Highly sensitive detection of sodium in aqueous solutions using laser-induced breakdown spectroscopy with liquid sheet jets.

Laser-induced breakdown spectroscopy (LIBS) combined with liquid jets was applied to the detection of trace sodium (Na) in aqueous solutions. The sensitivities of two types of liquid jets were compared: a liquid cylindrical jet with a diameter of 500 µm and a liquid sheet jet with a thickness of 20 µm. Compared with the cylindrical jet, the liquid sheet jet effectively reduced the splash from the laser-irradiated surface and produced long-lived luminous plasma. The limit of detection (LOD) of Na was determined to be 0.57 µg/L for the sheet jet and 10.5 µg/L for the cylindrical jet. The LOD obtained for the sheet jet was comparable to those obtained for commercially available inductively coupled plasma emission spectrometers.

Application of an Augmentation Method to MCR-ALS Analysis for XAFS and Raman Data Matrices in the Structural Change of Isopolymolybdates.

We measured X-ray absorption fine structure (XAFS) and Raman spectra of isopolymolybdates(VI) in highly concentrated HNO3 solution (0.15 - 4.0 M), which change their geometries depending on the acid concentration, and performed the simultaneous resolution of the XAFS and Raman data using a multivariate curve resolution by alternating least-squares (MCR-ALS) analysis. In iterative ALS optimization, initial data matrices were prepared by two different methods. For low sensitivity of the XAFS spectra to the geometrical change of the isopolymolybdates, the MCR-ALS result of single XAFS data matrix shows a large dependence on the preparation method of the initial data matrices. This problem is improved by the simultaneous resolution of the XAFS and Raman data: the MCR-ALS result of an augmented matrix of these data has little dependence on the initial data matrices. This indicates that the augmentation method effectively improves the rotation ambiguities in the MCR-ALS analysis of the XAFS data.

Photoelectron Spectroscopy of Molecular Anion of Alq3: An Estimation of Reorganization Energy for Electron Transport in the Bulk.

A molecular anion of tris(8-hydroxyquinolinato)aluminum (Alq3) was generated by a pulsed discharge to the solid sample under supersonic expansion and its photoelectron spectrum was recorded after mass selection. The vertical detachment energy of Alq3 - and the adiabatic electron affinity of Alq3 were determined to be 1.24 ± 0.01 and 0.89 ± 0.04 eV, respectively. By using these energies determined for monomeric Alq3, the reorganization energy for the intermolecular electron transport in bulk Alq3 was estimated to be 0.70 ± 0.08 eV.

Anion photoelectron spectroscopy of free [Au25(SC12H25)18].

Previous theoretical studies have shown that the thiolated gold cluster compound [Au25(SR)18]- can be viewed as a prototypical superatom with a closed electronic structure. The quantized electronic structure of [Au25(SR)18]- has been experimentally demonstrated by optical and electrochemical methods in the dispersed state. Nevertheless, no direct information is available on the energy levels and densities of occupied states. Here, we report the photoelectron spectrum of [Au25(SC12H25)18]- isolated under vacuum for the first time. The spectrum exhibits two distinct peaks, corresponding to electron detachment from the superatomic 1P orbitals and Au 5d orbitals of the Au13 core. The adiabatic electron affinity of [Au25(SC12H25)18]0 was experimentally determined to be 2.2 eV, which is significantly smaller than that of [Au25(SCH3)18]0 predicted theoretically.

Photoelectron Spectroscopy and Ab Initio Calculations of CS3(-) Isomers: Carbon Trisulfide and Carbon Disulfide S-Sulfide Anions.

Carbon sulfides are known as a class of binary compounds that can exist in various isomeric and/or polymeric forms. As for a sulfur-rich compound with the composition formula CS3, two possible constitutional isomers have been proposed experimentally or theoretically for the neutral species and its corresponding radical cation and anion. Although the previous studies claim that one isomer has a carbon trisulfide (CS3) C-centered configuration and the other has a carbon disulfide S-sulfide (SCSS) chain configuration, they have not yet been fully identified by a spectroscopic method. In this study, we have prepared the anions of those isomers in the gas phase by employing two types of reactions: dissociative electron attachment to 1,3-dithiole-2-thione for CS3(-) formation and the S(-) + CS2 ion-molecule reaction for SCSS(-). Photoelectron spectroscopic measurements reveal that the reactions result in the production of two anionic species that can be well distinguished by their vertical detachment energy. With the aid of ab initio calculations, they are identified distinctively as the anions of carbon trisulfide and carbon disulfide S-sulfide.

