| 1. |
- Eilers, Gerriet, et al.
(författare)
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The Radiocarbon Intracavity Optogalvanic Spectroscopy Setup at Uppsala
- 2013
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Ingår i: Radiocarbon. - : Cambridge University Press (CUP). - 0033-8222 .- 1945-5755. ; 55:3-4, s. 237-250
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Tidskriftsartikel (refereegranskat)abstract
- Accelerator mass spectrometry (AMS) is by far the predominant technology deployed for radiocarbon tracer studies. Applications are widespread from archaeology to biological, environmental, and pharmaceutical sciences. In spite of its excellent performance, AMS is expensive and complicated to operate. Consequently, alternative detection techniques for 14C are of great interest, with the vision of a compact, user-friendly, and inexpensive analytical method. Here, we report on the use of intracavity optogalvanic spectroscopy (ICOGS) for measurements of the 14C/12C ratio. This new detection technique was developed by Murnick et al. (2008). In the infrared (IR) region, CO2 molecules have strong absorption coefficients. The IR-absorption lines are narrow in line width and shifted for different carbon isotopes. These properties can potentially be exploited to detect 14CO2, 13CO2, or 12CO2 molecules unambiguously. In ICOGS, the sample is in the form of CO2 gas, eliminating the graphitization step that h is required in most AMS labs. The status of the ICOGS setup in Uppsala is presented. The system is operational but not yet fully developed. Data are presented for initial results that illustrate the dependence of the optogalvanic signal on various parameters, such as background and plasma-induced changes in the sample gas composition.
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| 2. |
- Opanasyuk, Oleg, 1971-, et al.
(författare)
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On the analyses of fluorescence depolarisation data in the presence of electronic energy migration. : II. Applying & Evaluating Two-Photon Excited Fluorescence
- 2012
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076 .- 1463-9084. ; 14, s. 1917-1922
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Tidskriftsartikel (refereegranskat)abstract
- Electronic energy migration within a bifluorophoric molecule has been studied by time-resolved two-photon excited (TPE) fluorescence depolarisation experiments. Data were analysed by using a recently developed quantitative approach [Opanasyuk, O. & Johansson, L. B.-Å., On the Analyses of Fluorescence Depolarisation Data in the Presence of Electronic Energy Migration. I. Theory & General Description. Phys. Chem. Chem. Phys., Submitted.]. The energy migration occurs between the 9-anthrylmethyl groups of the bifluorophoric molecule, bis-(9-anthrylmethylphosphonate) bisteroid. These groups undergo local reorientations, while overall tumbling of the bisteroid is strongly hampered in the used viscous solvent, 1,2-propanediol. To solely obtain information about local reorientations of the 9-anthrylmethyl group, also the mono-(9-anthrylmethylphosphonate) bisteroid was studied, which enabled modelling of the ordering potential shape. The analysis of data is partly performed in the Fourier domain and the best-fit parameters are determined by using an approach based on a Genetic Algorithm. The energy migration process was described by an extended Förster theory (EFT). A reasonable value of the distance between the 9-anthrylmethyl groups is found, as well as for the mutual orientation of the ordering potentials. Furthermore, values of the two-photon tensor components were obtained.
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| 3. |
- Opanasyuk, Oleg, et al.
(författare)
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On the analyses of fluorescence depolarisation data in the presence of electronic energy migration. Part II : Applying and evaluating two-photon excited fluorescence
- 2012
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 14:6, s. 1917-1922
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Tidskriftsartikel (refereegranskat)abstract
- Electronic energy migration within a bifluorophoric molecule has been studied by time-resolved two-photon excited (TPE) fluorescence depolarisation experiments. Data were analysed by using a recently developed quantitative approach [O. Opanasyuk and L. B.-A. Johansson, On the Analyses of Fluorescence Depolarisation Data in the Presence of Electronic Energy Migration. Part I: Theory and General Description, Phys. Chem. Chem. Phys., submitted]. The energy migration occurs between the 9-anthrylmethyl groups of the bifluorophoric molecule, bis-(9-anthrylmethylphosphonate) bisteroid. These groups undergo local reorientations, while overall tumbling of the bisteroid is strongly hampered in the used viscous solvent, 1,2-propanediol. To solely obtain information about local reorientations of the 9-anthrylmethyl group, also the mono-(9-anthrylmethylphosphonate) bisteroid was studied, which enabled modelling of the ordering potential shape. The analysis of data is partly performed in the Fourier domain and the best-fit parameters are determined by using an approach based on a Genetic Algorithm. The energy migration process was described by an extended Forster theory (EFT). A reasonable value of the distance between the 9-anthrylmethyl groups, as well as for the mutual orientation of the ordering potentials, is found. Furthermore, values of the two-photon tensor components were obtained.
