Mass-resolved velocity map images have been measured for C60−2n2+ and C60−2n3+ (n ≥ 1) produced by photoionization of C60 with synchrotron radiation. A four-element electrostatic compound lens syst...

A photoionization spectrometer for velocity map imaging has been developed for measuring the scattering distribution of fragment ions from polyatomic molecules. The spectrometer contains a mass gate and an ion reflector which are able to discriminate ions with a particular mass-to-charge ratio m/z . The basic functions and feasibility of these devices were tested experimentally and theoretically. First, the photoions from Kr and C 60 were extracted into a time-of-flight (TOF) mass spectrometer by a transient or continuous electrostatic field. When the pulse application on the mass gate was tuned to the arrival timing of ions with a specific m/z , the peak of the selected ions alone was present on a TOF spectrum. Second, compatibility between velocity map imaging and ion discrimination was investigated by the computer simulations of the ion trajectories of photofragments from C 60 . A pulsed voltage was applied to the mass gate synchronously with the arrival timing of C58+ ions. The initial three-dimensional velocity distribution of C58+ was projected onto the image plane with an energy resolution better than 10 meV. The C58+ image was free from the contamination of other ions such as C60+ and C56+.

Dye-sensitized solar cells were fabricated using eight azo dyes which have different positions and/or numbers of carboxyl and hydroxyl groups. The short-circuit current density, photoabsorbance, absorptance and quantum yield for dyes-to-TiO2 electron injection were measured by photons ranging from 380 to 800nm. X-ray and ultraviolet photoelectron spectroscopy of the photovoltaic electrodes were also conducted. The photon-to-current conversion efficiency of the cells was found to depend mostly on the relative position of the lowest unoccupied molecular orbital of the adsorbed dyes and partly by their concentration on the TiO2 nanoparticles.

The velocity distributions of the fragments produced by dissociative photoionization of C(70) have been measured at several photon energies in the extreme UV region, by using a flight-time resolved velocity map imaging (VMI) technique combined with a high-temperature molecular beam and synchrotron radiation. Average kinetic energy release was estimated for the six reaction steps of consecutive C(2) emission, starting from C(70)(2+) → C(68)(2+) + C(2) to C(60)(2+)→ C(58)(2+) + C(2). The total kinetic energy generated in each step shows a general tendency to increase with increasing hν, except for the first and fifth steps. This propensity reflects statistical redistributions of the excess energy in the transition states for the above fragmentation mechanism. Analysis based on the finite-heat-bath theory predicts the detectable minimum cluster sizes at the end of the C(2)-emission decay chain. They accord well with the minimum sizes of the observed ions, if the excess energy in the primary C(70)(2+) is assumed to be smaller by ~15 eV than the maximum available energy. The present VMI experiments reveal remarkably small kinetic energy release in the fifth step, in contradiction to theoretical predictions, which suggests involvement of other fragmentation mechanisms in the formation of C(60)(2+).

The velocity distributions of the fragments produced by dissociative photoionization of C60 have been measured in the extreme UV region for the first time, by using a flight-time resolved velocity map imaging technique combined with a high-temperature molecular beam and synchrotron radiation. Values of the average kinetic energy release were estimated at six different photon energies with respect to five reaction steps of sequential C2 ejection, starting from C602+→C582++C2 to C522+→C502++C2. The translational temperatures of the fragment ions were found to be lower than those obtained by laser multiphoton absorption of C60. The kinetic energies released in the first to fourth steps increase with increasing hν and reach 0.35–0.5 eV at hν=102 eV, reflecting statistical redistribution of the excess energy in the transition state, whereas that in the fifth step leading to C502+ was exceptionally small.

A velocity map imaging (VMI) spectrometer was constructed for observation of the slow ions produced by photofragmentation of C60 with synchrotron radiation. The spectrometer was tested by observing the ion images of rare gases in the Maxwell–Boltzmann distribution at room temperature, and the effect of a large ionization volume inevitable in our experiment has been quantitatively characterized. Numerical simulations taking into account such instrumental parameters indicate that one can distinguish the two independent formation processes of C56+ from the primary precursor C60+: i.e., one-step ejection of C4 and sequential ejections of two C2 fragments.

