Multiple ionization and subsequent Coulomb explosion have been studied for many organic molecules and their clusters; however, the metal complexes, particularly the large Coulombic interactions ...expected between a metal and its ligands, have not yet been explored. In this study, the angular distribution of CO+, oxygen, and carbon ions ejected from metal hexacarbonyls (M(CO)6, M: Cr, Mo, W) having O h symmetry by Coulomb explosion in femtosecond laser fields (>1 × 1014 W cm–2) is investigated. The emissions of oxygen ions are well-explained in terms of the geometric alignment along a line inclined 45° relative to the CO–M–CO axis in a M(CO)4 plane. Unlike the explosion behavior of the oxygen ions located on the outer part of the molecule, the explosion behavior of the carbon ions was affected by the laser intensity, kinetic energy, and metal. This finding that the emission trends of carbon sandwiched between oxygen and metal atoms were the opposite of those for oxygen was explained by the obstruction by oxygen, the deformation of structure in bending coordinates, and the strong interaction with charged metal. The anisotropic Coulomb explosion of metal complexes reflecting their structural symmetry and central metal charge is a promising candidate for use in the investigation of large Coulombic interactions at the molecular level.
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•Multiply charged transition metal cations up to 8+ are produced from metallocenes.•Singly charged metal cations liberated from the excited metallocene are further ionized by ...tunneling.•Cations were produced from metallocene at laser intensity lower than that expected by ADK theory for bare metal atoms.
The reactions of a neutral molecule with a singly charged ion in the gas phase have been studied extensively in connection with catalytic reactions, interstellar and planetary atmospheric chemistry, and the MALDI process. In contrast, the reactions of a neutral molecule with a multiply charged ion have rarely been reported, in part because it is difficult to produce such ions in abundance. In this study, we report the production of multiply charged transition metal cations from metallocenes in intense femtosecond laser fields. The most highly charged metals observed at 3 × 1015 W cm−2 are Cr6+, Fe6+, Ni6+, Ru7+, and Os8+. The production of carbon-containing cations originating in cyclopentadienyl ligands is small relative to that of metal cations because the ligands are dominantly liberated as neutral fragments. Metal cations having higher charges are formed by the sequential (stepwise) tunnel ionization of the singly (doubly) charged metal cations that are liberated from the excited metallocene cation (dication). The experimentally measured and theoretically calculated saturation intensities of cation generation are compared. The quasiclassical tunneling theory under a single active electron approximation has been known to underestimate the saturation intensity of singly charged metal cations. However, we investigate that this theory overestimates the saturation intensity of multiply charged metal cations referred to as an enhanced ionization. Moreover, the degree of overestimation becomes significant as the charge number of the metal cation increases. The characteristic deviation of the theoretical predictions from the experimental results is a key issue for the future clarification of the multiple-tunneling ionization processes. We suggest that the polarizabilities depending on the charge number, and presumably the excitation of cations, might be important in the multiple ionization of transition metals. In addition, the production of multiply charged metal cations in abundance, and the reduced production of carbon and hydrocarbon fragment cations achieved by femtosecond laser ionization, will be valuable as sources of multiply charged metal cations for future ion–molecule reaction studies.
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•We performed wet separation of Pd and Mo by using laser-induced particle formation.•We selectively reduced Pd ion by laser and successfully recovered as particles.•Laser condition ...had an influence on recovery efficiency of Pd.•Recovery efficiency and particle size of Pd increased in using pulsed laser.•Laser contributes not only in reduction of Pd ions but also Pd particle growth.
Metal separation by using laser-induced particle formation was applied to the recovery of Pd from a mixed solution with Mo. In this separation, the Pd ions in the mixed solution containing 1vol% ethanol were selectively reduced by irradiation of pulsed laser (10Hz repetition rate) and high-repetition-pulse (HRP) laser (30kHz repetition rate) with the wavelength of 355nm while keeping irradiation power constant. The laser-induced reduction resulted in the generation of the Pd neutrals, which is followed by the aggregation of Pd neutrals in the absence of a stabilizing agent. The generated Pd particles were recovered and separated from the Mo ions by filtration. ICP-AES analysis of the filtrate elucidated that the Pd metals were successfully separated from Mo with a high recovery efficiency (84%). The recovery efficiency of Pd was different in the irradiation between the pulsed and HRP lasers; the efficiency obtained using the pulsed laser was 12% higher than that from the HRP laser. XRD analyses demonstrated that the Pd particles subjected to pulsed laser irradiation were 30 times larger than those subjected to the HRP laser. Based on TEM observations, the sizes of the Pd primary particles were approximately 200nm (pulsed laser) and <10nm (HRP laser). The formation of submicron Pd particles using the pulsed laser increased the recovery efficiency of Pd in this separation, because the Pd particles were recovered by a 0.2μm pore size filter. The formation of different size Pd particles in the irradiation between the pulsed and HRP lasers clearly suggests that the pulsed laser irradiation contributes not only to the reduction of the Pd ion but also to the Pd particle growth in the laser-induced particle formation.
