E. Akesson - Academia.edu (original) (raw)
Papers by E. Akesson
Conference Digest. 2000 International Quantum Electronics Conference (Cat. No.00TH8504)
Summary form only given. Much effort has been put into understanding the photodissociation dynami... more Summary form only given. Much effort has been put into understanding the photodissociation dynamics of dihalomethanes in the gas phase. In solution, the task is even more challenging since supplementary processes can be present in the condensed phase; one such example is geminate recombination within the cage of solvent molecules. We present observations of the isomers for dihalomethanes, with particular
Technical Digest. 1998 EQEC. European Quantum Electronics Conference (Cat. No.98TH8326)
We present here ow new experimental and theoretical results concerning the low frequency boats in... more We present here ow new experimental and theoretical results concerning the low frequency boats in several polymnethtne dyes. Our studies show that the iduence of the solvation dynamica on the beat behavior is not reduced only to the time evolution of the chromophore spectra (the increare in beem contrast due to the haleburning eZZ is available. "-zJdFF(fi *laon where $(.) is the nuclear part of the polsrizat.ion operalor of the solvent and B(F,z) is the electric firld creat.ed by the solute inoleculc For the dipole cont.ribi~tian, VIsa = &s (e),. The fit. of the erperimerrtal date by the model developed in thts study is very good for all solvents
The Bologna process is a voluntary joint venture among 46 European countries, which has as its ob... more The Bologna process is a voluntary joint venture among 46 European countries, which has as its objective the creation of a European Higher Education Area (EHEA) by 2010. The EHEA will cover all of Europe including European Union newcomers Armenia, Azerbaijan, Georgia, Moldova, and Ukraine. Its aim is to allow for degrees and qualifications awarded in one country to be understood and recognized in other countries, thereby facilitating mobility and enhancing employability. The EHEA's overarching goals will be achieved by providing common tools and fostering cooperation in quality assurance. The common tools in the emerging EHEA, such as the European Credit Transfer and Accumulation System, Diploma supplement, a three-cycle system, and qualification frameworks, all aim to provide a system that is easy to comprehend for students, institutions, and employers.
SPIE Proceedings, 1992
We have made ultrafast time resolved pump probe measurements on the intramolecular electron trans... more We have made ultrafast time resolved pump probe measurements on the intramolecular electron transfer (ET) of the betaines, specifically betaine30 and penta-t-butyl betaine. The data have been analyzed to determine the ET rate in a range of solvent environments, at various temperatures and at a variety of pump and probe wavelengths. In all cases, the observed ET rate is fast, often faster than predicted by common ET theories. As a result, we have extended some common theories to successfully predict the measured ET rates. In addition to the ET dynamics, the data also display evidence for local heat deposition in the immediate vicinity of the betaine molecule which our extended model qualitatively predicts.
The Journal of Physical Chemistry A, 2002
ABSTRACT We studied the A-band photodissociation of bromoiodomethane, CH2BrI, in acetonitrile sol... more ABSTRACT We studied the A-band photodissociation of bromoiodomethane, CH2BrI, in acetonitrile solution at room temperature by femtosecond pump−probe spectroscopy. Initiated by the 266 nm light, this reaction leads to the CH2Br−I isomer, most likely produced via in-cage recombination of the CH2Br and I photofragments. The isomer is formed vibrationally excited with a time constant of 7.5 ps and the hottest isomer molecules are observed as early as 1 ps after the UV excitation. Vibrational relaxation of the isomer molecules takes place on two distinct time scales of a few and 40 ps. The ground-state lifetime of the isomer is about 2.5 ns.
The Journal of Chemical Physics, 1991
Reproduction in A iole or in part is permitted for any purpose of the United States Government. T... more Reproduction in A iole or in part is permitted for any purpose of the United States Government. This document has been appproved for public release and sale, its distribution is unlimited.
