Daniel Strasser - Academia.edu (original) (raw)
Papers by Daniel Strasser
The Journal of Chemical Physics
We study the competing mechanisms in the Coulomb explosion of 2-propanol dication, formed by an u... more We study the competing mechanisms in the Coulomb explosion of 2-propanol dication, formed by an ultrafast EUV pulse. Over 20 product channels are identified and characterized using 3D coincidence imaging of the ionic fragments. The momentum correlations in the three-body fragmentation channels provide evidence for a dominant sequential mechanism, starting with cleavage of a C-C bond, ejecting and cations, followed by a secondary fragmentation of the hydroxyethyl cation that can be delayed for up to a microsecond after ionization. C-O bond dissociation channels are less frequent, involving proton-transfer and double-proton transfer, forming and products respectively and exhibiting mixed sequential and concerted character. These results can be explained by the high potential barrier for the C-O bond dissociation seen in our ab initio quantum chemical calculations. We also observe coincident COH+ + C2Hn+ ions, suggesting exotic structural rearrangements, starting from the Frank-Condon ...
Physical Chemistry Chemical Physics
3D fragment imaging of the fluoroformate anion (FCO2−) dissociative photodetachment products show... more 3D fragment imaging of the fluoroformate anion (FCO2−) dissociative photodetachment products shows reductive fragmentation, forming FCO + O, as well as a dominant cleavage of the CF bond.
Physical chemistry chemical physics : PCCP, 2020
Dissociative photodetachment of the FCO2- fluoroformate complex by intense laser pulses is studie... more Dissociative photodetachment of the FCO2- fluoroformate complex by intense laser pulses is studied using 3D coincidence fragment imaging. The main channels are found to be CO2 + F and FCO + O. Cleavage of the C-F bond is attributed to dissociation on the B[combining tilde]2A1 excited state of the neutral FCO2 radical with significant internal excitation of the molecular fragment, while reductive dissociation of the CO2 moiety is assigned to higher lying states. The measured dissociative ionization products of double-photodetachment are discussed and attributed to intense-laser ionization of dissociative photodetachment products.
![Research paper thumbnail of Double Photodetachment of F¯∙H2O: Experimental and Theoretical Studies of [F∙H2O]+](https://attachments.academia-assets.com/79834403/thumbnails/1.jpg)
](The Journal of Physical Chemistry Letters
Double photodetachment of the cluster F‾•H 2 O in a strong laser field is explored in a combined ... more Double photodetachment of the cluster F‾•H 2 O in a strong laser field is explored in a combined experimental-theoretical study. Products are observed experimentally by coincidence photofragment imaging following double ionization by intense laser pulses. Theoretically, equation of motion coupled cluster calculations (EOM-CC), suitable for modeling strong correlation effects in the electronic wavefunction, shed light on the Franck-Condon region and ab initio molecular dynamics (AIMD) simulations also performed using EOM-CC methods reveal the fragmentation dynamics in time on the lowest lying singlet and triplet states of [F•H 2 O] +. The simulations show the formation of H 2 O + + F, which is the predominant experimentally observed product channel. Suggestions are proposed for the formation mechanisms of the minor products, e.g. the very interesting H 2 F + , which involves significant geometrical rearrangement. Analysis of the results suggests interesting future directions for the exploration of photodetachment of anionic clusters in an intense laser field.
The Journal of Physical Chemistry Letters
Despite the abundance of data concerning single-photon double ionization of methanol, the spin st... more Despite the abundance of data concerning single-photon double ionization of methanol, the spin state of the emitted electron pair has never been determined. Here we present the first evidence that identifies the emitted electron pair spin as overwhelmingly singlet when the dication forms in low-energy configurations. The experimental data show that while the yield of the CH 2 O + + H 3 + Coulomb explosion channel is abundant, the metastable methanol dication is largely absent. According to high-level ab initio simulations, these facts indicate that photoionization promptly forms singlet dication states, where they quickly decompose through various channels, with significant H 3 + yields on the low-lying states. In contrast, if we assume that the initial dication is formed in one of the low-lying triplet states, the ab initio simulations exhibit a metastable dication, contradicting the experimental findings. Comparing the average simulated branching ratios with the experimental data suggests a >3 order of magnitude enhancement of the singlet:triplet ratio compared with their respective 1:3 multiplicities.
