TY  - JOUR
A1  - Wolf, Thomas J. A.
A1  - Holzmeier, Fabian
A1  - Wagner, Isabella
A1  - Berrah, Nora
A1  - Bostedt, Christoph
A1  - Bozek, John
A1  - Bucksbaum, Phil
A1  - Coffee, Ryan
A1  - Cryan, James
A1  - Farrell, Joe
A1  - Feifel, Raimund
A1  - Martinez, Todd J.
A1  - McFarland, Brian
A1  - Mucke, Melanie
A1  - Nandi, Saikat
A1  - Tarantelli, Francesco
A1  - Fischer, Ingo
A1  - Gühr, Markus
T1  - Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra
JF  - Applied sciences
N2  - Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a femtosecond time-resolved Auger electron spectroscopy study concerning the photofragmentation dynamics of thymine. We observe the appearance of clearly distinguishable signatures from thymines neutral photofragment isocyanic acid. Furthermore, we observe a time-dependent shift of its spectrum, which we can attribute to the influence of the charged fragment on the Auger electron. This allows us to map our time-dependent dataset onto the fragmentation coordinate. The time dependence of the shift supports efficient transformation of the excess energy gained from photoionization into kinetic energy of the fragments. Our method is broadly applicable to the investigation of photofragmentation processes.
KW  - ultrafast dynamics
KW  - Auger electron spectroscopy
KW  - photofragmentation
KW  - photochemistry
Y1  - 2017
U6  - https://doi.org/10.3390/app7070681
SN  - 2076-3417
VL  - 7
IS  - 7
PB  - MDPI
CY  - Basel
ER  - 
TY  - JOUR
A1  - Wolf, Thomas J. A.
A1  - Holzmeier, Fabian
A1  - Wagner, Isabella
A1  - Berrah, Nora
A1  - Bostedt, Christoph
A1  - Bozek, John
A1  - Bucksbaum, Philip H.
A1  - Coffee, Ryan
A1  - Cryan, James
A1  - Farrell, Joe
A1  - Feifel, Raimund
A1  - Martinez, Todd J.
A1  - McFarland, Brian
A1  - Mucke, Melanie
A1  - Nandi, Saikat
A1  - Tarantelli, Francesco
A1  - Fischer, Ingo
A1  - Gühr, Markus
T1  - Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra
JF  - Applied Sciences
N2  - Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a femtosecond time-resolved Auger electron spectroscopy study concerning the photofragmentation dynamics of thymine. We observe the appearance of clearly distinguishable signatures from thymine′s neutral photofragment isocyanic acid. Furthermore, we observe a time-dependent shift of its spectrum, which we can attribute to the influence of the charged fragment on the Auger electron. This allows us to map our time-dependent dataset onto the fragmentation coordinate. The time dependence of the shift supports efficient transformation of the excess energy gained from photoionization into kinetic energy of the fragments. Our method is broadly applicable to the investigation of photofragmentation processes.
KW  - ultrafast dynamics
KW  - Auger electron spectroscopy
KW  - photofragmentation
KW  - photochemistry
Y1  - 2017
U6  - https://doi.org/10.3390/app7070681
SN  - 2076-3417
VL  - 7
IS  - 7
PB  - MDPI
CY  - Basel
ER  - 
TY  - GEN
A1  - Wolf, Thomas J. A.
A1  - Holzmeier, Fabian
A1  - Wagner, Isabella
A1  - Berrah, Nora
A1  - Bostedt, Christoph
A1  - Bozek, John
A1  - Bucksbaum, Philip H.
A1  - Coffee, Ryan
A1  - Cryan, James
A1  - Farrell, Joe
A1  - Feifel, Raimund
A1  - Martinez, Todd J.