We investigated the formation and fragmentation of multiply charged molecular ions of several aromatic molecules by intense nonresonant femtosecond laser pulses of 1.4 μm with a 130 fs pulse duration ...(up to 2 × 1014 W cm−2). Quadruply charged states were produced for 2,3-benzofluorene and triphenylene molecular ion in large abundance, whereas naphthalene and 1,1′-binaphthyl resulted only in up to triply charged molecular ions. The laser wavelength was nonresonant with regard to the electronic transitions of the neutral molecules, and the degree of fragmentation was strongly correlated with the absorption of the singly charged cation radical. Little fragmentation was observed for naphthalene (off-resonant with cation), whereas heavy fragmentation was observed in the case of 1,1′-binaphthyl (resonant with cation). The degree of H2 (2H) and 2H2 (4H) elimination from molecular ions increased as the charge states increased in all the molecules examined. A striking difference was found between triply and quadruply charged 2,3-benzofluorene: significant suppression of molecular ions with loss of odd number of hydrogen was observed in the quadruply charged ions. The Coulomb explosion of protons in the quadruply charged state and succeeding fragmentation resulted in the formation of triply charged molecular ions with an odd number of hydrogens. The hydrogen elimination mechanism in the highly charged state is discussed.
•Molecular structure determinations by Coulomb explosion imaging are reviewed.•Intact multiply charged molecular cation productions are summarized.•Contribution of electrostatic interactions behind ...the ablation of solid materials is introduced.
Intense femtosecond lasers as well as X-ray free electron lasers provide new means to produce multiply charged molecular cations. The fragmentation processes that these high energy species undergo, termed Coulomb explosion, are utilized to determine the static molecular structures as well as to trace the molecular dynamics of ultrafast chemical reactions. This review focuses on recent advances made in studies of Coulomb explosion imaging, highlighting the use of this process to determine the static structures of complex molecules, geometric isomers, chiral molecules and molecular complexes. Briefly, we summarize the recent time-resolved studies of surface electric fields and the controversy pertaining to the contribution of Coulomb explosion to the mechanism for ablation of solid surfaces.
Quadruply charged, neon-like silicon and helium-like carbon were generated by the exposure of hexamethyldisilane to intense femtosecond laser pulses. Dissociation of the silicon−silicon bond, the ...formation of highly charged silicons, as well as the saturation intensity of their formation were studied by mass spectroscopy. The production of these ions in high abundance, but also with lower laser intensity than theoretically expected for the element, was accomplished by using organosilicon compounds. Multiply charged silicon was generated at low laser intensity because stripping electrons from organosilicon compounds is much easier than from pure silicon due to the loose binding of electrons belonging to molecular orbitals. Femtosecond laser ionization is a valuable methodology for producing highly charged ions in high abundance and is useful in many fields of interest.
To clarify the bereaved family's perceptions about the appropriateness of timing when physicians first referred patients to palliative care units, and to identify the factors contributing to ...family-perceived late referrals.
A multicenter questionnaire survey was conducted on 630 bereaved family members of cancer patents who were admitted to palliative care units in Japan. A total of 318 responses were analyzed (effective response rate, 62%).
Half of the bereaved family members regarded the timing of referrals to palliative care units as late or very late, while less than 5% of families reported early referrals (very late 19%, n = 59, late 30%, n = 96, appropriate 48%, n = 151, early 1.6%, n = 5, and very early 2.2%, n = 7). Multiple regression analyses revealed that the independent determinants of family-perceived late referrals were: family belief before admission that palliative care shortens the patient's life, insufficient in-advance discussion about preferred end-of-life care between patients/families and physicians, families' insufficient preparation for changes of patient conditions, and hospital admission before referrals.