Communications Chemistry
The time scales and formation mechanisms of tri-hydrogen cation products in organic molecule ioni... more The time scales and formation mechanisms of tri-hydrogen cation products in organic molecule ionization processes are poorly understood, despite their cardinal role in the chemistry of the interstellar medium and in other chemical systems. Using an ultrafast extreme-ultraviolet pump and time-resolved near-IR probe, combined with high-level ab initio molecular dynamics calculations, here we report unambiguously that H 3 + formation in double-ionization of methanol occurs on a sub 100 fs time scale, settling previous conflicting findings of strong-field Coulomb explosion experiments. Our combined experimentalcomputational studies suggest that ultrafast competition, between proton-transfer and longrange electron-transfer processes, determines whether the roaming neutral H 2 dynamics on the dication result in H þ 3 or H þ 2 fragments respectively.
Review of Scientific Instruments
Physical Chemistry Chemical Physics
Triatomic Coulomb explosion dynamics are initiated by single-photon double ionization of N2O with... more Triatomic Coulomb explosion dynamics are initiated by single-photon double ionization of N2O with an ultrafast EUV pulse and are probed by delayed near-IR pulses. The triatomic benchmark system exhibits competing...
EPJ Web of Conferences
We present time-resolved coincidence imaging of F2− photodissociation by 400nm and intense 800nm ... more We present time-resolved coincidence imaging of F2− photodissociation by 400nm and intense 800nm ultrafast pulses. Coincidence fragment imaging reveals parallel and perpendicular single photon dissociation on 2Σg+ and 2πg states, and additional intense-field dissociation features.
Angewandte Chemie International Edition
Review of Scientific Instruments
We present the design and simulations of a 3D coincidence imaging spectrometer for fast beam phot... more We present the design and simulations of a 3D coincidence imaging spectrometer for fast beam photofragmentation experiments. Coincidence detection of cationic, neutral, and anionic fragments involves spectrometer aberrations that are successfully corrected by an analytical model combined with exact numerical simulations. The spectrometer performance is experimentally demonstrated by characterization of four different channels of intense 800 nm pulse interaction with F − 2 : F + F photodissociation, F + F dissociative photodetachment, F + + F dissociative ionization, and F + + F + coulomb explosion. Improved measurement of F − 2 photodissociation with a 400 nm photon allows a better determination of the F − 2 anion dissociation energy, 1.256 ± 0.005 eV.
Angewandte Chemie (International ed. in English), Jan 27, 2018
In an effort to characterize the electronic states of ethylenedione, OCCO, photoelectron-photofra... more In an effort to characterize the electronic states of ethylenedione, OCCO, photoelectron-photofragment coincidence (PPC) spectroscopy was applied to measure anions at m/z 56 and 57 using a pulsed discharge of glyoxal vapor and N₂O. PPC measurements at a photon energy of 3.20 eV yield photoelectron spectra in coincidence with either neutral photofragments or stable neutral products. The measurements showed that primarily stable neutral products were formed, with photoelectron spectra consistent with the oxyallyl diradical, C₃H₄O, and acetone enolate radical, C₃H₅O. The spectra were also found to have features nearly identical to those reported for OCCO and HOCCO by Sanov and co-workers. The stability of the neutral products, as well as an examination of spectra reported for the oxyallyl anion and acetone enolate show that the previous assignments of OCCO and HOCCO are in error, and are instead attributed here to the oxyallyl diradical, C₃H₄O, and the acetone enolate radical, C₃H₅O.
Physical chemistry chemical physics : PCCP, Jan 31, 2017
Single-photon Coulomb explosion of methanol is instigated using the broad bandwidth pulse achieve... more Single-photon Coulomb explosion of methanol is instigated using the broad bandwidth pulse achieved through high-order harmonics generation. Using 3D coincidence fragment imaging of one molecule at a time, the kinetic energy release (KER) and angular distributions of the products are measured in different Coulomb explosion (CE) channels. Two-body CE channels breaking either the C-O or the C-H bonds are described as well as a proton migration channel forming H2O(+), which is shown to exhibit higher KER. The results are compared to intense-field Coulomb explosion measurements in the literature. The interpretation of broad bandwidth single-photon CE data is discussed and supported by ab initio calculations of the predominant C-O bond breaking CE channel. We discuss the importance of these findings for achieving time resolved imaging of ultrafast dynamics.