The absolute total photoionization cross section sigma(abs),(I) of gaseous C-60 is measured in the photon energy hv range from 25 to 120eV by photoionization mass spectrometry with synchrotron radiation. The absolute detection efficiencies of photoions in different charge states are evaluated. The present sigma(abs,I) curve is combined with the photoabsorption cross section curves of C-60 at hv = 3.5-26eV in the literature, after appropriate alterations of the vapor pressure are taken into account. The oscillator strengths are computed from the composite curve to be 178.5 and 230.5 for the hv ranges from 3.5 to 40.8 eV and from 3.5 to 119 eV, respectively. These oscillator strengths agree well with those expected from the Thomas-Kuhn-Reiche sum rule and 60 times the photoabsorption cross section of a carbon atom. Moreover, the present sigma(abs,I) curve behaves similarly to the relative photoionization cross section curve reported by Reinkoster et al.

1 Department of Photo-molecular Science, The Institute for Molecular Science, Myodaii, Okazaki 444-8585, Japan Graduate University for Advanced Studies, Myodaii, Okazaki 444-8585, Japan Hosei University Introduction The dissociation dynamics of C60 has been studied by many experimental methods, such as photoionization mass spectrometry electron impact ionization, slow highly-charged-ion collision and heavy-ion excitation since the discovery of the fullerene molecule in 1985. Today it is commonly accepted that the dominant fragmentation mechanism involves the sequential loss of C2 units from energized C60*. Moreover, a huge kinetic shift has been found when a C2 unit is removed from the parent ion. The larger kinetic shift is caused by many degrees of freedom and a very tight and symmetric structure of C60. However, the dissociation and fragmentation of C60 after single-photon excitation has been studied in very few papers. Yoo et al. have observed C60→ C58 + C2 fragmentation at hν of 41eV. Reinkoster et al. and Juranic et al. have reported experimental results for the ionization and fragmentation of C60 by using synchrotron radiation in the hν range 26-130eV and 18-280eV, respectively. Since 2003, our group has studied the photoionization and photodissociation of fullerene molecules combining extreme vacuum violet synchrotron radiation from the beamline BL2B at the UVSOR in Okazaki. We have measured the yield curves of the fragments produced from photoionization of C60 and C70 by time-of-flight (TOF) mass spectrometry to study the dissociative mechanisms and kinetics. Namely, the yield curves for CK-

The photoion yield spectra of an endohedral metallofullerene Pr@C82 were measured in the photon energy range of 100–150eV by using time-of-flight mass spectrometry. Parent ions Pr@C82+, Pr@C822+ and Pr@C823+ were observed in the mass spectra. The photoion yield spectra of Pr@C822+ showed a broad peak at 120–140eV that was assigned to the 4d–4f giant dipole resonance of the encapsulated Pr atoms. Absolute photoabsorption cross sections of Pr@C82 were evaluated from the photoion yield spectra to be 37±12Mb at 110eV (off-resonance) and 52±13Mb at 130eV (on-resonance). These cross sections of Pr@C82 were compared with the results of Ce@C82, the only metallofullerene whose photoionization properties have ever been studied near the 4d edge of the encapsulated metal atom. The enhancement of photoabsorption due to the giant resonance was found to be similar in Pr@C82 and Ce@C82, but there are marked differences in the peak shapes, which can be explained as due to interference effects between the fullerene cage and the encapsulated metal atoms.