The Journal of Chemical Physics, 1992
The inverted regime photoinduced electron transfer kinetics of betaine-30 have been investigated ... more The inverted regime photoinduced electron transfer kinetics of betaine-30 have been investigated over a broad teiaperature range, revealing very little temperature dependence.
FEBS Letters, 2000
The transient absorption anisotropy spectrum of bacteriochlorophyll a (BChl a) in pyridine was me... more The transient absorption anisotropy spectrum of bacteriochlorophyll a (BChl a) in pyridine was measured in the wavelength interval 550^850 nm, 1 ps after optical excitation with a 792-nm femtosecond light pulse. In the wavelength region of Q y absorption and stimulated emission (775^825 nm), the anisotropy was found to be close to the theoretically expected value (0.4) for a two-level system. In the wavelength region 6507 50 nm, where the transient absorption signal is dominated by excited state absorption, the anisotropy is reduced to V V0.18. Anisotropy kinetics were measured at several wavelengths and found to be constant within the time window 0^5 ps, showing that no internal dynamics of the BChl a molecule change the anisotropy on the time scale of tens of picoseconds.
… C/C OF PIS'MA V …, 1993
... SV Chekalin and VM Farztdinov , Institute of Spectroscopy, Russian Academy of Sciences, 14209... more ... SV Chekalin and VM Farztdinov , Institute of Spectroscopy, Russian Academy of Sciences, 142092 Troitsk, Moscow Oblast, Russia E. Âkesson and V. Sundström University of ... Thomas et al.10 studied the relaxation of excited carriers in а Сбо film by absorption spectroscopy. ...
Chemical Physics Letters, 2005
The energy transfer within a series of Zn-porphyrin appended dendrimers was studied by means of t... more The energy transfer within a series of Zn-porphyrin appended dendrimers was studied by means of time-resolved fluorescence anisotropy. We show that the energy transfer process between the Zn-porphyrin units in the dendrimers is limited to a maximum of four porphyrin units. At 200 K, the energy transfer process takes place on a 100-ps time scale, and can be modeled by Fö rster theory. Our results at room temperature further show that the porphyrin units are very mobile within the dendrimer, exhibiting rotational dynamics similar to that of a monomeric building block.
Chemical Physics Letters, 2006
Solvent induced optimization of energy transfer properties in a series of Zn(II)-porphyrin-append... more Solvent induced optimization of energy transfer properties in a series of Zn(II)-porphyrin-appended dendrimers has been studied by means of excitonexciton annihilation. Upon changing from a polar solvent (tetrahydrofuran) to a non-polar solvent (3-methyl-pentane), the ...
Chemical Physics Letters, 2001
The photodissociation dynamics of iodo-, bromo-and chlorobenzene upon excitation at 266 nm have b... more The photodissociation dynamics of iodo-, bromo-and chlorobenzene upon excitation at 266 nm have been studied by femtosecond pump-probe spectroscopy combined with time-of-¯ight (TOF) mass spectrometric detection. The kinetics are characterized by a single time constant for chlorobenzene (1 ns) and bromobenzene (28 ps), and by two time constants for iodobenzene (700 and 350 fs). The time constant of 350 fs is due to direct dissociation. The increase of the other time constants with decreasing halogen mass supports the assignment of these constants to the decay of the initially excited p; p à states to the repulsive triplet n; r à state due to spin±orbit coupling.
