Photoelectron Imaging Signature for Selective Formation of Icosahedral Anionic Silver Cages Encapsulating Group 5 Elements: M@Ag12- (M = V, Nb, and Ta).

An assembly of 13 atoms can form highly symmetric architectures like those belonging to D3h, Oh, D5h, and Ih point groups. Here, using photoelectron imaging spectroscopy in combination with density functional theory (DFT) calculations, we present a simple yet convincing experimental signature for the selective formation of icosahedral cages of anionic silver clusters encapsulating a dopant atom of group 5 elements: M@Ag12- (M = V, Nb, and Ta). Their photoelectron images obtained at 4 eV closely resemble one another: only a single ring is observed, which is assignable to photodetachment signals from a 5-fold degenerate superatomic 1D electronic shell in the 1S21P61D10 configuration of valence electrons. The perfect degeneracy represents an unambiguous fingerprint of an icosahedral symmetry, which would otherwise be lifted in all of the other structural isomers. DFT calculations confirm that Ih forms are the most stable and that D5h, Oh, and D3h structures are not found even in metastable states.

Photodestruction Action Spectroscopy of Silver Cluster Anions, AgN- (N = 3-19), with a Linear Ion Trap: Observation of Bound Excited States above the Photodetachment Threshold.

Electron detachment thresholds of metal cluster anions, MN-, are a few electron volts. The excess electron is therefore detached by visible or ultraviolet light, which also creates low-lying bound electronic states, MN-*; i.e., MN-* energetically overlaps with the continuum, MN + e-. Here, we perform action spectroscopy of photodestruction, leading either to photodetachment or to photofragmentation, for size-selected silver cluster anions, AgN- (N = 3-19), to unveil such bound electronic states embedded in the continuum. The experiment takes advantage of a linear ion trap that enables us to measure photodestruction spectra with high quality at well-defined temperatures, where bound excited states, AgN-*, are clearly identified above their vertical detachment energies. Structural optimization of AgN- (N = 3-19) is conducted by using density functional theory (DFT), which is followed by calculations of vertical excitation energies by time-dependent DFT to assign the observed bound states. Spectral evolution observed as a function of cluster size is also discussed, where the optimized geometries are found to be closely related to the observed spectral profiles. A plasmonic band consisting of nearly degenerate individual excitations is observed for N = 19.

Photoelectron imaging of size-selected metal cluster anions in a quasi-continuous mode.

We present a novel high-repetition-rate photoelectron imaging (PEI) apparatus for exploring electronic structures of metal cluster anions. A continuous beam of mass-selected metal cluster anions, generated by a magnetron-sputtering cluster-ion source coupled with a quadrupole mass filter, is chopped into sub-megahertz ion bunches using a high-voltage pulser. The quasi-continuous anion beam is introduced into a PEI spectrometer, where the anions are photodetached using a 404 nm (3.07 eV) continuous-wave laser diode. As a demonstration, we acquire photoelectron images for size-selected Ag cluster anions, AgN - (N = 3, 7, 14), and show that each image can be obtained in a short accumulation time (50 s) with a kinetic energy resolution (ΔE/E) of 4% at E = 1.77 eV. The quasi-continuous PEI technique enables high-count-rate, space-charge-free acquisition of photoelectron spectra and angular distributions not only from size-selected metal cluster anions but also from anions prepared by other continuous ion sources, such as electrospray ionization.

Design and characterization of a magnetic bottle electron spectrometer for time-resolved extreme UV and X-ray photoemission spectroscopy of liquid microjets.

We describe a magnetic bottle time-of-flight electron spectrometer designed for time-resolved photoemission spectroscopy of a liquid microjet using extreme UV and X-ray radiation. The spectrometer can be easily reconfigured depending on experimental requirements and the energy range of interest. To improve the energy resolution at high electron kinetic energy, a retarding potential can be applied either via a stack of electrodes or retarding mesh grids, and a flight-tube extension can be attached to increase the flight time. A gated electron detector was developed to reject intense parasitic signal from light scattered off the surface of the cylindrically shaped liquid microjet. This detector features a two-stage multiplication with a microchannel plate plus a fast-response scintillator followed by an image-intensified photon detector. The performance of the spectrometer was tested at SPring-8 and SACLA, and time-resolved photoelectron spectra were measured for an ultrafast charge transfer to solvent reaction in an aqueous NaI solution with a 200 nm UV pump pulses from a table-top ultrafast laser and the 5.5 keV hard X-ray probe pulses from SACLA.