1-Butyl-3-methylimidazolium bromide ([bmim]Br) and its chloride ([bmim]Cl) are representative prototypes of ionic liquids. We investigated the melting and freezing behaviors of [bmim]Br and [bmim]Cl by using a homemade differential scanning calorimeter (DSC) with nano-Watt stability and sensitivity. The measurements were carried out at heating and cooling rates slow enough to mimic quasi-static processes. Their thermal behaviors of melting and freezing show characteristic features such as a wide pre-melting range and excessive supercooling and individual behaviors of single crystals even for the same substance. The melting temperatures of [bmim]Br and [bmim]Cl were determined from the broad DSC traces and discussed in relation to the crystal structure. We suggest that the observed characteristics are due to the dynamics of the cooperative change between gauche-trans (GT) and trans-trans (TT) conformations of the butyl group in the [bmim](+) cation.

Partial cross sections for the photoion formation from C(60) and C(70) were determined from the yields of singly, doubly, and triply charged ions which were measured by mass spectrometry combined with tunable synchrotron radiation at hnu = 25-120 eV. The dependence of the detection efficiencies on the mass-to-charge ratio was evaluated by using the formula proposed by Twerenbold et al. Corrections of the detection efficiency were found to be critical for obtaining accurate partial cross sections for photoionization of fullerenes. Revisions were made of the partial cross-section curves for single and double photoionization of C(60) and C(70). The curve for triple photoionization of C(70) was newly proposed. The ratios between the cross sections for double and single photoionization increase with hnu and reach saturated values of 0.78 at 85 eV for C(60) and approximately 1.3 at 100 eV for C(70). In contrast, the ratios at 120 eV between the cross sections for triple and single photoionization of C(60) and C(70) amount to 0.14 and approximately 0.38, respectively. The formation mechanism of multiply charged fullerene ions was discussed in terms of valence-electron excitation to antibonding unoccupied orbitals and/or spherical standing waves inside the cavity of a fullerene. This excitation could be followed by Spectator Auger processes and transmission of the excess electronic energy among numerous vibrational degrees of freedom.

Description is made on a design of a new version of photofragment imaging spectrometer which will be applied to observe the momentum distributions of ionic fragments from large molecules, clusters, and fullerenes. The apparatus consists of several components: a three‐element velocity focusing lens system, a time‐of‐flight drift tube, a potential‐switcheable mass gate, an ion reflector, and a position sensitive detector. The velocity focusing lens system of Eppink‐Parker type [Eppink and Parker, Rev. Sci. Instrum. 68, 3477 (1997)] realizes high‐resolution photofragment images. Moreover, the mass gate is incorporated inside the tube in order to separate fragment ions with a particular cluster size (e.g. C58+) from those with other sizes (e.g. C60+ and C56+). The optimum arrangement and dimensions of the components are determined from the results of ion trajectories of C56+, C58+, and C60+ simulated by using the SIMON software. The calculated images of C58+ ions show that kinetic‐energy resolution of 10 meV ...

We use the thermodynamic behaviour of I-propanol (1P) as a probe in ternary 1P-salt-H2O systems to elucidate the effect of a salt on the molecular organization of H2O. For salts, we have chosen CaCl2, NH4Cl, and (CH3)(4)NCl (TMAC). Having fixed the counter anion at Cl-, we compare here mainly the effects of chosen cations on H2O. Together with an earlier study on NaCl, we found that Ca2+, Na+, and NH4+ are hydrated by a number of H2O molecules and leave the bulk H2O away from the hydration shell unperturbed. The hydration numbers were found to be 6.4 +/- 1.6, and 1.2 +/- 0.4, for Ca2+ and NH4+, respectively with the hydration number 5.2 for Na+, the result of a simulation study, chosen as a reference. Thus, a salting out (also referred to as structure making, stabilizing, or kosmotropic) tendency would decrease in the order; Ca2+ > Na+ > NH4+. TMA(+), on the other hand, showed a more hydrophilic characteristics than the probing 1P. Thus, TMA(+) is rather chaotropic (salting in, structure breaking or destabilizing) within this methodology.

A novel method of determining a liquid–liquid phase boundary was developed. This method is based on our discovery that a nascent low-density phase is attracted to the center of a Rankine vortex at the onset of phase separation. Thus a liquid–liquid phase boundary is detected easily, rapidly, and accurately. The phase diagrams of the ternary systems NaCl–H2O–1-propanol and NaCl–H2O–1-butanol were obtained by this method. The results matched well with literature values.

