Intervalley scattering in MoS2 imaged by two-photon photoemission with a high-harmonic probe

Ultrafast table-top x-ray spectroscopy <a>at the carbon K-edge </a>is used to measure the x-ray spectral features of benzene <a>radical cations (Bz+). The ground state of the cation is prepared selectively by </a><a>two-photon ionization of neutral benzene, and the x-ray spectra are probed at early times after the ionization by transient absorption using x-rays produced by high harmonic generation (HHG). </a><a>Bz+ is well known to undergo Jahn-Teller </a>distortion, leading to a lower symmetry and splitting of the π orbitals. Comparison of the x-ray absorption spectra of the neutral and the cation reveals a splitting of the two degenerate π* orbitals as well as an appearance of a new peak due to excitation to the partially occupied π -subshell. The <a>π*</a> orbital splitting of the cation, elucidated on the basis of high-level calculations in a companion theoretical paper [Vidal et al, submitted to J. Phys. Chem. Lett.; ChemRxiv link: doi XXXXX], is discovered to be due to both the symmetry distortion and even more dominant spin coupling of the unpaired electron in the partially vacant π orbital (from ionization) with the unpaired electrons resulting from the transition from the 1sC core orbital to the fully vacant <a>π* </a>orbitals.

Download Full-text

Table-Top X-ray Spectroscopy of Benzene Radical Cation

10.26434/chemrxiv.12798734.v1 ◽

2020 ◽

Author(s):

Michael Epshtein ◽

Valeriu Scutelnic ◽

Zheyue Yang ◽

Tian Xue ◽

Marta L. Vidal ◽

...

Keyword(s):

Transient Absorption ◽

High Harmonic ◽

Radical Cations ◽

Spin Coupling ◽

X Rays ◽

X Ray ◽

Two Photon ◽

Jahn Teller ◽

Theoretical Paper ◽

High Level

Ultrafast table-top x-ray spectroscopy <a>at the carbon K-edge </a>is used to measure the x-ray spectral features of benzene <a>radical cations (Bz+). The ground state of the cation is prepared selectively by </a><a>two-photon ionization of neutral benzene, and the x-ray spectra are probed at early times after the ionization by transient absorption using x-rays produced by high harmonic generation (HHG). </a><a>Bz+ is well known to undergo Jahn-Teller </a>distortion, leading to a lower symmetry and splitting of the π orbitals. Comparison of the x-ray absorption spectra of the neutral and the cation reveals a splitting of the two degenerate π* orbitals as well as an appearance of a new peak due to excitation to the partially occupied π -subshell. The <a>π*</a> orbital splitting of the cation, elucidated on the basis of high-level calculations in a companion theoretical paper [Vidal et al, submitted to J. Phys. Chem. Lett.; ChemRxiv link: doi XXXXX], is discovered to be due to both the symmetry distortion and even more dominant spin coupling of the unpaired electron in the partially vacant π orbital (from ionization) with the unpaired electrons resulting from the transition from the 1sC core orbital to the fully vacant <a>π* </a>orbitals.

Download Full-text

Two-photon resonant excitation of a doubly excited state in He atoms by high-harmonic pulses

Optics Express ◽

10.1364/oe.16.021922 ◽

2008 ◽

Vol 16 (26) ◽

pp. 21922 ◽

Cited By ~ 21

Author(s):

Taro Sekikawa ◽

Tatsuya Okamoto ◽

Eisuke Haraguchi ◽

Mikio Yamashita ◽

Takashi Nakajima

Keyword(s):

Excited State ◽

High Harmonic ◽

Resonant Excitation ◽

Two Photon ◽

Doubly Excited

Download Full-text

Time-resolved high-harmonic spectroscopy of ultrafast ring-opening of 1,3-cyclohexadiene

EPJ Web of Conferences ◽

10.1051/epjconf/201920509017 ◽

2019 ◽

Vol 205 ◽

pp. 09017

Author(s):

Keisuke Kaneshima ◽

Yuki Ninota ◽

Taro Sekikawa

Keyword(s):

