Shunsuke Adachi

Direct Observation of Ground-State Product Formation in a 1,3-Cyclohexadiene Ring-Opening Reaction

Ultrafast photoelectron imaging using a 90 nm vacuum-UV probe pulse is applied to the ring-opening reaction of 1,3-cyclohexadiene (CHD) in the gas phase, and formation of 1,3,5-hexatriene (HT) and CHD in their electronic ground states is observed in real time. The analysis of the transient photoelectron kinetic energy spectra reveals the branching ratio into HT and CHD as 3:7 upon 270 nm photoexcitation. The ratio is in reasonable agreement with the experimental values reported for the liquid phase and theoretical values for the gas phase, resolving the discrepancy.

Generation of intense single-order harmonic pulse in the vacuum ultraviolet region using a deep ultraviolet driving laser

A 90 nm single-order harmonic pulse with a 200 nJ on-target pulse energy at 1 kHz was realized through a harmonic generation process with a 35 fs Ti:Sa third harmonic in a Kr gas cell.

Wavelength Dependence of UV Photoemission from Solvated Electrons in Bulk Water, Methanol, and Ethanol

We have measured the wavelength dependence (340-215 nm) of one-photon photoemission from the ground electronic state of solvated electrons in bulk water, methanol, and ethanol. In every case, the vertical electron binding energy (VBE) gradually increased with photon energy, indicating that the photoelectron kinetic energy diminishes as a result of electron-vibration inelastic scattering prior to emission from the liquid surface. In contrast, the VBE of the Rydberg electron in DABCO (1,4-diazabicyclo[2,2,2]octane), which has a surface-excess density, revealed no clear wavelength dependence. These results suggest that the solvated electrons are created predominantly in the bulk and that VBEs measured using UV photoemission spectroscopy of liquids generally require energy corrections to account for inelastic scattering effects. From the wavelength dependence, we have re-estimated the VBEs of solvated electrons in bulk water, methanol, and ethanol to be 3.3, 3.1, and 3.1 eV, respectively. Hydrated electrons were also identified by photoemission spectroscopy using 90 nm radiation.

Photoisomerization of Vibrationally Hot Tetramethylethylene Produced by Ultrafast Internal Conversion from the Excited State

Isomerization of tetramethylethylene (TME) following ultrafast internal conversion was investigated using time-resolved photoelectron spectroscopy with vacuum-ultraviolet probe pulses. The difference photoelectron spectrum at τ = 15 ps was reasonably well reproduced using a linear combination of static photoelectron spectra of TME and its isomers. The isomers were produced as a consequence of unimolecular reaction of vibrationally hot TME, created by internal conversion from the excited state.

Pump–probe photoelectron spectroscopy by a high-power 90 nm vacuum-ultraviolet laser

We present pump–probe photoelectron spectroscopy of Kr and NO using a high-power vacuum-ultraviolet (VUV) laser at a wavelength of 90 nm. Clear quantum beats are observed in the photoelectron angular distributions as well as in the photoelectron yields, resulting from the coherent excitation of two Kr Rydberg states by the VUV pump. The entire Franck–Condon envelope of the NO A(2Σ+) excited state is also successfully captured by the VUV probe.

Intense vacuum-ultraviolet single-order harmonic pulse by a deep-ultraviolet driving laser

A 90-nm single-order harmonic pulse with a 100-nJ pulse energy was realized by the frequency-tripling of 35-fs Ti:Sa third harmonic in a krypton gas cell.