In Japan, the timing of referrals to palliative care units was late or very late from the families' perspectives. The independent determinants of family-perceived late referrals were: family misconception about palliative care, inadequate communication with physicians, and families' insufficient preparation for deterioration of patients' conditions. Systematic strategies to overcome these barriers would contribute to providing appropriate palliative care at all stages of cancer.
Reduction of Yb(III) to Yb(II) by Two-Color Two-Photon Excitation Nakashima, Nobuaki; Yamanaka, Ken-ichi; Yatsuhashi, Tomoyuki
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
09/2013, Letnik:
117, Številka:
35
Journal Article
Recenzirano
Ytterbium 3+ ions in alcohol were found to be reduced to the corresponding 2+ ions upon laser irradiation with a stepwise two-color two-photon excitation. The infrared (975-nm) pulse with a duration ...of 4 ns pumps the ground state to the 4f excited state with the transition of 2F5/2 ← 2F7/2, and the second photon (355-nm) generates the charge transfer (CT) state of Cl 3p to Yb 4f; the reduction then occurs. Laser energy and excitation wavelength dependencies well-explain the above mechanism. The product Yb2+ was detected by its absorption spectrum peak at 367 nm. The absorption spectrum of the intermediate in the two-photon chemistry was measured from the 4f excited state (2F5/2) to the CT state by nanosecond laser photolysis. The intermediate spectrum appears in the wavelengths shorter than 400 nm with the molar extinction coefficient on the order of (102 M–1 cm–1) at 340 nm and can be explained in terms of the CT absorption shifted by IR photon energy. A UV nanosecond laser pulse (266 nm from a YAG laser with a duration of 6 ns) can generate the reactive CT state by one-photon absorption and leads to Yb2+ formation. The reaction yields for single-photon UV excitation and the second photon in the two-photon excitation are on the order of 0.1, suggesting that the reactive states are a common CT state.
Precise separation and purification of f-block elements are important and challenging especially for the reduction of nuclear waste and the recycling of rare metals but are practically difficult ...mainly because of their chemical similarity. A promising way to overcome this difficulty is controlling their oxidation state by nonchemical processes. Here, we show resonance-enhanced multiphoton charge transfer in actinide complexes, which leads to element-specific control of their oxidation states owing to the distinct electronic spectra arising from resonant transitions between f orbitals. We observed oxidation of trivalent americium in nitric acid. In addition, we found that the coordination of nitrates is essential for promoting the oxidation reaction, which is the first finding ever relevant to the primary process of photoexcitation via resonant transitions of f-block elements. The resonance-enhanced photochemical process could be used in the nuclear waste management, as it would facilitate the mutual separation of actinides, such as americium and curium.
Coulomb Explosion of Dichloroethene Geometric Isomers at 1 PW cm–2 Yatsuhashi, Tomoyuki; Nakashima, Nobuaki; Azuma, Juri
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
02/2013, Letnik:
117, Številka:
7
Journal Article
Recenzirano
Strikingly different Coulomb explosion behavior under intense laser fields is shown between the cis and trans geometric isomers of dichloroethene using 40-fs pulses at 0.8 μm. Although the ...fragment-ion distributions in the mass spectra did not aid in the identification of the geometric and positional isomers of the dichloroethenes, we found that the angular distributions of atomic ions were strongly dependent on the geometric structures. The angular distributions of chlorine ions, carbon ions, and protons were similar between 1,1- and cis-1,2-dichloroethene, whereas trans-1,2-dichloroethene showed a very sharp distribution of chlorine ions and quite different distributions of carbon ions and protons. The origin of the anisotropic ion angular distributions is the geometric selection of molecules in the tunnel-ionization process followed by a Coulomb explosion, although molecules are randomly oriented in the gas phase. The highly charged molecular ions exploded into pieces, and the direction of atomic-ion ejection was strongly correlated with the relative configuration of atoms with respect to the electron-extraction axis, the repulsion with adjacent atomic ions within the molecule, and the degree of the persistence of a molecular frame. We propose herein that the most probable electron-extraction axis by tunneling, which is governed by the configuration of molecular orbitals, is different among three dichloroethene isomers. Because multiple ionization under intense laser fields occurs by sequential tunneling processes, the first ionization step at the leading edge of the laser pulse dominates the further ionization steps. Therefore, the shapes of the highest occupied molecular orbitals and probably the underlying orbitals determine the anisotropic emission of atomic ions that can be used to identify isomers.
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