The structure of a room temperature ionic liquid (IL), 1-n-butyl-3-methylimidazolium iodide ([bmim]I), is studied by wide-angle X-ray scattering (WAXS) and Raman spectroscopy. The radial distribution function obtained by WAXS shows prominent peaks ascribable to a structure constructed by iodide anions; this means that the structure of the anions has a long-range correlation. The Raman spectrum of liquid [bmim]I agrees with those of [bmim]Cl and [bmim]Br in the molten phase and in crystals. The results show that the cation structures in the liquids of three [bmim] halides are similar to those in the crystals. However, the arrangement of the iodide anions in liquid [bmim]I differs slightly from those in crystalline [bmim]Cl and [bmim]Br, although it partly retains the hydrophilic channel structure characteristic of the crystals.

We studied a detailed thermodynamic behavior of 1-propanol (abbreviated as 1P) in mixed solvents of aqueous Na2SO4, NaOOCCH3, and NaClO4, and NaSCN. We measured the excess partial molar enthalpy of 1P, H-1P(E), in these mixed solvents at various initial salt concentrations. We then evaluated what we call the enthalpic interaction, H-1P-1P(E) = (partial derivativeH(1P)(E)/partial derivativen(1P)), where n(1P) is the amount of 1P. The composition dependence of H-1P-1P(E) changes in a characteristic manner on addition of a specific salt. This induced change in the behavior of H-1P-1P(E) is used to elucidate the effect of the salt on the molecular organization of H2O. Na+ ion seems to hydrate a number less than seven or eight molecules of H2O, leaving the bulk H2O outside the hydration shell unperturbed. SO42- also hydrates a number less than 26 H2O molecules with a concomitant increase in the degree of fluctuation of the bulk H2O. Na2SO4 as a whole hydrates the total of 26 H2O. CH3COO- ion modifies H2O in a similar manner as an alcohol. Cl- ion hydrates a number less than seven or eight H2O molecules leaving the bulk H2O in the same state as in pure H2O. NaCl as a whole hydrates the total of seven or eight molecules of H2O. ClO4- and SCN- participate in hydrogen bonding with the hydrogen bond network of H2O keeping its connectivity intact. However, they reduce the degree of fluctuation inherent in liquid H2O. Thus, each ion has its own unique manner of modifying H2O, except that ClO4- and SCN- modify H2O in almost the same way. Therefore, it seems fair to state that the phenomenological net result manifested as the Hofmeister series is due to multifacetted factors working in the holistic manner, and a single or a small number of parameters is not sufficient to explain its effect.

We studied the hydration characteristics of room-temperature ionic liquids (IL). We experimentally determined the excess chemical potentials, mu(i)(E), the excess partial molar enthalpies, H-i(E), and the excess partial molar entropies S-i(E) in IL-H2O systems at 25 degreesC. The ionic liquids studied were 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF4) and the iodide ([bmim]l). From these data, the excess (integral) molar enthalpy and entropy, H-m(E) and S-m(E), and the IL-IL enthalpic interaction, H-IL-IL(E), were calculated. Using these thermodynamic data, we deduced the mixing schemes, or the "solution structures", of IL-H2O systems. At infinite dilution IL dissociates in H2O, but the subsequent hydration is much weaker than for NaCl. As the concentration of IL increases, [bmim]l ions and the counteranions begin to attract each other up to a threshold mole fraction, x(IL) = 0.015 for [bmim]BF4 and 0.013 for [bmim]l. At still higher mole fractions, IL ions start to organize themselves, directly or in an H2O-Mediated manner. Eventually for x(IL) > 0.5-0.6, IL molecules form clusters of their own kind, as in their pure states. We show tha HI-L-IL, a third derivative of G, provided finer details than H-i(E) and S-i(E) second derivatives, which in turn gave more detailed information than H-m(E) and S-m(E), first derivative quantities.