A1  - McFarland, Brian
A1  - Mucke, Melanie
A1  - Nandi, Saikat
A1  - Tarantelli, Francesco
A1  - Fischer, Ingo
A1  - Gühr, Markus
T1  - Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra
N2  - Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a femtosecond time-resolved Auger electron spectroscopy study concerning the photofragmentation dynamics of thymine. We observe the appearance of clearly distinguishable signatures from thymine′s neutral photofragment isocyanic acid. Furthermore, we observe a time-dependent shift of its spectrum, which we can attribute to the influence of the charged fragment on the Auger electron. This allows us to map our time-dependent dataset onto the fragmentation coordinate. The time dependence of the shift supports efficient transformation of the excess energy gained from photoionization into kinetic energy of the fragments. Our method is broadly applicable to the investigation of photofragmentation processes.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 386 
KW  - Auger electron spectroscopy
KW  - photochemistry
KW  - photofragmentation
KW  - ultrafast dynamics
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-402692
ER  - 
TY  - JOUR
A1  - Yang, Jie
A1  - Zhu, Xiaolei
A1  - Wolf, Thomas J. A.
A1  - Li, Zheng
A1  - Nunes, João Pedro Figueira
A1  - Coffee, Ryan
A1  - Cryan, James P.
A1  - Gühr, Markus
A1  - Hegazy, Kareem
A1  - Heinz, Tony F.
A1  - Jobe, Keith
A1  - Li, Renkai
A1  - Shen, Xiaozhe
A1  - Veccione, Theodore
A1  - Weathersby, Stephen
A1  - Wilkin, Kyle J.
A1  - Yoneda, Charles
A1  - Zheng, Qiang
A1  - Martinez, Todd J.
A1  - Centurion, Martin
A1  - Wang, Xijie
T1  - Imaging CF3I conical intersection and photodissociation dynamics with ultrafast electron diffraction
JF  - Science
N2  - Conical intersections play a critical role in excited-state dynamics of polyatomic molecules because they govern the reaction pathways of many nonadiabatic processes. However, ultrafast probes have lacked sufficient spatial resolution to image wave-packet trajectories through these intersections directly. Here, we present the simultaneous experimental characterization of one-photon and two-photon excitation channels in isolated CF3I molecules using ultrafast gas-phase electron diffraction. In the two-photon channel, we have mapped out the real-space trajectories of a coherent nuclear wave packet, which bifurcates onto two potential energy surfaces when passing through a conical intersection. In the one-photon channel, we have resolved excitation of both the umbrella and the breathing vibrational modes in the CF3 fragment in multiple nuclear dimensions. These findings benchmark and validate ab initio nonadiabatic dynamics calculations.
Y1  - 2018
U6  - https://doi.org/10.1126/science.aat0049
SN  - 0036-8075
SN  - 1095-9203
VL  - 361
IS  - 6397
SP  - 64
EP  - 67
PB  - American Assoc. for the Advancement of Science
CY  - Washington
ER  - 
TY  - JOUR
A1  - Wilkin, Kyle J.
A1  - Parrish, Robert M.
A1  - Yang, Jie
A1  - Wolf, Thomas J. A.
A1  - Nunes, J. Pedro F.
A1  - Gühr, Markus
A1  - Li, Renkai
A1  - Shen, Xiaozhe
A1  - Zheng, Qiang
A1  - Wang, Xijie
A1  - Martinez, Todd J.
A1  - Centurion, Martin
T1  - Diffractive imaging of dissociation and ground-state dynamics in a complex molecule
JF  - Physical review : A, Atomic, molecular, and optical physics
N2  - We have investigated the structural dynamics in photoexcited 1,2-diiodotetrafluoroethane molecules (C2F4I2) in the gas phase experimentally using ultrafast electron diffraction and theoretically using FOMO-CASCI excited-state dynamics simulations. The molecules are excited by an ultraviolet femtosecond laser pulse to a state characterized by a transition from the iodine 5p perpendicular to orbital to a mixed 5p parallel to sigma hole and CF2 center dot antibonding orbital, which results in the cleavage of one of the carbon-iodine bonds. We have observed, with sub-Angstrom resolution, the motion of the nuclear wave packet of the dissociating iodine atom followed by coherent vibrations in the electronic ground state of the C2F4I radical. The radical reaches a stable classical (nonbridged) structure in less than 200 fs.