Ultrafast Ring-Opening Reaction of 1,3-Cyclohexadiene: Identification of Nonadiabatic Pathway via Doubly Excited State.

The photoinduced ring-opening reaction of 1,3-cyclohexadiene (CHD) to produce 1,3,5-hexatriene (HT) plays an essential role in the photobiological synthesis of vitamin D3 in the skin. This reaction follows the Woodward-Hoffmann rule, and C5-C6 bond rupture via an electronically excited state occurs with conrotatory motion of the end CH2 groups. However, it is noted that the photoexcited S1(π,π*) state of CHD is not electronically correlated with the ground state of HT, and the reaction must proceed via nonadiabatic transitions. In the present study, we have clearly observed the nonadiabatic reaction pathway via the doubly excited state of CHD using ultrafast extreme UV photoelectron spectroscopy. The results indicate that the reaction occurs in only 68 fs and creates product vibrational coherence. Extensive computational simulations support the interpretation of experimental results and provide further insights into the electronic dynamics in this paradigmatic electrocyclic ring-opening reaction.

Time-Resolved Photoelectron Imaging of Acetone with 9.3 eV Photoexcitation.

Ultrafast electronic relaxation following 9.3 eV photoexcitation of gaseous acetone was investigated with time-resolved photoelectron imaging spectroscopy. An intense photoionization signal due to a transition from the 41A1(π,π*) state to the D1(π-1) cationic state diminishes within 50 fs, owing to vibrational wave packet motion leaving our observation energy window. Additional photoionization signals were assigned to transitions from Rydberg states with principal quantum numbers of 3-8 to the D0(n-1) cationic state, created by strong vibronic couplings with the bright 41A1(π,π*) state. The deactivation processes of the 41A1(π,π*) and Rydberg states are discussed based on their decay profiles obtained from a time-energy map of photoelectron kinetic energy distributions.

Real-time detection of S(1D2) photofragments produced from the 1B2(1Σu+) state of CS2 by vacuum ultraviolet photoelectron imaging using 133 nm probe pulses.

Ultrafast photodissociation dynamics from the 1B2(1Σu+) state of CS2 are studied by time-resolved photoelectron imaging using the fourth (4ω, 198 nm) and sixth (6ω, 133 nm) harmonics of a femtosecond Ti:sapphire laser. The 1B2 state of CS2 was prepared with the 4ω pulses, and subsequent dynamics were probed using the 6ω vacuum ultraviolet (VUV) pulses. The VUV pulses enabled real-time detection of S(1D2) photofragments, produced via CS2*(1B2(1Σu+)) → CS(X 1Σ+) + S(1D2). The photoionization signal of dissociating CS2*(1B2(1Σu+)) molecules starts to decrease at about 100 fs, while the S(1D2) fragments appear with a finite (ca. 400 fs) delay time after the pump pulse. Also discussed is the configuration interaction of the 1B2(1Σu+) state based on relative photoionization cross-sections to different cationic states.

Successful Resection of a Large Rectal Adenoma Using the Transsacral Approach.

The transsacral approach is not routinely used for treating rectal tumors. We report the case of a 65-year-old man with a large adenoma at the posterior wall of the mid-rectum who was treated via the transsacral approach. The same lesion had been treated using transsacral endoscopic microsurgery 8 years previously. Moreover, 11 years previously he had undergone a laparotomy for bladder cancer, and an Indiana pouch had been constructed. Abdominal computed tomography showed that the pouch was adjacent to the rectum. Therefore, the less-invasive transsacral approach, rather than the transabdominal approach, was chosen for treatment. The lesion was successfully resected, without disturbing the pouch. Histological analysis indicated tubular adenoma, with a small focus of intramucosal adenocarcinoma, and negative margins. Thus, we achieved successful resection of mid-rectal lesions via the transsacral approach, without the morbidity associated with major laparotomy. We suggest that this procedure should be a part of a surgeon's armamentarium.

