The absolute values of the effective attenuation length of an electron in liquid water are determined using soft x-ray O1s photoemission spectroscopy of a liquid beam of water without employing any theoretical estimation or computationally obtained value. The effective attenuation length is greater than 1 nm in the entire electron kinetic energy region and exhibits very flat energy dependence in the 10-100 eV region.

High-resolution soft X-ray photoelectron spectra of liquid water (H(2)O and D(2)O) were measured using a liquid beam photoelectron spectrometer. The 1a(1) (O1s) band and the lowest valence 1b(1) band had single peaks, which is not consistent with the split 1b(1)→ 1a(1) of the X-ray emission band of liquid water if the splitting is assumed to originate from level shifts in two different hydrogen bonding structures. The second valence 3a(1) band of liquid water exhibited a flat top implying that two bands exist underneath a broad feature, which is similar to the case of the 3a(1) band of amorphous ice. The energy splitting between the two 3a(1) bands is estimated to be 1.38 eV (H(2)O) and 1.39 eV (D(2)O). Ab initio calculations suggest that the large splitting of the 3a(1) band is characteristic of water molecules that function as both proton donor and acceptor. The overall result is consistent with the conventional model of a tetrahedral hydrogen-bonding network in liquid water.

Time-resolved photoelectron spectroscopy (TR-PES) of ultrafast dynamics in solution is presented. To measure the photoelectron kinetic energy distribution (PKED) that is free from inelastic scattering in solution, photoelectrons were generated with ultra-low kinetic energies (ULKE: <5 eV). Time constants of the elementary processes in the charge-transfer-to-solvent (CTTS) reaction from Ito bulk water were in excellent agreement with those obtained by transient absorption spectroscopy, demonstrating the bulk-sensitivity of TR-PES-ULKE. The analysis suggests that the CTTS reaction proceeds via two intermediates, and that 30% of the first intermediate and 70 % of the second intermediate respectively are quenched by geminate recombination between the electron and the neutral iodine atom.

Magnetic field effects (MFEs) due to the isotropic Δg mechanism were studied for the hydrogen abstraction reactions of 4-methoxy-benzophenone with thiophenol in several solvents at 293 K by a laser flash photolysis technique under ultrahigh magnetic fields of up to 30 T. In 2-propanol, ethanol, and methanol, the yield of the escaped ketyl radical decreased with increasing magnetic field from 0 to 30 T. In 2-methyl-1-propanol, however, the decrease was almost saturated at 20 T and the yield above 20 T reduced to be 2/3 of that at 0 T. Such saturation of the MFEs due to the isotropic Δg mechanism in the reaction through radical pairs in solution was found for the first time.

We have studied 3s(n-1 and pi-1) Rydberg states and D0(n-1) and D1(pi-1) cationic states of pyrazine [1,4-diazabenzene] by picosecond (2 + 1) resonance-enhanced multiphoton ionization (REMPI), (2 + 1) REMPI photoelectron imaging, He(I) ultraviolet photoelectron spectroscopy (UPS), and vacuum ultraviolet pulsed field ionization photoelectron spectroscopy (VUV-PFI-PE). The new He(I) photoelectron spectrum of pyrazine in a supersonic jet revealed a considerably finer vibrational structure than a previous photoelectron spectrum of pyrazine vapor. We performed Franck-Condon analysis on the observed photoelectron and REMPI spectra in combination with ab initio density functional theory and molecular orbital calculations to determine the equilibrium geometries in the D0 and 3s(n-1) states. The equilibrium geometries were found to differ slightly between the D0 and 3s states, indicating the influence of a Rydberg electron on the molecular structure. The locations of the D1-D0 and 3s(pi-1)-3s(n-1) conical intersections were estimated. From the line width in the D1 <-- S0 spectrum, we estimated the lifetime of D1 to be 12 fs for pyrazine and 15 fs for fully deuterated pyrazine. A similar lifetime was estimated for the 3s(pi-1) state of pyrazine by REMPI spectroscopy. The vibrational feature of D1 observed in the VUV-PFI-PE measurement differed dramatically from that in the UPS spectrum, which suggests that the high-n Rydberg (ZEKE) states converging to the D1 vibronic state are short-lived due to electronic autoionization to the D0 continuum.

