1,721,021 research outputs found
NEW MEASUREMENTS OF THE WATER VAPOR ABSORPTION CROSS SECTION IN THE BLUE-VIOLET RANGE BY CAVITY-ENHANCED DIFFERENTIAL OPTICAL ABSORPTION SPECTROSCOPY
No full textThe absorption cross section of water vapor in the blue-violet range (415-460 nm) is currently not well known, and many weak spectral lines are not included in either the HIgh resolution TRANsmission molecular absorption (HITRAN) database or its HIgh TEMPerature companion, HITEMP. Direct measurements of the absorption cross section of water vapor in this region have been limited by the slant column density (SCD) of gaseous water molecules achievable in a laboratory setting. We use cavity-enhanced differential optical absorption spectroscopy (CE-DOAS) to generate water vapor SCDs comparable to those in field measurements. Our cavity consists of high-reflectivity (R 0.99995) mirrors separated by ~80 cm to realize effective path lengths up to 16 km; water vapor is generated from deionized water in a double-bubbler system. Broadband light sources (LEDs) with peak intensities at 420 and 455 nm allow us to measure multiple lines at moderately high spectral resolution (0.15 nm). The first spectra were measured at room temperature (298 K), but our setup allows us to explore temperature variations.
Our goals are to refine available line lists for gas-phase water by combining laboratory measurements with quantum chemical calculations, and to reevaluate field measurements. In particular, we will revisit field data from University of Colorado Airborne Multi-AXis Differential Optical Absorption Spectroscopy (CU AMAX-DOAS) instrument during the Tropical Ocean tRoposphere Exchange of Reactive halogen species and Oxygenated VOC (TORERO) campaign. As part of TORERO, comparisons of in situ and remote-sensing measurements of water vapor were performed, and AMAX-DOAS fits exhibited cosmetic residual structures when using HITRAN and HITEMP reference spectra. Our work has the potential to improve trace gas retrievals from many current and planned satellites, e.g. Ozone Monitoring Instrument (OMI), TROPOspheric Monitoring Instrument (TROPOMI), and Tropospheric Emissions: Monitoring of Pollution (TEMPO); and from aircraft-based remote-sensing instruments such as the CU AMAX-DOAS
New measurements of the water vapor absorption cross section in the blue-violet range by cavity-enhanced differential optical absorption spectroscopy
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Previous issue date: 6The absorption cross section of water vapor in the blue-violet range (415-460 nm) is currently not well known, and many weak spectral lines are not included in either the HIgh resolution TRANsmission molecular absorption (HITRAN) database or its HIgh TEMPerature companion, HITEMP. Direct measurements of the absorption cross section of water vapor in this region have been limited by the slant column density (SCD) of gaseous water molecules achievable in a laboratory setting. We use cavity-enhanced differential optical absorption spectroscopy (CE-DOAS) to generate water vapor SCDs comparable to those in field measurements. Our cavity consists of high-reflectivity (R > 0.99995) mirrors separated by 80 cm to realize effective path lengths up to 16 km; water vapor is generated from deionized water in a double-bubbler system. Broadband light sources (LEDs) with peak intensities at 420 and 455 nm allow us to measure multiple lines at moderately high spectral resolution (0.15 nm). The first spectra were measured at room temperature (298 K), but our setup allows us to explore temperature variations.
Our goals are to refine available line lists for gas-phase water by combining laboratory measurements with quantum chemical calculations, and to reevaluate field measurements. In particular, we will revisit field data from University of Colorado Airborne Multi-AXis Differential Optical Absorption Spectroscopy (CU AMAX-DOAS) instrument during the Tropical Ocean tRoposphere Exchange of Reactive halogen species and Oxygenated VOC (TORERO) campaign. As part of TORERO, comparisons of in situ and remote-sensing measurements of water vapor were performed, and AMAX-DOAS fits exhibited cosmetic residual structures when using HITRAN and HITEMP reference spectra. Our work has the potential to improve trace gas retrievals from many current and planned satellites, e.g. Ozone Monitoring Instrument (OMI), TROPOspheric Monitoring Instrument (TROPOMI), and Tropospheric Emissions: Monitoring of Pollution (TEMPO); and from aircraft-based remote-sensing instruments such as the CU AMAX-DOAS
A HIGHLY ACCURATE AB INITIO DIPOLE MOMENT SURFACE FOR WATER: TRANSITIONS EXTENDING INTO THE ULTRAVIOLET
No full textWe present a new \textit{ab initio} dipole moment surface (DMS) for the
water molecule valid for transitions which stretch into the near ultraviolet.