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| 4. |
- Opanasyuk, Oleg, 1971-, et al.
(författare)
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Two-photon excited fluorescence depolarisation and electronic energy migration within donor–donor pairs
- 2009
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; :11, s. 7152-7160
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Tidskriftsartikel (refereegranskat)abstract
- A unified theoretical description is presented for one- and two-photon excited fluorescence depolarisation and electronic energy migration within pairs of chromophores. Two weakly coupled donor groups are linked via a rigid macromolecule with the ability to undergo restricted reorienting motions. Describing these reorienting motions as well as their influence on the coupling is rather complex, but can be accounted for by using the extended Förster theory. Here explicit expressions have been derived for chromophores belonging to the point groups D2h,D2 andC2v when residing in uniaxial potentials (i.e. C∞v symmetry). From the given basic equations, it is possible however, to derive the relevant equations for molecules of arbitrary symmetry in any uniaxial orienting potential. The expected time-resolved fluorescence anisotropy for different two-photon absorption tensors are compared for reorienting fluorophores in liquids, as well as in anisotropic systems. Simulated fluorescence depolarisation data are also displayed that mimic energy migration within pairs of two-photon excited donor molecules, which simultaneously undergo reorienting motions within effectively isotropic and uniaxially anisotropic environments. The obtained results demonstrate that the time-resolved fluorescence anisotropy strongly depends on the properties of the two-photon absorption tensor, as well as on using a linear or a circular polarisation of the excitation field.
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| 5. |
- Persson, Anders, et al.
(författare)
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Evaluation of Intracavity Optogalvanic Spectroscopy for Radiocarbon Measurements
- 2013
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Ingår i: Analytical Chemistry. - : American Chemical Society (ACS). - 0003-2700 .- 1520-6882. ; 85ASAP:14, s. 6790-6798
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Tidskriftsartikel (refereegranskat)abstract
- Ever since the first publication of intracavity optogalvanic spectroscopy (ICOGS) in 2008, this novel technique for measuring the 14C/12C ratio in carbon dioxide has rendered considerable attention. As a result, there are currently at least five different research groups pursuing research on ICOGS. With a claimed limit of detection of 10–15 (14C/12C), i.e., in the same order as accelerator mass spectroscopy, achieved with a relatively inexpensive and uncomplicated table-top system, ICOGS has major scientific and commercial implications. However, during the past 5 years, no research group has been able to reproduce these results or present additional proof for ICOGS’s capability of unambiguous 14C detection, including the authors of the original publication. Starting in 2010, our group has set up a state-of-the-art ICOGS laboratory and has investigated the basic methodology of ICOGS in general and tried to reproduce the reported experiments in particular. We have not been able to reproduce the reported results concerning the optogalvanic signals dependence on14C concentration and wavelength and, ultimately, not seen any evidence of the capability of ICOGS to unambiguously detect 14C at all. Instead, we have found indications that the reported results can be products of measurement uncertainties and mistakes. Furthermore, our results strongly indicate that the reported limit of detection is likely to be overestimated by at least 2 orders of magnitude, based on the results presented in the original publication. Hence, we conclude that the original reports on ICOGS cannot be confirmed and therefore must be in error.
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| 6. |
- Ryderfors, Linus, et al.
(författare)
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Excited-state symmetry and reorientation dynamics of perylenes in liquid solutions : Time-resolved fluorescence depolarization studies using one- and two-photon excitation
- 2008
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 112:26, s. 5794-5803
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Tidskriftsartikel (refereegranskat)abstract
- The excited-state symmetry and molecular reorientation of perylene, 1,7-diazaperylene, and 2,5,8,1 1-tetratert-butylperylene have been studied by different fluorescence depolarization experiments. The first excited electronic singlet state was reached through one-photon excitation (OPE) and two-photon excitation (TPE). A 400 and 800 nm femtosecond laser pulse was used for this purpose, and data were collected by means of the time-correlated single-photon counting technique. It is found that the rotational correlation times for each perylene derivative are very similar in the OPE and TPE depolarization experiments. For the determination of the two-photon absorption tensor, a recently described theoretical model has been applied (Ryderfors et al. J. Phys. Chem. A 2007, 111, 11531). It was found that the two-photon process can be described by a 2 x 2 absorption tensor for which the components are solvent dependent and exhibit mixed vibronic character. In the dipole approximation this is compatible with a parity-forbidden two-photon absorption into the first excited singlet state.