Journal of Instrumentation
A simple mass selection technique which allows one to clean a keV ion beam of undesirable masses ... more A simple mass selection technique which allows one to clean a keV ion beam of undesirable masses while stored in an Electrostatic Ion Beam Trap (EIBT) is described. The technique is based on the time-of-flight principle and takes advantage of the long storage times and self-bunching that are possible in this type of traps (self bunching being the effect that
The journal of physical chemistry. A, Jan 27, 2017
The competition of intense-field multiple-detachment with efficient photodissociation of F2¯ is s... more The competition of intense-field multiple-detachment with efficient photodissociation of F2¯ is studied as a function of laser peak intensity. The main product channels are disentangled and characterized by 3D coincidence fragment imaging. The presented kinetic energy release spectra, angular distributions, as well as two-color pump-probe measurements allow identification of competing sequential and nonsequential mechanisms. Dissociative detachment, producing two neutral atoms (F + F), is found to be dominated by a sequential mechanism of photodissociation (F¯ + F), followed by detachment of the atomic anion fragment. In contrast, dissociative ionization (F + F(+)) shows competing contributions of both a sequential two-step mechanism as well as a nonsequential double-detachment of the molecular anion, which are distinguished by the kinetic energy released in the dissociation. Triple-detachment is found to be nonsequential in nature and results in Coulomb explosion (F(+) + F(+)). Fur...
Experimental Eye Research, Jan 31, 2007
The pineal gland of the zebrafish (Danio rerio) is a clock-containing photoreceptive organ. Super... more The pineal gland of the zebrafish (Danio rerio) is a clock-containing photoreceptive organ. Superfused pineal glands kept in darkness display rhythmic melatonin production that lasts for days, with high melatonin levels during the night and low levels during the day. Nocturnal light, however, evokes an acute suppression of melatonin synthesis in the photoreceptor cells. Towards characterizing zebrafish pineal photopigment that is involved in the acute melatonin suppression we have measured the spectral sensitivity of melatonin-suppression response in superfused pineal glands. The effect of 2 h light exposure of seven wavelengths (l avg 408, 460, 512, 560, 608, 660 and 697 AE 10e15 nm) at multiple irradiances (10 7 e10 14 photons/cm 2 /s) was determined, and an action spectrum was plotted. The resultant action spectrum provides evidence for the involvement of multiple photopigments in melatonin suppression. The most efficient melatonin-suppression response was achieved by exposure to light of around 512 nm; however, another peak of lower irradiance sensitivity was observed in the middle to long wavelengths. Opsins-specific RT-PCR analysis confirmed the expression of exo-rhodopsin and visual red-sensitive opsin in the pineal gland, while other zebrafish visual opsins as well as VA and VAL opsins were not detected. Dartnall monograms for exo-rhodopsin and visual red-sensitive opsin account for most but not all of the spectral sensitivity features. Therefore, additional pineal photopigments may contribute to the melatonin-suppression response in the pineal gland.
The Journal of Chemical Physics
We study the competing mechanisms in the Coulomb explosion of 2-propanol dication, formed by an u... more We study the competing mechanisms in the Coulomb explosion of 2-propanol dication, formed by an ultrafast EUV pulse. Over 20 product channels are identified and characterized using 3D coincidence imaging of the ionic fragments. The momentum correlations in the three-body fragmentation channels provide evidence for a dominant sequential mechanism, starting with cleavage of a C-C bond, ejecting and cations, followed by a secondary fragmentation of the hydroxyethyl cation that can be delayed for up to a microsecond after ionization. C-O bond dissociation channels are less frequent, involving proton-transfer and double-proton transfer, forming and products respectively and exhibiting mixed sequential and concerted character. These results can be explained by the high potential barrier for the C-O bond dissociation seen in our ab initio quantum chemical calculations. We also observe coincident COH+ + C2Hn+ ions, suggesting exotic structural rearrangements, starting from the Frank-Condon ...
Physical Chemistry Chemical Physics
3D fragment imaging of the fluoroformate anion (FCO2−) dissociative photodetachment products show... more 3D fragment imaging of the fluoroformate anion (FCO2−) dissociative photodetachment products shows reductive fragmentation, forming FCO + O, as well as a dominant cleavage of the CF bond.
Physical chemistry chemical physics : PCCP, 2020
Dissociative photodetachment of the FCO2- fluoroformate complex by intense laser pulses is studie... more Dissociative photodetachment of the FCO2- fluoroformate complex by intense laser pulses is studied using 3D coincidence fragment imaging. The main channels are found to be CO2 + F and FCO + O. Cleavage of the C-F bond is attributed to dissociation on the B[combining tilde]2A1 excited state of the neutral FCO2 radical with significant internal excitation of the molecular fragment, while reductive dissociation of the CO2 moiety is assigned to higher lying states. The measured dissociative ionization products of double-photodetachment are discussed and attributed to intense-laser ionization of dissociative photodetachment products.