Y1  - 2019
U6  - https://doi.org/10.1103/PhysRevA.100.023402
SN  - 2469-9926
SN  - 2469-9934
VL  - 100
IS  - 2
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Wolf, Thomas J. A.
A1  - Parrish, Robert M.
A1  - Myhre, Rolf H.
A1  - Martinez, Todd J.
A1  - Koch, Henrik
A1  - Gühr, Markus
T1  - Observation of Ultrafast Intersystem Crossing in Thymine by Extreme Ultraviolet Time-Resolved Photoelectron Spectroscopy
JF  - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2  - We studied the photoinduced ultrafast relaxation dynamics of the nucleobase thymine using gas-phase time-resolved photoelectron spectroscopy. By employing extreme ultraviolet pulses from high harmonic generation for photoionization, we substantially extend our spectral observation window with respect to previous studies. This enables us to follow relaxation of the excited state population all the way to low-lying electronic states including the ground state. In thymine, we observe relaxation from the optically bright (1)pi pi* state of thymine to a dark (1)n pi* state within 80 +/- 30 fs. The (1)n pi* state relaxes further within 3.5 +/- 0.3 ps to a low-lying electronic state. By comparison with quantum chemical simulations, we can unambiguously assign its spectroscopic signature to the (3)pi pi* state. Hence, our study draws a comprehensive picture of the relaxation mechanism of thymine including ultrafast intersystem crossing to the triplet manifold.
Y1  - 2019
U6  - https://doi.org/10.1021/acs.jpca.9b05573
SN  - 1089-5639
SN  - 1520-5215
VL  - 123
IS  - 32
SP  - 6897
EP  - 6903
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Wolf, Thomas J. A.
A1  - Sanchez, David M.
A1  - Yang, J.
A1  - Parrish, R. M.
A1  - Nunes, J. P. F.
A1  - Centurion, M.
A1  - Coffee, R.
A1  - Cryan, J. P.
A1  - Gühr, Markus
A1  - Hegazy, Kareem
A1  - Kirrander, Adam
A1  - Li, R. K.
A1  - Ruddock, J.
A1  - Shen, Xiaozhe
A1  - Vecchione, T.
A1  - Weathersby, S. P.
A1  - Weber, Peter M.
A1  - Wilkin, K.
A1  - Yong, Haiwang
A1  - Zheng, Q.
A1  - Wang, X. J.
A1  - Minitti, Michael P.
A1  - Martinez, Todd J.
T1  - The photochemical ring-opening of 1,3-cyclohexadiene imaged by ultrafast electron diffraction
JF  - Nature chemistry
N2  - The ultrafast photoinduced ring-opening of 1,3-cyclohexadiene constitutes a textbook example of electrocyclic reactions in organic chemistry and a model for photobiological reactions in vitamin D synthesis. Although the relaxation from the photoexcited electronic state during the ring-opening has been investigated in numerous studies, the accompanying changes in atomic distance have not been resolved. Here we present a direct and unambiguous observation of the ring-opening reaction path on the femtosecond timescale and subangstrom length scale using megaelectronvolt ultrafast electron diffraction. We followed the carbon-carbon bond dissociation and the structural opening of the 1,3-cyclohexadiene ring by the direct measurement of time-dependent changes in the distribution of interatomic distances. We observed a substantial acceleration of the ring-opening motion after internal conversion to the ground state due to a steepening of the electronic potential gradient towards the product minima. The ring-opening motion transforms into rotation of the terminal ethylene groups in the photoproduct 1,3,5-hexatriene on the subpicosecond timescale.
KW  - Organic chemistry
KW  - Photochemistry
KW  - Physical chemistry
KW  - Theoretical chemistry
Y1  - 2019
U6  - https://doi.org/10.1038/s41557-019-0252-7
SN  - 1755-4330
SN  - 1755-4349
VL  - 11
IS  - 6
SP  - 504
EP  - 509
PB  - Nature Publ. Group
CY  - London
ER  -