Ring Opening ◽

High Harmonic ◽

Harmonic Signal ◽

Photochemical Reactions ◽

Photon Absorption ◽

Nuclear Dynamics ◽

Time Resolved ◽

Two Photon Absorption ◽

Two Photon ◽

Bond Rearrangement

We report, to the best of our knowledge, the first time-resolved high-harmonic spectroscopy (TR-HHS) study of a chemical bond rearrangement. We investigate the transient change of the high-harmonic signal from 1,3-cyclohexadiene (CHD), which undergoes ring-opening and isomerizes to 1,3,5-hexatriene (HT) upon photoexcitation. By associating the variation in the harmonic yield to the changes in the electronic state and vibrational frequencies of the molecule due to isomerization, we find that the CHD excited via two-photon absorption of 3.1 eV photons isomerizes to HT, i.e., ring-opening occurs, around 400 fs after the excitation. The present results demonstrate that TR-HHS, which can track both electronic and nuclear dynamics, is a powerful tool for studying ultrafast photochemical reactions.

Download Full-text

Two-photon excitation microscopy in cellular biophysics

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100136684 ◽

1995 ◽

Vol 53 ◽

pp. 62-63

Author(s):

David W. Piston ◽

Brian D. Bennett ◽

Robert G. Summers

Keyword(s):

Confocal Microscopy ◽

Laser Beam ◽

Duty Cycle ◽

Excited Electronic State ◽

Input Power ◽

Two Photon ◽

Simultaneous Absorption ◽

Photon Excitation ◽

Very High ◽

Two Photon Excitation

Two-photon excitation microscopy (TPEM) provides attractive advantages over confocal microscopy for three-dimensionally resolved fluorescence imaging and photochemistry. Two-photon excitation arises from the simultaneous absorption of two photons in a single quantitized event whose probability is proportional to the square of the instantaneous intensity. For example, two red photons can cause the transition to an excited electronic state normally reached by absorption in the ultraviolet. In practice, two-photon excitation is made possible by the very high local instantaneous intensity provided by a combination of diffraction-limited focusing of a single laser beam in the microscope and the temporal concentration of 100 femtosecond pulses generated by a mode-locked laser. Resultant peak excitation intensities are 106 times greater than the CW intensities used in confocal microscopy, but the pulse duty cycle of 10-5 maintains the average input power on the order of 10 mW, only slightly greater than the power normally used in confocal microscopy.

Download Full-text

Two-photon excitation fluorescence microscopy in living systems

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100146618 ◽

1993 ◽

Vol 51 ◽

pp. 154-155 ◽

Cited By ~ 1

Author(s):

David W. Piston

Keyword(s):

Confocal Microscopy ◽

Fluorescence Microscopy ◽

Singlet State ◽

Excited Electronic State ◽

Input Power ◽

Two Photon ◽

Simultaneous Absorption ◽

Photon Excitation ◽

Very High ◽

Two Photon Excitation

Two-photon excitation fluorescence microscopy provides attractive advantages over confocal microscopy for three-dimensionally resolved fluorescence imaging. Two-photon excitation arises from the simultaneous absorption of two photons in a single quantitized event whose probability is proportional to the square of the instantaneous intensity. For example, two red photons can cause the transition to an excited electronic state normally reached by absorption in the ultraviolet. In our fluorescence experiments, the final excited state is the same singlet state that is populated during a conventional fluorescence experiment. Thus, the fluorophore exhibits the same emission properties (e.g. wavelength shifts, environmental sensitivity) used in typical biological microscopy studies. In practice, two-photon excitation is made possible by the very high local instantaneous intensity provided by a combination of diffraction-limited focusing of a single laser beam in the microscope and the temporal concentration of 100 femtosecond pulses generated by a mode-locked laser. Resultant peak excitation intensities are 106 times greater than the CW intensities used in confocal microscopy, but the pulse duty cycle of 10−5 maintains the average input power on the order of 10 mW, only slightly greater than the power normally used in confocal microscopy.

Download Full-text