Biophysical Journal, 1995
Energy transfer within the peripheral light-harvesting antenna of the purple bacteria Rhodobacter... more Energy transfer within the peripheral light-harvesting antenna of the purple bacteria Rhodobacter sphaeroides and Rhodopseudomonas palustris was studied by one-and two-color pump-probe absorption spectroscopy with-1 00-fs tunable pulses at room temperature and at 77 K. The energy transfer from B800 to B850 occurs with a time constant of 0.7 + 0.05 ps at room temperature and 1.8 ± 0.2 ps at 77 K and is similar in both species. Anisotropy measurements suggest a limited but fast B800 <-> B800 transfer time (0.3 ps). This is analyzed as incoherent hopping of the excitation in a system of spectrally inhomogeneous antenna pigment-protein complexes, by a master equation approach. The simulations show that the measured B800 dynamics is well described as energy transfer with a characteristic average nearest-neighbor pairwise transfer time of 0.35 ps among-10 Bchl molecules in a circular arrangement, in good agreement with the recent high-resolution structure of LH2. The possible presence of fast intramolecular relaxation processes within the Bchl a molecule was investigated by measurement of time-resolved difference absorption spectra and kinetics of Bchl a in solution and in low-temperature glasses. From these measurements it is concluded that fast transients observed at room temperature are due mainly to solvation processes, whereas at 77 K predominantly slower (>10-ps) relaxation occurs.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1986
Excitation-energy transport in the bacteriochlorophyll antenna systems of Rhodospirillum rubrum a... more Excitation-energy transport in the bacteriochlorophyll antenna systems of Rhodospirillum rubrum and Rhodobacter sphaeroides, studied by low-intensity picosecond absorption spectroscopy
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1986
The Journal of Chemical Physics, 1991
In this work we have studied the isomerization dynamics of a cyanine dye molecule in solution. Th... more In this work we have studied the isomerization dynamics of a cyanine dye molecule in solution. The viscosity and temperature dependencies of the isomerization rate have been measured in the series of n-alcohols for three different sizes of the isomerizing group. From these measurements we conclude that the shear viscosity of the solvent is not a good measure of the
Chemical Physics Letters, 1986
The photoi~me~~tion dynamics of the dyes pinacyanol, l,l'-diethyl-4,4'-cyanine and t-stilbene in ... more The photoi~me~~tion dynamics of the dyes pinacyanol, l,l'-diethyl-4,4'-cyanine and t-stilbene in n-alcohol solutions has been studied by picosecond absorption spectroscopy. The dyes are found to isomerize without any potential barrier in the excited state. The viscosity and temperature dependence of the relaxation rates of pinacyanol and t-stilbene agree with predictions of theoretical models, whereas for 1,1'-4,4'-cyanine more complex behaviour is observed and possible reasons discussed. An excitation wavelength dependence of the isomerization rate for l,l'-4,4'-cyanine was also observed; the isomerization lifetime varies by a factor 2-3 over the absorption band. Such a dependence is predicted from the theoretical models.
Chemical Physics Letters, 2003
The photodissociation of bromobenzene in solution was investigated with ultrafast transient absor... more The photodissociation of bromobenzene in solution was investigated with ultrafast transient absorption spectroscopy following excitation at 266 nm. Ab initio calculations of lower singlet and triplet states were performed in order to guide the interpretations. The main feature of the kinetics measured between 300 and 930 nm in acetonitrile is a 9 AE 1 ps decay, which we mainly assign to predissociation. Similar decays were observed in hexane, dichloromethane and tetrachloromethane at 400 and 800 nm. Other features in acetonitrile, such as complicated short-time dynamics between 420 and 620 nm and a long-lived component, might indicate the involvement of lower triplet states.
