levels are computed using the DVR3D software suite and a high quality semi-empirical potential energy surface (PES), followed by computation of intensities using an ab initio dipole moment surface (DMS). Four line lists are computed for each isotopologue to quantify sensitivity to minor distortions of the PES/DMS. Reliable lines are benchmarked against recent state-of-the-art measurements and against the HITRAN2012 database, supporting the claim that the majority of line intensities for strong bands are predicted with sub-percent accuracy. Accurate line positions are generated using an effective Hamiltonian. We recommend the use of these line lists for future remote sensing studies and their inclusion in databases

Water line intensities in the near-infrared and visible

Water is the single most important molecule for models of the earth's atmosphere but line parameters for water, particularly at shorter wavelengths, are difficult to measure reliably. We suggest that the most reliable way of generating water line parameters is to combine data obtained from a variety of sources, thereby separating line parameter determination into results for strong lines, for weak lines and for isotopically substituted water. Theoretical considerations which are addressed include line assignments and labeling of energy levels and the prospects of a full theoretical solution to the water vapor problem. Particular attention is paid to strong line absorption intensities in the near-infrared where recent studies have given significantly different results. The experimental data used to construct the ESA-WVR linelist (J. Mol. Spectrosc. 208 (2001) 32) is re-analyzed with a focus on effects due to pressure determination in the cell, subtraction of the baseline and parameterization of the line profiles. A preliminary re-analysis suggests that the line intensities given by the ESA-WVR study should be closer to those of Brown et al. (J. Mol. Spectrosc. 212 (2002) 57) used in the HITRAN. This shows the vital importance of validating the data for water by independent means. (C) 2003 Elsevier Ltd. All rights reserved

ExoMol molecular line lists XIX: high-accuracy computed hot line lists for H218O and H217O

Hot line lists for two isotopologues of water, H218O and H217O, are presented. The calculations employ newly constructed potential energy surfaces (PES), which take advantage of a novel method for using the large set of experimental energy levels for H216O to give high-quality predictions for H218O and H217O. This procedure greatly extends the energy range for which a PES can be accurately determined, allowing an accurate prediction of higher lying energy levels than are currently known from direct laboratory measurements. This PES is combined with a high-accuracy, ab initio dipole moment surface of water in the computation of all energy levels, transition frequencies and associated Einstein A coefficients for states with rotational excitation up to J = 50 and energies up to 30 000 cm−1. The resulting HotWat78 line lists complement the well-used BT2 H216O line list. Full line lists are made available online as Supporting Information and at www.exomol.com