We performed He I ultraviolet photoelectron spectroscopy (UPS) of jet-cooled aromatic molecules using a newly developed photoelectron imaging (PEI) spectrometer. The PEI spectrometer can measure photoelectron spectra and photoelectron angular distributions at a considerably higher efficiency than a conventional spectrometer that uses a hemispherical energy analyzer. One technical problem with PEI is its relatively high susceptibility to background electrons generated by scattered He I radiation. To reduce this problem, we designed a new electrostatic lens that intercepts background photoelectrons emitted from the repeller plate toward the imaging detector. An energy resolution (ΔE/E) of 0.735% at E = 5.461 eV is demonstrated with He I radiation. The energy resolution is limited by the size of the ionization region. Trajectory calculations indicate that the system is capable of achieving an energy resolution of 0.04% with a laser if the imaging resolution is not limited. Experimental results are presented for jet-cooled benzene and pyridine, and they are compared with results in the literature.

A water-cooled pulsed magnet having a room temperature bore of diameter 20 mm was constructed. Magnetic field effects on a triplet sensitization reaction of p-aminophenyl disulfide (APDS) with xanthone (Xn) were studied in a sodium dodecylsulfate (SDS) micellar solution by a nanosecond laser flash photolysis technique under ultrahigh magnetic fields of up to 28 T. Upon irradiation of the SDS micellar solution containing APDS and Xn, triplet radical pairs of p-aminophenylthiyl radicals were generated. The yield of the escaped p-aminophenylthiyl radical was found to decrease by 6 AE 2% at 28 T compared with that at 0 T.

Magnetic field effects (MFEs) on chemical reactions have been extensively studied during the last two decades. 1,2 The MFEs on reactions of radical pairs in solution can be interpreted by the radical pair mechanism. The conversion between the triplet (T m ) and singlet (S) radical pairs arises from the following mechanism: [1][2][3][4] (1) the ∆g mechanism (∆gM) which is due to the difference between the isotropic g-factors of two radicals in the pair, (2) the hyperfine coupling mechanism (HFCM) due to the isotropic hyperfine interaction between electron and nuclear spins, (3) the level-crossing mechanism due to the crossing of the S and T (1 levels, and (4) the relaxation mechanism (RM) due to the anisotropic g-tensor (δg), HFC, and spin-spin dipolar interactions. Thus, the radical pair lifetime (τ RP ) and the escape radical yield (Y(B)) are influenced by external magnetic fields. According to the ∆gM, 3 the τ RP and Y values from a triplet precursor should decrease with increasing magnetic field (B) because the T 0 -S spin conversion rate increases with increasing B. Such MFEs due to the ∆gM have been studied extensively under magnetic fields below 10 T, 1,2,5-12 where the changes in Y due to the ∆gM are theoretically predicted to be proportional to B 1/2 . 1-3,13 Experimentally, good linear relationships between R(B) () Y(B)/Y(0)) and B 1/2 have been obtained. 1,5,6,11,12 Recently, the saturation and reversion of MFEs under high fields (10 T e B e B max ) have been found for several reactions of organic radical pairs (B max ) 10 T) 2 , biradicals (B max ) 14 T), 14 and Ru complexes (B max ) 17.5 T). 15 Such saturation and reversion have been interpreted in terms of the spin relaxation due to anisotropic δg-, HFC-, and dipolar-interactions. There has been, however, no report on the saturation of the MFEs due to the isotropic ∆gM. Theoretically, Schulten and Epstein predicted that such ∆g-induced saturation of MFEs would occur at extremely large magnetic field values of the order of 10 3 T for ∆g on the order of 0.01 in nonviscous solvent. 13 Because this prediction was obtained by the special selection of various unknown parameters, it is possible that the saturation field may be lowered if the parameters are chosen otherwise.In 1997, we constructed a laser flash photolysis apparatus with a pulsed magnet to measure the MFEs on dynamic behavior of radical pairs under ultrahigh magnetic fields of up to 30 T. 16 We, therefore, have challenged the above-mentioned prediction and tried to find saturation behavior of the MFEs due to the isotropic ∆gM with this apparatus, measuring the hydrogen abstraction reaction of 4-methoxybenzophenone with thiophenol in 2-methyl-1-propanol. We observed that Y(B) values of the ketyl radical decreased with increasing B from 0 to 10 T, but the decrease was almost saturated at 20 T. The saturated Y(B) value was 2 / 3 of the Y(0 T) one. To the best of our knowledge, this is the first observation of the saturation effect of the MFEs due to the isotropic ∆g mechanism.In the photochem...