Search

The results of an IUPAC Task Group formed in 2004 on “A Database of Water Transitions from Experiment and Theory” (Project No. 2004-035-1-100) are presented. Energy levels and recommended labels involving exact and approximate quantum numbers for the main isotopologues of water in the gas phase, H216O, H218O, H217O, HD16O, HD18O, HD17O, D216O, D218O, and D217O, are determined from measured transition wavenumbers. The transition wavenumbers and energy levels are validated using the MARVEL (measured active rotational–vibrational energy levels) approach and first-principles nuclear motion computations. The extensive data, e.g., more than 200,000 transitions have been handled for H216O, including lines and levels that are required for analysis and synthesis of spectra, thermochemical applications, the construction of theoretical models, and the removal of spectral contamination by ubiquitous water lines. These datasets can also be used to assess where measurements are lacking for each isotopologue and to provide accurate frequencies for many yet-to-be measured transitions. The lack of high-quality frequency calibration standards in the near infrared is identified as an issue that has hindered the determination of high-accuracy energy levels at higher frequencies. The generation of spectra using the MARVEL energy levels combined with transition intensities computed using high accuracy ab initio dipole moment surfaces are discussed.

In semi-classical line-shape calculations, the internal motions of the colliding pair are treated via quantum mechanics and the collision trajectory is determined by classical dynamics. The quantum mechanical component, i.e. the determination of reduced matrix elements (RME) for the colliding pair, requires the wavefunctions of the radiating and the perturbing molecules be known. Here the reduced matrix elements for collisions in the ground vibrational state of water vapor are calculated by two methods and compared. First, wavefunctions determined by diagonalizing an effective (Watson) Hamiltonian are used to calculate the RMEs and, second, the ab initio wavefunctions of Partridge and Schwenke are used. While the ground vibrational state will yield the best approximation of the wavefunctions from the effective Hamiltonian approach, this study clearly identifies problems for states not included in the fit of the Hamiltonian and for extrapolated states. RMEs determined using ab initio wavefunctions use ∼100000 times more computational time; however, all ro-vibrational interactions are included. Hence, the ab initio approach will yield better RMEs as the number of vibrational quanta exchanged in the optical transition increases, resulting in improvements in calculated half-widths and line shifts. It is important to note that even for pure rotational transitions the use of ab initio wavefunctions will yield improved results.

collection of articles based on oral presentation at the EUMETRISPEC workshop held at Wolfenbüttel castle and PTB Praunschweig, Nov. 15-16, 2012, PTB-Bericht Chemische Physik CP-8. ISSN 1614-953X. ISBN 978-3-95606-034-2., This PTB report comprises all oral presentations and posters presented at the Nov. 2012 workshop on "Spectral reference line data for atmospheric monitoring" held at Wolfenbüttel castle and PTB Braunschweig. The workshop was organized by the EUMETRISPEC project which is part of the European Metrology Research Programme (EMRP). The main aim was to present and discuss the stakeholders' views and needs. The stakeholders are from metrological organisations as well as from ground- and satellite-based monitoring networks and from quantum chemical modelling groups - in total 49 scientists representing 31 institutions from 12 nations. During the workshop, nine invited 45min-talks were given, covering spectroscopic and metrological key topics, accompanied by six additional presentations on EUMETRISPEC and the EMRP. The PTB report includes the authorized powerpoint presentations, as well as all 21 posters from 91 authors presented during the workshop.

The HITEMP database1 provides molecular spectroscopic parameters for high-temperature modeling of the spectra of molecules in the gas phase. Currently there are 5 molecular species on the database; H2O, CO2, CO, NO, OH. For H2O there are now transitions that have rotational quantum numbers up to J=50 and many transitions where the vibrational quantum numbers and prolate and oblate limit pseudo-quantum numbers (Ka and Kc) are not known. Line shape parameters are not available for most of these transitions. We have developed a method to determine these line shape parameters for the 3 most abundant isotopologues of water based on the Semi-empirical approach of Jacquemart etal.2 and an algorithm that estimates the number of vibrational quanta exchanged in the transition. Thus, vibrational dependence of the line shape parameters, which has been found to be important for H2O3, is taken into account for many transitions. When the parameters are not available from this new algorithm, average half-widhts as a function of J” are determined from a polynomial fit of validated calculated data. The results of the new algorithm and the J-averaged half-widths are compared with the values found on the 2008 version of the HITRAN database.

The submillimeter frequency coverage of the EOS-MLS aboard the Aura spacecraft has necessitated the measurement of a larger data set of air-broadened ozone linewidths at these wavelengths. An automated submillimeter spectrometer that utilizes directly synthesized radiation, programmable mass-flow controllers and a temperature controlled cell was implemented for expedient data collection of 17 diÆerent rotational transitions in the 620 - 660 GHz range. Many previous ozone rotational line-broadening studies have focused on single transitions, typically in the millimeter wavelengths, with the notable exception of a broadband FT-FIR study that characterized the J,Kc dependencies of many higher quanta states. The current measurements lie in a middle range of the pre- vious measurements and allow a more comprehensive picture of the J,Kc dependencies of linewidths over the entire ozone rotational band&nbsp