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Hans Ågren - One of the best experts on this subject based on the ideXlab platform.
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Two‐Photon Absorption Cross‐Sections of Reference Dyes: A Critical Examination
ChemPhysChem, 2008Co-Authors: Yan-hua Wang, Hans ÅgrenAbstract:The electronic structure and one- and two-photon Absorption spectra of four fluorophores, p-bis(o-methoxystyryl)benzene (Bis-MSB), coumarin 307, fluorescein and rhodamine B, commonly used as reference compounds for two-photon Absorption spectra, have been theoretically calculated and compared with available experimental data. The possible reasons for the wide discrepancies in two-photon Absorption Cross-Sections reported in the literature are discussed on the basis of the theoretical findings. The role of a solvent environment on the electronic one- and two-photon Absorption spectra is also studied. We highlight some necessary precautions that one needs to take when comparing literature results of two-photon Absorption Cross-Sections.
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calculations of two photon Absorption Cross Sections by means of density functional theory
Chemical Physics Letters, 2003Co-Authors: Yi Luo, Pawel Salek, Olav Vahtras, Jingdong Guo, Trygve Helgaker, Hans ÅgrenAbstract:We present density-functional theory and calculations for two-photon Absorption spectra of molecules. The two-photon Absorption Cross Sections are defined in terms of the single residues of the quadratic response function, which was recently derived for density-functional theory using the time-dependent variation principle and the quasi-energy ansatz. The Cross-section dependence on different functionals, including the general gradient approximation and hybrid theory, is examined for a set of small molecules. The results of hybrid density-functional theory compare favorably with those from singles-and-doubles coupled-cluster response calculations.
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effects of π centers and symmetry on two photon Absorption Cross Sections of organic chromophores
Journal of Chemical Physics, 2001Co-Authors: Chuankui Wang, Peter Macak, Yi Luo, Hans ÅgrenAbstract:We have theoretically examined a series of organic molecules that exhibit large two-photon Absorption Cross Sections in the visible region and that have been synthesized in different laboratories. One- and two-photon Absorption Cross Sections of the four lowest excited states of each molecule have been calculated at the same theoretical level using ab initio response theory. It is found that the molecular length and the one-photon Absorption intensity are quite strongly correlated factors, but that a corresponding correlation for the two-photon Absorption is much weaker or is missing. In contrast, a most crucial role for large two-photon Absorption is played by the π center. For molecules with a given π center a symmetrical structure with strong donor groups can result in a maximum two-photon Absorption Cross section. Our theoretical findings are consistent with some recent experimental observations. The chromophore based on dithienothiophene as π center attached with symmetrical N,N-diphenylamine donors is found to have the largest two-photon Cross section in the visible region among all known one-dimensional two-photon organic materials that have been reported in the literature.
Y J Chen - One of the best experts on this subject based on the ideXlab platform.
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vacuum uv spectroscopy of interstellar ice analogs ii Absorption Cross Sections of nonpolar ice molecules
arXiv: Solar and Stellar Astrophysics, 2014Co-Authors: G A Cruzdiaz, G Munoz M Caro, Y J Chen, T S YihAbstract:Dust grains in cold circumstellar regions and dark-cloud interiors at 10-20 K are covered by ice mantles. A nonthermal desorption mechanism is invoked to explain the presence of gas-phase molecules in these environments, such as the photodesorption induced by irradiation of ice due to secondary ultraviolet photons. To quantify the effects of ice photoprocessing, an estimate of the photon Absorption in ice mantles is required. In a recent work, we reported the vacuum-ultraviolet (VUV) Absorption Cross Sections of nonpolar molecules in the solid phase. The aim was to estimate the VUV-Absorption Cross Sections of nonpolar molecular ice components, including CH4, CO2, N2, and O2. The column densities of the ice samples deposited at 8 K were measured in situ by infrared spectroscopy in transmittance. VUV spectra of the ice samples were collected in the 120-160 nm (10.33-7.74 eV) range using a commercial microwave-discharged hydrogen flow lamp. We found that, as expected, solid N2 has the lowest VUV-Absorption Cross section, which about three orders of magnitude lower than that of other species such as O2, which is also homonuclear. Methane (CH4) ice presents a high Absorption near Ly-alpha (121.6 nm) and does not absorb below 148 nm. Estimating the ice Absorption Cross Sections is essential for models of ice photoprocessing and allows estimating the ice photodesorption rates as the number of photodesorbed molecules per absorbed photon in the ice.