Full observation of ultrafast cascaded radiationless transitions from S2(ππ(∗)) state of pyrazine using vacuum ultraviolet photoelectron imaging.

A photoexcited molecule undergoes multiple deactivation and reaction processes simultaneously or sequentially, which have been observed by combinations of various experimental methods. However, a single experimental method that enables complete observation of the photo-induced dynamics would be of great assistance for such studies. Here we report a full observation of cascaded electronic dephasing from S2(ππ(*)) in pyrazine (C4N2H4) by time-resolved photoelectron imaging (TRPEI) using 9.3-eV vacuum ultraviolet pulses with a sub-20 fs time duration. While we previously demonstrated a real-time observation of the ultrafast S2(ππ(*)) → S1(nπ(*)) internal conversion in pyrazine using TRPEI with UV pulses, this study presents a complete observation of the dynamics including radiationless transitions from S1 to S0 (internal conversion) and T1(nπ(*)) (intersystem crossing). Also discussed are the role of (1)Au(nπ(*)) in the internal conversion and the configuration interaction of the S2(ππ(*)) electronic wave function.

Ultrafast photodynamics of pyrazine in the vacuum ultraviolet region studied by time-resolved photoelectron imaging using 7.8-eV pulses.

The ultrafast electronic dynamics of pyrazine (C4N2H4) were studied by time-resolved photoelectron imaging (TRPEI) using the third (3ω, 4.7 eV) and fifth harmonics (5ω, 7.8 eV) of a femtosecond Ti:sapphire laser (ω). Although the photoionization signals due to the 5ω - 3ω and 3ω - 5ω pulse sequences overlapped near the time origin, we have successfully extracted their individual TRPEI signals using least squares fitting of the observed electron kinetic energy distributions. When the 5ω pulses preceded the 3ω pulses, the 5ω pulses predominantly excited the S4 (ππ(*), (1)B1 u+(1)B2u) state. The photoionization signal from the S4 state generated by the time-delayed 3ω pulses was dominated by the D3((2)B2g)←S4 photoionization process and exhibited a broad electron kinetic energy distribution, which rapidly downshifted in energy within 100 fs. Also observed were the photoionization signals for the 3s, 3pz, and 3py members of the Rydberg series converging to D0((2)Ag). The Rydberg signals appeared immediately within our instrumental time resolution of 27 fs, indicating that these states are directly photoexcited from the ground state or populated from S4 within 27 fs. The 3s, 3pz, and 3py states exhibited single exponential decay with lifetimes of 94 ± 2, 89 ± 2, and 58 ± 1 fs, respectively. With the reverse pulse sequence of 3ω - 5ω, the ultrafast internal conversion (IC) from S2(ππ(*)) to S1(nπ(*)) was observed. The decay associated spectrum of S2 exhibited multiple bands ascribed to D0, D1, and D3, in agreement with the 3ω-pump and 6ω-probe experiment described in our preceding paper [T. Horio et al., J. Chem. Phys. 145, 044306 (2016)]. The electron kinetic energy and angular distributions from S1 populated by IC from S2 are also discussed.

Ultrafast Deactivation of the ππ*(V) State of Ethylene Studied Using Sub-20 fs Time-Resolved Photoelectron Imaging.

The ultrafast deactivation process of ethylene in the ππ*(V) state was studied using time-resolved photoelectron imaging with sub-20 fs pulses at 159 and 198 nm. The photoelectron kinetic energy distribution observed upon 159 nm photoexcitation exhibited a continuous downward shift within 20 fs, attributed to both C-C twist and pyramidalization motions. A partial revival of the vibrational wave packet was observed with the period of about 18 fs, which is attributed to the C-C twist from 0 to 180° on the ππ*(V) potential energy surface. Signature for internal conversion from the ππ*(V) state to a lower-lying π3s Rydberg (R) state, which has been previously suggested, was not detected in the time-dependent photoelectron kinetic energy and angular distributions.