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| 7. |
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| 8. |
- Ryderfors, Linus, et al.
(författare)
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The Symmetry of Two-Photon Excited States as Determined by Time-Resolved Fluorescence Depolarisation Experiments
- 2007
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 111:45, s. 11531-11539
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Tidskriftsartikel (refereegranskat)abstract
- A new experimental and theoretical approach is presented for the quantitative determination and assignment of the two-photon absorption tensor of fluorophores dissolved in liquid solutions. Two linearly independent time-resolved fluorescence anisotropies and the two-photon polarization ratio were determined from experiments based on using the time-correlated single photon counting technique. The data were analyzed in a global manner under the assumption of prevailing diffusive molecular reorientations and when accounting for the influence of rapid unresolved reorientations. The method has been applied in fluorescence studies of perylene, two-photon excited at 800 nm. The analysis suggests that the two-photon transition is mediated via vibronic coupling including at least two vibrations of different symmetry, and also that the first singlet excited electronic state acts as a dominating intermediate state.
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| 9. |
- Ryderfors, Linus, et al.
(författare)
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Two-Photon Excited Fluorescence and Molecular Reorientations in Liquid Solutions
- 2007
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Ingår i: Journal of Fluorescence. - : Springer Science and Business Media LLC. - 1053-0509 .- 1573-4994. ; 17:5, s. 466-480
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Tidskriftsartikel (refereegranskat)abstract
- Theoretical expressions are derived that relate the two-photon excited fluorescence depolarisation experiments to the molecular symmetry and the rotational motions of fluorescent molecules. Diffusive rotational motions in liquid solvents are considered, as well as the influence of fast unresolved motions (e.g. librations). The results obtained are compared with one-photon excited fluorescence depolarisation experiments. The derived theoretical expressions can be applied for detailed analyses of the molecular rotation in solvent. Several of the results are useful for determining and assigning the components of two-photon absorption tensors.
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| 10. |
- Ryderfors, Linus, 1977-
(författare)
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Two-Photon Excited Fluorescence Depolarisation : Experimental and Theoretical Development
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- We have studied fundamental aspects of time-resolved two-photon excited fluorescence depolarisation. The thesis presents experimental as well as theoretical progress. We show that a multi-photon induced instrumental response function obtained from a suspension of gold nanoparticles is appropriate for the analysis of two-photon excited fluorescence decays obtained using time-correlated single photon counting detection. Theoretical expressions have been derived for the fluorescence anisotropy decay obtained upon two-photon excitation of various molecular systems in liquid solutions: a) an anisotropic rigid rotor that undergoes rotational diffusion in the presence of ultrafast unresolved restricted reorientations, e.g. librations. b) a molecular group covalently attached to a stationary macromolecule, and undergoing local reorientation in a uniaxial ordering potential. A new approach to the analysis of two-photon excited fluorescence depolarisation experiments was developed, which combines data obtained by using linearly and circularly polarised excitation light, in a global manner. In the analysis, knowledge about unresolved reorientations was obtained from one-photon excitation studies of the corresponding systems. By means of this procedure it has been possible to obtain quantitative information about the molecular two-photon absorption tensor for perylene and two of its derivatives. Thereby the symmetry of the final excited and intermediate vibronic states could be assigned. The analysis reveals that the two-photon transition studied with the 800 nm laser exhibits mixed character. An important finding from the experiments was that the two-photon absorption tensor appears to be solvent dependent. Furthermore, the thesis presents the first theoretical treatment of two-photon excited donor-donor energy migration in the presence of molecular reorientation and which applies the extended Förster theory. Explicit expressions for molecules that belong to the point groups D2h, D2 and C2v are given. Preliminary experiments are finally also reported on a two-photon excited donor-donor energy migration system consisting of a bisanthryl-bisteroid.
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