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vacuum uv spectroscopy of interstellar ice analogs i Absorption Cross Sections of polar ice molecules
Astronomy and Astrophysics, 2014Co-Authors: G A Cruzdiaz, G Munoz M Caro, Y J ChenAbstract:Context. The vacuum-UV (VUV) Absorption Cross Sections of most molecular solids present in interstellar ice mantles with the exception of H2O, NH3 ,a nd CO 2 have not been reported yet. Models of ice photoprocessing depend on the VUV Absorption Cross section of the ice to estimate the penetration depth and radiation dose, and in the past, gas phase Cross section values were used as an approximation. Aims. We aim to estimate the VUV Absorption Cross section of molecular ice components. Methods. Pure ices composed of CO, H2O, CH3OH, NH3 ,o r H 2S were deposited at 8 K. The column density of the ice samples was measured in situ by infrared spectroscopy in transmittance. VUV spectra of the ice samples were collected in the 120−160 nm (10.33−7.74 eV) range using a commercial microwave-discharged hydrogen flow lamp. Results. We provide VUV Absorption Cross Sections of the reported molecular ices. Our results agree with those previously reported for H2 Oa nd NH 3 ices. Vacuum-UV Absorption Cross section of CH3OH, CO, and H2S in solid phase are reported for the first time. H2S presents the highest Absorption in the 120−160 nm range. Conclusions. Our method allows fast and readily available VUV spectroscopy of ices without the need to use a synchrotron beamline. We found that the ice Absorption Cross Sections can be very different from the gas-phase values, and therefore, our data will significantly improve models that simulate the VUV photoprocessing and photodesorption of ice mantles. Photodesorption rates of pure ices, expressed in molecules per absorbed photon, can be derived from our data.
Roger V. Yelle - One of the best experts on this subject based on the ideXlab platform.
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New benzene Absorption Cross Sections in the VUV, relevance for Titan’s upper atmosphere
Icarus, 2016Co-Authors: Fernando J. Capalbo, Yves Bénilan, Nicolas Fray, Martin Schwell, Norbert Champion, Et-touhami Es-sebbar, Tommi T. Koskinen, Lehocki Ivan, Roger V. YelleAbstract:Benzene is an important molecule in Titan’s atmosphere because it is a potential link between the gas phase and the organic solid phase. We measured photoAbsorption in the ultraviolet by benzene gas at temperatures covering the range from room temperature to 215 K. We derived benzene Absorption Cross Sections and analyzed them in terms of the transitions observed. No significant variation with measurement temperature was observed. We discuss the implications of our measurements for the derivation of benzene abundance profiles in Titan’s thermosphere, by the Cassini/Ultraviolet Imaging Spectrograph (UVIS). The use of Absorption Cross Sections at low temperature is recommended to avoid small systematic uncertainties in the profiles. We used our measurements, together with Absorption Cross Sections from other molecules, to analyze four stellar occultations by Titan, measured by UVIS during flybys T21, T41, T41_II, and T53. We derived and compared benzene abundance profiles in Titan’s thermosphere between approximately 530 and 1000 km, for different dates and geographical locations. The comparisons of our benzene profiles with each other, and with profiles from models of the upper atmosphere, point to a complex behavior that is not explained by current photochemical models.