Generation of sub-17 fs vacuum ultraviolet pulses at 133 nm using cascaded four-wave mixing through filamentation in Ne.

The sixth harmonic (6ω, 133 nm) of a Ti:sapphire laser is generated using cascaded four-wave mixing in filamentation propagation of the fundamental (ω) and the second harmonic (2ω) pulses through Ne gas. The method provides the 6ω pulse energy higher than 5 nJ/pulse at 1 kHz and a pulse duration shorter than 17 fs without dispersion compensation.

Time- and angle-resolved photoemission spectroscopy of hydrated electrons near a liquid water surface.

We present time- and angle-resolved photoemission spectroscopy of trapped electrons near liquid surfaces. Photoemission from the ground state of a hydrated electron at 260 nm is found to be isotropic, while anisotropic photoemission is observed for the excited states of 1,4-diazabicyclo[2,2,2]octane and I- in aqueous solutions. Our results indicate that surface and subsurface species create hydrated electrons in the bulk side. No signature of a surface-bound electron has been observed.

Photoelectron spectroscopy of aqueous solutions: streaming potentials of NaX (X = Cl, Br, and I) solutions and electron binding energies of liquid water and X-.

The streaming potentials of liquid beams of aqueous NaCl, NaBr, and NaI solutions are measured using soft X-ray, He(I), and laser multiphoton ionization photoelectron spectroscopy. Gaseous molecules are ionized in the vicinity of liquid beams and the photoelectron energy shifts are measured as a function of the distance between the ionization point and the liquid beam. The streaming potentials change their polarity with concentration of electrolytes, from which the singular points of concentration eliminating the streaming potentials are determined. The streaming currents measured in air also vanish at these concentrations. The electron binding energies of liquid water and I(-), Br(-), and Cl(-) anions are revisited and determined more accurately than in previous studies.

Simultaneous generation of sub-20 fs deep and vacuum ultraviolet pulses in a single filamentation cell and application to time-resolved photoelectron imaging.

Sub-20 fs pulses of the third, fourth, and fifth harmonics of a Ti:sapphire laser are simultaneously generated using cascaded four-wave mixing in filamentation propagation of the fundamental frequency and the second harmonic pulses in Ne gas. Reflective optics under vacuum are employed after the four-wave mixing to minimize material dispersion of the optical pulses. The cross-correlation between 198 and 159 nm pulses of 18 fs is achieved without dispersion compensation. This new light source is applied to time-resolved photoelectron imaging of carbon disulfide (CS2).

Effects of platelet-rich plasma-containing fragmin/protamine microparticles in enhancing endothelial and smooth muscle cell growth and inducing collateral vessels in a rabbit model of hindlimb ischemia.

The purpose of the study was to evaluate the effects of isogenous platelet-rich plasma (PRP)-containing fragmin/protamine microparticles (F/P MPs) as a delivery system for proteins in PRP on growth of endothelial and smooth muscle cells (SMCs) in vitro and as an alternative treatment for peripheral arterial disease (PAD) and critical limb ischemia. Frozen and thawed PRP contains high concentrations of growth factors that are adsorbed by F/P MPs. Human aorta endothelial cells (AECs) and SMCs were grown in a medium with PRP. Addition of F/P MPs significantly enhanced the proliferative effects of PRP on AECs and SMCs at 37 °C for >10 days. Intramuscular administration of phosphate-buffered saline (PBS; 2 mL, control), F/P MPs (12 mg in 2 mL PBS), PRP (2 mL), or PRP (2 mL) containing F/P MPs (12 mg) was then performed in a rabbit model of hindlimb ischemia prepared by resection of the left femoral artery. Blood flow and pressure were measured on days 0, 14, and 28, and angiography to assess arteriogenesis was performed on day 28. PRP-containing F/P MPs strongly induced functional collateral vessels in the rabbit model of hindlimb ischemia, indicating possible use of these microparticles in therapy for PAD.

Esophageal cancer initially thought to be accompanied by a solitary metastasis to an intrathoracic paraaortic lymph node.