Chemical Physics Letters, 2001
The photodissociation dynamics of iodo-, bromo-and chlorobenzene upon excitation at 266 nm have b... more The photodissociation dynamics of iodo-, bromo-and chlorobenzene upon excitation at 266 nm have been studied by femtosecond pump-probe spectroscopy combined with time-of-¯ight (TOF) mass spectrometric detection. The kinetics are characterized by a single time constant for chlorobenzene (1 ns) and bromobenzene (28 ps), and by two time constants for iodobenzene (700 and 350 fs). The time constant of 350 fs is due to direct dissociation. The increase of the other time constants with decreasing halogen mass supports the assignment of these constants to the decay of the initially excited p; p à states to the repulsive triplet n; r à state due to spin±orbit coupling. Ó
Femtochemistry and Femtobiology: Ultrafast Events in Molecular Science, 2004
Conference Digest. 2000 International Quantum Electronics Conference (Cat. No.00TH8504)
Summary form only given. Much effort has been put into understanding the photodissociation dynami... more Summary form only given. Much effort has been put into understanding the photodissociation dynamics of dihalomethanes in the gas phase. In solution, the task is even more challenging since supplementary processes can be present in the condensed phase; one such example is geminate recombination within the cage of solvent molecules. We present observations of the isomers for dihalomethanes, with particular
Technical Digest. 1998 EQEC. European Quantum Electronics Conference (Cat. No.98TH8326)
We present here ow new experimental and theoretical results concerning the low frequency boats in... more We present here ow new experimental and theoretical results concerning the low frequency boats in several polymnethtne dyes. Our studies show that the iduence of the solvation dynamica on the beat behavior is not reduced only to the time evolution of the chromophore spectra (the increare in beem contrast due to the haleburning eZZ is available. "-zJdFF(fi *laon where $(.) is the nuclear part of the polsrizat.ion operalor of the solvent and B(F,z) is the electric firld creat.ed by the solute inoleculc For the dipole cont.ribi~tian, VIsa = &s (e),. The fit. of the erperimerrtal date by the model developed in thts study is very good for all solvents
The Bologna process is a voluntary joint venture among 46 European countries, which has as its ob... more The Bologna process is a voluntary joint venture among 46 European countries, which has as its objective the creation of a European Higher Education Area (EHEA) by 2010. The EHEA will cover all of Europe including European Union newcomers Armenia, Azerbaijan, Georgia, Moldova, and Ukraine. Its aim is to allow for degrees and qualifications awarded in one country to be understood and recognized in other countries, thereby facilitating mobility and enhancing employability. The EHEA's overarching goals will be achieved by providing common tools and fostering cooperation in quality assurance. The common tools in the emerging EHEA, such as the European Credit Transfer and Accumulation System, Diploma supplement, a three-cycle system, and qualification frameworks, all aim to provide a system that is easy to comprehend for students, institutions, and employers.
SPIE Proceedings, 1992
We have made ultrafast time resolved pump probe measurements on the intramolecular electron trans... more We have made ultrafast time resolved pump probe measurements on the intramolecular electron transfer (ET) of the betaines, specifically betaine30 and penta-t-butyl betaine. The data have been analyzed to determine the ET rate in a range of solvent environments, at various temperatures and at a variety of pump and probe wavelengths. In all cases, the observed ET rate is fast, often faster than predicted by common ET theories. As a result, we have extended some common theories to successfully predict the measured ET rates. In addition to the ET dynamics, the data also display evidence for local heat deposition in the immediate vicinity of the betaine molecule which our extended model qualitatively predicts.
The Journal of Physical Chemistry A, 2002
ABSTRACT We studied the A-band photodissociation of bromoiodomethane, CH2BrI, in acetonitrile sol... more ABSTRACT We studied the A-band photodissociation of bromoiodomethane, CH2BrI, in acetonitrile solution at room temperature by femtosecond pump−probe spectroscopy. Initiated by the 266 nm light, this reaction leads to the CH2Br−I isomer, most likely produced via in-cage recombination of the CH2Br and I photofragments. The isomer is formed vibrationally excited with a time constant of 7.5 ps and the hottest isomer molecules are observed as early as 1 ps after the UV excitation. Vibrational relaxation of the isomer molecules takes place on two distinct time scales of a few and 40 ps. The ground-state lifetime of the isomer is about 2.5 ns.
The Journal of Chemical Physics, 1991
Reproduction in A iole or in part is permitted for any purpose of the United States Government. T... more Reproduction in A iole or in part is permitted for any purpose of the United States Government. This document has been appproved for public release and sale, its distribution is unlimited.
The Journal of Chemical Physics, 1992
The inverted regime photoinduced electron transfer kinetics of betaine-30 have been investigated ... more The inverted regime photoinduced electron transfer kinetics of betaine-30 have been investigated over a broad teiaperature range, revealing very little temperature dependence.