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new benzene Absorption Cross Sections in the vuv relevance for titan s upper atmosphere
Icarus, 2016Co-Authors: Fernando J. Capalbo, Yves Bénilan, Nicolas Fray, Martin Schwell, Norbert Champion, Ettouhami Essebbar, Tommi Koskinen, Ivan Lehocki, Roger V. YelleAbstract:Benzene is an important molecule in Titan’s atmosphere because it is a potential link between the gas phase and the organic solid phase. We measured photoAbsorption in the ultraviolet by benzene gas at temperatures covering the range from room temperature to 215 K. We derived benzene Absorption Cross Sections and analyzed them in terms of the transitions observed. No significant variation with measurement temperature was observed. We discuss the implications of our measurements for the derivation of benzene abundance profiles in Titan’s thermosphere, by the Cassini/Ultraviolet Imaging Spectrograph (UVIS). The use of Absorption Cross Sections at low temperature is recommended to avoid small systematic uncertainties in the profiles. We used our measurements, together with Absorption Cross Sections from other molecules, to analyze four stellar occultations by Titan, measured by UVIS during flybys T21, T41, T41_II, and T53. We derived and compared benzene abundance profiles in Titan’s thermosphere between approximately 530 and 1000 km, for different dates and geographical locations. The comparisons of our benzene profiles with each other, and with profiles from models of the upper atmosphere, point to a complex behavior that is not explained by current photochemical models.
Johannes Orphal - One of the best experts on this subject based on the ideXlab platform.
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revised ultraviolet Absorption Cross Sections of h2co for the hitran database
Journal of Quantitative Spectroscopy & Radiative Transfer, 2011Co-Authors: Kelly Chance, Johannes OrphalAbstract:Abstract A revised set of temperature-dependent Absorption Cross Sections for ultraviolet (UV) measurements of formaldehyde (H2CO) has been derived from two existing sets of laboratory Cross Sections, one using a Fourier transform spectrometer (FTS), and one using a grating instrument. This is conducted to satisfy the recommendation of the HITRAN Advisory Committee to provide a dataset with the spectral resolution and wavelength calibration of Fourier transform spectrometer measurements with the better intensity calibration that the grating measurements obtained. The re-scaled Cross Sections are now in the HITRAN database, and are recommended for use in atmospheric measurements and modeling, including photolysis calculations.
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Ultraviolet and visible Absorption Cross-Sections for HITRAN
Journal of Quantitative Spectroscopy & Radiative Transfer, 2003Co-Authors: Johannes Orphal, Kelly ChanceAbstract:Ultraviolet-visible Absorption Cross-Sections are important reference data for remote sensing of atmospheric trace gases including O3; NO2; BrO; H2CO; OClO; SO2, and NO3 using optical instruments. In this paper, the reference Absorption Cross-Sections for the HITRAN database are presented and needs for future improvements are addressed. ? 2003 Elsevier Ltd. All rights reserved.
Kelly Chance - One of the best experts on this subject based on the ideXlab platform.
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revised ultraviolet Absorption Cross Sections of h2co for the hitran database
Journal of Quantitative Spectroscopy & Radiative Transfer, 2011Co-Authors: Kelly Chance, Johannes OrphalAbstract:Abstract A revised set of temperature-dependent Absorption Cross Sections for ultraviolet (UV) measurements of formaldehyde (H2CO) has been derived from two existing sets of laboratory Cross Sections, one using a Fourier transform spectrometer (FTS), and one using a grating instrument. This is conducted to satisfy the recommendation of the HITRAN Advisory Committee to provide a dataset with the spectral resolution and wavelength calibration of Fourier transform spectrometer measurements with the better intensity calibration that the grating measurements obtained. The re-scaled Cross Sections are now in the HITRAN database, and are recommended for use in atmospheric measurements and modeling, including photolysis calculations.
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Ultraviolet and visible Absorption Cross-Sections for HITRAN
Journal of Quantitative Spectroscopy & Radiative Transfer, 2003Co-Authors: Johannes Orphal, Kelly ChanceAbstract:Ultraviolet-visible Absorption Cross-Sections are important reference data for remote sensing of atmospheric trace gases including O3; NO2; BrO; H2CO; OClO; SO2, and NO3 using optical instruments. In this paper, the reference Absorption Cross-Sections for the HITRAN database are presented and needs for future improvements are addressed. ? 2003 Elsevier Ltd. All rights reserved.