The Journal of Physical Chemistry Letters
Double photodetachment of the cluster F‾•H 2 O in a strong laser field is explored in a combined ... more Double photodetachment of the cluster F‾•H 2 O in a strong laser field is explored in a combined experimental-theoretical study. Products are observed experimentally by coincidence photofragment imaging following double ionization by intense laser pulses. Theoretically, equation of motion coupled cluster calculations (EOM-CC), suitable for modeling strong correlation effects in the electronic wavefunction, shed light on the Franck-Condon region and ab initio molecular dynamics (AIMD) simulations also performed using EOM-CC methods reveal the fragmentation dynamics in time on the lowest lying singlet and triplet states of [F•H 2 O] +. The simulations show the formation of H 2 O + + F, which is the predominant experimentally observed product channel. Suggestions are proposed for the formation mechanisms of the minor products, e.g. the very interesting H 2 F + , which involves significant geometrical rearrangement. Analysis of the results suggests interesting future directions for the exploration of photodetachment of anionic clusters in an intense laser field.
The Journal of Physical Chemistry Letters
Despite the abundance of data concerning single-photon double ionization of methanol, the spin st... more Despite the abundance of data concerning single-photon double ionization of methanol, the spin state of the emitted electron pair has never been determined. Here we present the first evidence that identifies the emitted electron pair spin as overwhelmingly singlet when the dication forms in low-energy configurations. The experimental data show that while the yield of the CH 2 O + + H 3 + Coulomb explosion channel is abundant, the metastable methanol dication is largely absent. According to high-level ab initio simulations, these facts indicate that photoionization promptly forms singlet dication states, where they quickly decompose through various channels, with significant H 3 + yields on the low-lying states. In contrast, if we assume that the initial dication is formed in one of the low-lying triplet states, the ab initio simulations exhibit a metastable dication, contradicting the experimental findings. Comparing the average simulated branching ratios with the experimental data suggests a >3 order of magnitude enhancement of the singlet:triplet ratio compared with their respective 1:3 multiplicities.
Communications Chemistry
The time scales and formation mechanisms of tri-hydrogen cation products in organic molecule ioni... more The time scales and formation mechanisms of tri-hydrogen cation products in organic molecule ionization processes are poorly understood, despite their cardinal role in the chemistry of the interstellar medium and in other chemical systems. Using an ultrafast extreme-ultraviolet pump and time-resolved near-IR probe, combined with high-level ab initio molecular dynamics calculations, here we report unambiguously that H 3 + formation in double-ionization of methanol occurs on a sub 100 fs time scale, settling previous conflicting findings of strong-field Coulomb explosion experiments. Our combined experimentalcomputational studies suggest that ultrafast competition, between proton-transfer and longrange electron-transfer processes, determines whether the roaming neutral H 2 dynamics on the dication result in H þ 3 or H þ 2 fragments respectively.
Review of Scientific Instruments
Physical Chemistry Chemical Physics
Triatomic Coulomb explosion dynamics are initiated by single-photon double ionization of N2O with... more Triatomic Coulomb explosion dynamics are initiated by single-photon double ionization of N2O with an ultrafast EUV pulse and are probed by delayed near-IR pulses. The triatomic benchmark system exhibits competing...
EPJ Web of Conferences
We present time-resolved coincidence imaging of F2− photodissociation by 400nm and intense 800nm ... more We present time-resolved coincidence imaging of F2− photodissociation by 400nm and intense 800nm ultrafast pulses. Coincidence fragment imaging reveals parallel and perpendicular single photon dissociation on 2Σg+ and 2πg states, and additional intense-field dissociation features.
Angewandte Chemie International Edition
Review of Scientific Instruments
We present the design and simulations of a 3D coincidence imaging spectrometer for fast beam phot... more We present the design and simulations of a 3D coincidence imaging spectrometer for fast beam photofragmentation experiments. Coincidence detection of cationic, neutral, and anionic fragments involves spectrometer aberrations that are successfully corrected by an analytical model combined with exact numerical simulations. The spectrometer performance is experimentally demonstrated by characterization of four different channels of intense 800 nm pulse interaction with F − 2 : F + F photodissociation, F + F dissociative photodetachment, F + + F dissociative ionization, and F + + F + coulomb explosion. Improved measurement of F − 2 photodissociation with a 400 nm photon allows a better determination of the F − 2 anion dissociation energy, 1.256 ± 0.005 eV.