FEBS Letters, 2000
The transient absorption anisotropy spectrum of bacteriochlorophyll a (BChl a) in pyridine was me... more The transient absorption anisotropy spectrum of bacteriochlorophyll a (BChl a) in pyridine was measured in the wavelength interval 550^850 nm, 1 ps after optical excitation with a 792-nm femtosecond light pulse. In the wavelength region of Q y absorption and stimulated emission (775^825 nm), the anisotropy was found to be close to the theoretically expected value (0.4) for a two-level system. In the wavelength region 6507 50 nm, where the transient absorption signal is dominated by excited state absorption, the anisotropy is reduced to V V0.18. Anisotropy kinetics were measured at several wavelengths and found to be constant within the time window 0^5 ps, showing that no internal dynamics of the BChl a molecule change the anisotropy on the time scale of tens of picoseconds.
… C/C OF PIS'MA V …, 1993
... SV Chekalin and VM Farztdinov , Institute of Spectroscopy, Russian Academy of Sciences, 14209... more ... SV Chekalin and VM Farztdinov , Institute of Spectroscopy, Russian Academy of Sciences, 142092 Troitsk, Moscow Oblast, Russia E. Âkesson and V. Sundström University of ... Thomas et al.10 studied the relaxation of excited carriers in а Сбо film by absorption spectroscopy. ...
Chemical Physics Letters, 2005
The energy transfer within a series of Zn-porphyrin appended dendrimers was studied by means of t... more The energy transfer within a series of Zn-porphyrin appended dendrimers was studied by means of time-resolved fluorescence anisotropy. We show that the energy transfer process between the Zn-porphyrin units in the dendrimers is limited to a maximum of four porphyrin units. At 200 K, the energy transfer process takes place on a 100-ps time scale, and can be modeled by Fö rster theory. Our results at room temperature further show that the porphyrin units are very mobile within the dendrimer, exhibiting rotational dynamics similar to that of a monomeric building block.
Chemical Physics Letters, 2006
Solvent induced optimization of energy transfer properties in a series of Zn(II)-porphyrin-append... more Solvent induced optimization of energy transfer properties in a series of Zn(II)-porphyrin-appended dendrimers has been studied by means of excitonexciton annihilation. Upon changing from a polar solvent (tetrahydrofuran) to a non-polar solvent (3-methyl-pentane), the ...
Chemical Physics Letters, 2001
The photodissociation dynamics of iodo-, bromo-and chlorobenzene upon excitation at 266 nm have b... more The photodissociation dynamics of iodo-, bromo-and chlorobenzene upon excitation at 266 nm have been studied by femtosecond pump-probe spectroscopy combined with time-of-¯ight (TOF) mass spectrometric detection. The kinetics are characterized by a single time constant for chlorobenzene (1 ns) and bromobenzene (28 ps), and by two time constants for iodobenzene (700 and 350 fs). The time constant of 350 fs is due to direct dissociation. The increase of the other time constants with decreasing halogen mass supports the assignment of these constants to the decay of the initially excited p; p à states to the repulsive triplet n; r à state due to spin±orbit coupling.
Biophysical Journal, 1995
Energy transfer within the peripheral light-harvesting antenna of the purple bacteria Rhodobacter... more Energy transfer within the peripheral light-harvesting antenna of the purple bacteria Rhodobacter sphaeroides and Rhodopseudomonas palustris was studied by one-and two-color pump-probe absorption spectroscopy with-1 00-fs tunable pulses at room temperature and at 77 K. The energy transfer from B800 to B850 occurs with a time constant of 0.7 + 0.05 ps at room temperature and 1.8 ± 0.2 ps at 77 K and is similar in both species. Anisotropy measurements suggest a limited but fast B800 <-> B800 transfer time (0.3 ps). This is analyzed as incoherent hopping of the excitation in a system of spectrally inhomogeneous antenna pigment-protein complexes, by a master equation approach. The simulations show that the measured B800 dynamics is well described as energy transfer with a characteristic average nearest-neighbor pairwise transfer time of 0.35 ps among-10 Bchl molecules in a circular arrangement, in good agreement with the recent high-resolution structure of LH2. The possible presence of fast intramolecular relaxation processes within the Bchl a molecule was investigated by measurement of time-resolved difference absorption spectra and kinetics of Bchl a in solution and in low-temperature glasses. From these measurements it is concluded that fast transients observed at room temperature are due mainly to solvation processes, whereas at 77 K predominantly slower (>10-ps) relaxation occurs.