Intensities computed using this surface
agree very well with precise laboratory measurements designed
to aid atmospheric observations. This work is based on a data set
encompassing 17 628 multi-reference configuration interaction
configurations that were calculated with the aug-cc-pCV6Z basis set
with the Douglass-Kroll-Hess Hamiltonian to second order and
required approximately 116 years of CPU running time to complete.
Compared to recent experimental measurements in the far infrared
region\footnote{M. Birk {et al.}, J. Quant. Spectrosc. Rad. Transf,
203, 88-102 (2017)}, this new DMS significantly improves agreement
with theory for transitions in the previously problematic bands
(121), (300) and (102). For highly energetic overtones located in
both the visible and ultraviolet regimes, we successfully predict
the intensity of all measured bands to within 10\% of the latest atmospheric
observations\footnote{ J. Lampel {et al.}, Atmos. Chem. Phys, 17,
1271-1295, (2017)}. These include bands at 487 nm (303), 471 nm
(511), and 363 nm (900), for which previous models underestimated the
intensity by up
to 139\%. Absorption features are also predicted in the 290 nm to
355 nm window and the theoretical shape demonstrates reasonably good
behaviour with previously measured cross sections. The 10
band is identified as the strongest absorber in this region and the
maximum intensity is approximately cm per
molecule, which should be observable in atmospheric spectra
A highly accurate ab initio dipole moment surface for water: Transitions extending into the ultraviolet
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Previous issue date: 6We present a new ab initio dipole moment surface (DMS) for the water molecule valid for transitions which stretch into the near ultraviolet. Intensities computed using this surface agree very well with precise laboratory measurements designed to aid atmospheric observations. This work is based on a data set encompassing 17 628 multi-reference configuration interaction configurations that were calculated with the aug-cc-pCV6Z basis set with the Douglass-Kroll-Hess Hamiltonian to second order and required approximately 116 years of CPU running time to complete.
Compared to recent experimental measurements in the far infrared regionb , this new DMS significantly improves agreement with theory for transitions in the previously problematic bands (121), (300) and (102). For highly energetic overtones located in both the visible and ultraviolet regimes, we successfully predict the intensity of all measured bands to within 10% of the latest atmospheric observationsc . These include bands at 487 nm (303), 471 nm (511), and 363 nm (900), for which previous models underestimated the intensity by up to 139%. Absorption features are also predicted in the 290 nm to 355 nm window and the theoretical shape demonstrates reasonably good behaviour with previously measured cross sections. The 10 ν1 band is identified as the strongest absorber in this region and the maximum intensity is approximately 6.3 × 10−27 cm per molecule, which should be observable in atmospheric spectra
ANALYSIS OF HOT MOLECULAR SPECTRA
No full textAuthor Institution: Department of Physics and Astronomy, University College LondonRecent increases in accuracy of triatomic molecular energy level calculations for high rotational quantum numbers J is reviewed. Variational calculations which use exact kinetic energy operators can treat all vibrational states simultaneously. These calculations can use high quality ab initio and fitted potential energy surfaces. For spectroscopic accuracy on hydrogen containing molecules, it is necessary to include adiabatic and nonadiabatic corrections to the Born-Oppenheimer approximation. Relativistic corrections can also be important. Application of the resulting calculations of energy levels and spectra to the analysis of seemingly unassignable spectra of water and is described. Spectra of water in sunspot , laboratory and even room temperature contain hundreds or thousands of lines which remained unassigned for more than a decade (see for example Polyansky et al., Science, v. 277, N5324, pp. 346-348 (1997)). We present here the results of the assignments of these water lines. line assignment is also considered as well as progress on and the analysis of the spectra of other triatomic molecules
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Extra high accuracy fitting of the PES for sub-percent calculation of intensities
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Previous issue date: 6Calculation of rotation-vibration line intensities with sub-percent accuracy has recently become a standard requirement for the applications in retrieval and monitoring of gases in the Earth’s atmosphere and potentially in the atmospheres of exoplanets. A major factor in the accurate calculation of intensities is the requirement for a high accuracy ab initio Dipole moment surface (DMS) (e.g. references a and b ). We demonstrate here that the change from the ”good” potential energy surface (PES) to ”excellent” PES, used for the intensity calculations is also important. By ”good” we mean here, for example, the PES a standard deviation of 0.025 cm−1 and by ”excellent” - the PES with the standard deviation 0.011 cm−1 . Details of studies on H2Oc , O3 d , HCN and CO2 molecules will be presented in the talk
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