Angewandte Chemie (International ed. in English), Jan 27, 2018
In an effort to characterize the electronic states of ethylenedione, OCCO, photoelectron-photofra... more In an effort to characterize the electronic states of ethylenedione, OCCO, photoelectron-photofragment coincidence (PPC) spectroscopy was applied to measure anions at m/z 56 and 57 using a pulsed discharge of glyoxal vapor and N₂O. PPC measurements at a photon energy of 3.20 eV yield photoelectron spectra in coincidence with either neutral photofragments or stable neutral products. The measurements showed that primarily stable neutral products were formed, with photoelectron spectra consistent with the oxyallyl diradical, C₃H₄O, and acetone enolate radical, C₃H₅O. The spectra were also found to have features nearly identical to those reported for OCCO and HOCCO by Sanov and co-workers. The stability of the neutral products, as well as an examination of spectra reported for the oxyallyl anion and acetone enolate show that the previous assignments of OCCO and HOCCO are in error, and are instead attributed here to the oxyallyl diradical, C₃H₄O, and the acetone enolate radical, C₃H₅O.
Physical chemistry chemical physics : PCCP, Jan 31, 2017
Single-photon Coulomb explosion of methanol is instigated using the broad bandwidth pulse achieve... more Single-photon Coulomb explosion of methanol is instigated using the broad bandwidth pulse achieved through high-order harmonics generation. Using 3D coincidence fragment imaging of one molecule at a time, the kinetic energy release (KER) and angular distributions of the products are measured in different Coulomb explosion (CE) channels. Two-body CE channels breaking either the C-O or the C-H bonds are described as well as a proton migration channel forming H2O(+), which is shown to exhibit higher KER. The results are compared to intense-field Coulomb explosion measurements in the literature. The interpretation of broad bandwidth single-photon CE data is discussed and supported by ab initio calculations of the predominant C-O bond breaking CE channel. We discuss the importance of these findings for achieving time resolved imaging of ultrafast dynamics.
Journal of Instrumentation
A simple mass selection technique which allows one to clean a keV ion beam of undesirable masses ... more A simple mass selection technique which allows one to clean a keV ion beam of undesirable masses while stored in an Electrostatic Ion Beam Trap (EIBT) is described. The technique is based on the time-of-flight principle and takes advantage of the long storage times and self-bunching that are possible in this type of traps (self bunching being the effect that
The journal of physical chemistry. A, Jan 27, 2017
The competition of intense-field multiple-detachment with efficient photodissociation of F2¯ is s... more The competition of intense-field multiple-detachment with efficient photodissociation of F2¯ is studied as a function of laser peak intensity. The main product channels are disentangled and characterized by 3D coincidence fragment imaging. The presented kinetic energy release spectra, angular distributions, as well as two-color pump-probe measurements allow identification of competing sequential and nonsequential mechanisms. Dissociative detachment, producing two neutral atoms (F + F), is found to be dominated by a sequential mechanism of photodissociation (F¯ + F), followed by detachment of the atomic anion fragment. In contrast, dissociative ionization (F + F(+)) shows competing contributions of both a sequential two-step mechanism as well as a nonsequential double-detachment of the molecular anion, which are distinguished by the kinetic energy released in the dissociation. Triple-detachment is found to be nonsequential in nature and results in Coulomb explosion (F(+) + F(+)). Fur...
Experimental Eye Research, Jan 31, 2007
The pineal gland of the zebrafish (Danio rerio) is a clock-containing photoreceptive organ. Super... more The pineal gland of the zebrafish (Danio rerio) is a clock-containing photoreceptive organ. Superfused pineal glands kept in darkness display rhythmic melatonin production that lasts for days, with high melatonin levels during the night and low levels during the day. Nocturnal light, however, evokes an acute suppression of melatonin synthesis in the photoreceptor cells. Towards characterizing zebrafish pineal photopigment that is involved in the acute melatonin suppression we have measured the spectral sensitivity of melatonin-suppression response in superfused pineal glands. The effect of 2 h light exposure of seven wavelengths (l avg 408, 460, 512, 560, 608, 660 and 697 AE 10e15 nm) at multiple irradiances (10 7 e10 14 photons/cm 2 /s) was determined, and an action spectrum was plotted. The resultant action spectrum provides evidence for the involvement of multiple photopigments in melatonin suppression. The most efficient melatonin-suppression response was achieved by exposure to light of around 512 nm; however, another peak of lower irradiance sensitivity was observed in the middle to long wavelengths. Opsins-specific RT-PCR analysis confirmed the expression of exo-rhodopsin and visual red-sensitive opsin in the pineal gland, while other zebrafish visual opsins as well as VA and VAL opsins were not detected. Dartnall monograms for exo-rhodopsin and visual red-sensitive opsin account for most but not all of the spectral sensitivity features. Therefore, additional pineal photopigments may contribute to the melatonin-suppression response in the pineal gland.