Esophageal cancers usually exhibit lymph-node metastases. Although a solitary lymph-node metastasis is occasionally found, the involvement of an intrathoracic paraaortic node is rare. We present here an intrathoracic mid-esophageal cancer case in which an accompanying solitary retroaortic mass was found within the posterior mediastinum by integrated positron emission tomography/computed tomography. For diagnosis, thoracoscopic resection of the mass was performed from a left thoracic approach, and histology revealed it to be a squamous cell carcinoma metastasized from the esophageal cancer. Upon radical esophagectomy after neoadjuvant therapy as a T3N1M0 Stage IIIa (AJCC/UICC) cancer, the esophageal cancer was found to have invaded unexpectedly deeply in the vicinity of the descending aorta. Another lymph node within the paraaortic region was also involved (T4N1M0 Stage IIIc). The present case and other cases we review here inform our understanding of metastasis to intrathoracic paraaortic nodes as follows:1) its existence may indicate extensive lymph-node metastasis or direct tumor invasion nearby, and 2) it may be accompanied by other lymph-node involvements in this region, even if it appears solitary upon preoperative investigation. Thus, for radical esophagectomy, sufficient lymph-node dissection is required, even at locations not reached by the usual right thoracic approach. Definitive chemoradiotherapy may be a better choice for preoperatively recognized T3 esophageal cancer when the cancer is accompanied by paraaortic lymph node metastasis.

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.

Endoscopic submucosal dissection for pig esophagus by using photocrosslinkable chitosan hydrogel as submucosal fluid cushion.

BACKGROUND: Hypertonic saline solution (HS) as a submucosal fluid cushion (SFC) for endoscopic submucosal dissection (ESD) has several disadvantages, including a short effect duration and increased risk of bleeding and perforation. Photocrosslinkable chitosan hydrogel in DMEM/F12 medium (PCH) can be converted into an insoluble hydrogel by UV irradiation for 30 seconds. OBJECTIVE: To evaluate the feasibility, usefulness, and safety of PCH as an SFC for ESD of esophagi, compared with HS and sodium hyaluronate (SH). DESIGN: Survival animal study. SETTINGS: Research laboratory study of 24 pig models in vivo. INTERVENTIONS: Twenty-four pigs were used in the 2 steps: First, ESD of the esophagus was performed with PCH, SH, or HS (each n = 6) as an SFC, and the effects of these agents on wound healing were examined endoscopically and histologically. Second, in vivo degradation of PCH (n = 3) and HS (n = 3) was examined in independent pig esophagi. MAIN OUTCOME MEASUREMENTS: Outcome measurements included feasibility and safety of PCH-assisted ESD of esophagus, gross and histologic evidence of the treated esophagus, biodegradation of injected PCH, and clinical tolerance by the animals. RESULT: PCH injection led to a longer-lasting elevation with clearer margins compared with SH and HS, thus enabling precise ESD along the margins of the elevated mucosa without complications such as bleeding and perforation. The aspects of wound repair after PCH-assisted ESD were similar to those of SH- and HS-assisted ESDs. Biodegradation of PCH was confirmed to be almost completed within 8 weeks on the basis of endoscopic and histologic observations. LIMITATIONS: In vivo animal model study. CONCLUSION: PCH permits more reliable ESD of the esophagus without complications than do SH and HS. Furthermore, the applied PCH appeared to be completely biodegraded within 8 weeks. Thus, PCH is a promising agent as an SFC in ESD of the esophagus.

Two-color deep-ultraviolet 40-fs pulses based on parametric amplification at 100 kHz.

We present a 100-kHz deep-ultraviolet (DUV) laser system that generates 40-fs pulses. A 520-nm pulse generated by a noncollinear optical parametric amplifier pumped by the second harmonic of a Ti:sapphire laser is converted into 226- and 260-nm DUV pulses simultaneously with pulse energies of 250 and 130 nJ (average powers: 25 and 13 mW), respectively. The DUV pulses were estimated to have durations of ca. 40 fs by cross-correlation measurements based on (1 + 1') two-color ionization of gaseous nitric oxide.