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1986
Excitation-energy transport in the bacteriochlorophyll antenna systems of Rhodospirillum rubrum a... more Excitation-energy transport in the bacteriochlorophyll antenna systems of Rhodospirillum rubrum and Rhodobacter sphaeroides, studied by low-intensity picosecond absorption spectroscopy
Biochimica et Biophysica Acta (BBA) - Bioenergetics, 1986
The Journal of Chemical Physics, 1991
In this work we have studied the isomerization dynamics of a cyanine dye molecule in solution. Th... more In this work we have studied the isomerization dynamics of a cyanine dye molecule in solution. The viscosity and temperature dependencies of the isomerization rate have been measured in the series of n-alcohols for three different sizes of the isomerizing group. From these measurements we conclude that the shear viscosity of the solvent is not a good measure of the
Chemical Physics Letters, 1986
The photoi~me~~tion dynamics of the dyes pinacyanol, l,l'-diethyl-4,4'-cyanine and t-stilbene in ... more The photoi~me~~tion dynamics of the dyes pinacyanol, l,l'-diethyl-4,4'-cyanine and t-stilbene in n-alcohol solutions has been studied by picosecond absorption spectroscopy. The dyes are found to isomerize without any potential barrier in the excited state. The viscosity and temperature dependence of the relaxation rates of pinacyanol and t-stilbene agree with predictions of theoretical models, whereas for 1,1'-4,4'-cyanine more complex behaviour is observed and possible reasons discussed. An excitation wavelength dependence of the isomerization rate for l,l'-4,4'-cyanine was also observed; the isomerization lifetime varies by a factor 2-3 over the absorption band. Such a dependence is predicted from the theoretical models.
Chemical Physics Letters, 2003
The photodissociation of bromobenzene in solution was investigated with ultrafast transient absor... more The photodissociation of bromobenzene in solution was investigated with ultrafast transient absorption spectroscopy following excitation at 266 nm. Ab initio calculations of lower singlet and triplet states were performed in order to guide the interpretations. The main feature of the kinetics measured between 300 and 930 nm in acetonitrile is a 9 AE 1 ps decay, which we mainly assign to predissociation. Similar decays were observed in hexane, dichloromethane and tetrachloromethane at 400 and 800 nm. Other features in acetonitrile, such as complicated short-time dynamics between 420 and 620 nm and a long-lived component, might indicate the involvement of lower triplet states.
Chemical Physics Letters, 2001
The photodissociation dynamics of iodo-, bromo-and chlorobenzene upon excitation at 266 nm have b... more The photodissociation dynamics of iodo-, bromo-and chlorobenzene upon excitation at 266 nm have been studied by femtosecond pump-probe spectroscopy combined with time-of-¯ight (TOF) mass spectrometric detection. The kinetics are characterized by a single time constant for chlorobenzene (1 ns) and bromobenzene (28 ps), and by two time constants for iodobenzene (700 and 350 fs). The time constant of 350 fs is due to direct dissociation. The increase of the other time constants with decreasing halogen mass supports the assignment of these constants to the decay of the initially excited p; p à states to the repulsive triplet n; r à state due to spin±orbit coupling. Ó
Femtochemistry and Femtobiology: Ultrafast Events in Molecular Science, 2004