Incorporation of ROH (R = CH3, C2H5, 2-C3H7) into (H2O)6(-): substituent effect on the growth process of the hydrogen-bond network.

The condensation reaction of water cluster anions, (H2O)n(-) + H2O → (H2O)n+1(-), offers a prime opportunity to explore the growth process of the hydrogen-bond network involving molecular uptake and network rearrangement. Here, by exploiting an Ar-mediated approach, we investigate the association reaction of water hexamer anions, (H2O)6(-), with ROH (R = CH3, C2H5, 2-C3H7) by mass spectrometry combined with photoelectron spectroscopy. Quantitative analysis of the product mass spectra reveals that incorporation of ROH (R = CH3, C2H5) into (H2O)6(-) occurs with a cross section of the same size as in the (H2O)6(-) + D2O condensation, but with a slightly smaller cross section for R = 2-C3H7. Coexistence of two types of isomers, high electron-binding (type I) and low electron-binding (type II) forms, is observed in all the product ROH·(H2O)6(-) species by photoelectron spectroscopic measurement. These findings, in conjunction with ab initio study of MeOH·(H2O)6(-) structures, lead us to propose a molecular uptake mechanism at play in the incorporation of ROH into the (H2O)6(-) network. This also provides complementary information on the homogeneous condensation process of pure water cluster anions.

Hydrogen-Bond Network Transformation in Water-Cluster Anions Induced by the Complex Formation with Benzene.

We report spectroscopic evidence of isomer interconversion in water cluster anions, (H2O)n(-), which occurs through the interaction with a benzene molecule. An anion complex composed of (H2O)6(-) and benzene, Bz·(H2O)6(-), is formed via the reaction of (H2O)6(-)Arm with benzene. The reaction proceeds as an Ar-mediated association process such that a rapid energy dissipation by sequential Ar evaporation efficiently suppresses the thermionic emission of e(-), H2O, or both, giving rise to the formation of Bz·(H2O)6(-). Photoelectron spectroscopy is employed to probe the electronic properties of the anionic species, which reveals that "type I → type II" isomer interconversion proceeds in the (H2O)6(-) moiety during the formation of Bz·(H2O)6(-). With the aid of ab initio calculations, we conclude that the interconversion is driven by preferential stabilization of the H-bond network of type II arrangement through the formation of a nonconventional O-H···π hydrogen bond between (H2O)6(-) and Bz.

Theoretical study on the excess electron binding mechanism in the [CH(3)NO(2).(H(2)O)(n)](-) (n = 1-6) anion clusters.

The excess electron binding mechanism of the anionic nitromethane-water clusters was theoretically investigated using the potential energy surfaces calculated by high-level electronic structure theories. The mechanism was first studied for the dipole-bound and valence-bound anionic states of the CH(3)NO(2)(-) monomer with the ab initio multireference configuration interaction method to reveal the electron transformation process between these anionic states in detail. As a result, it was found that both the NO(2) tilting angle and NO distances play an essential role in this electron transformation. Following this result, various water solvation structures of the valence-bound CH(3)NO(2)(-) anion were optimized with up to six water solvents using the second-order Møller-Plesset (MP2) method. The calculated results predicted that the vertical detachment energy of the valence-bound CH(3)NO(2)(-) anion increases gradually with the hydration number, as is consistent with recent experimental observations. We also investigated metastable complexes composed of CH(3)NO(2) and (H(2)O)(6)(-) by using the MP2 and long-range corrected density functional theory calculations. Two types of dipole-bound forms were obtained for the [CH(3)NO(2).(H(2)O)(6)] anion complex. In one form the excess electron is internally suspended between the two moieties while in the other form two dipolar moieties are cooperatively arranged to reinforce the electron-dipole interaction.

Photoelectron spectroscopy and Ab initio calculations of peroxy form of SO(4)(-) anion.

A photoelectron spectrum is reported for gas-phase SO(4)(-) formed in an electron-impact ionized free jet of SO(2)(1%)/O(2)(10%)/Ar. The vertical detachment energy (VDE) of the SO(4)(-) species is determined to be 3.78 +/- 0.02 eV, which is significantly smaller than the VDE value reported for the sulfur-centered form of SO(4)(-) extracted from an Na(2)S(2)O(8) solution. With the aid of MP2/6-311+G(2df) calculations, the newly formed species is identified as a peroxy form of SO(4)(-), which is well described as OOSO(2)(-)(C(1), (2)A) having an S-O linkage between the O(2) and SO(2) units. The electronic properties of OOSO(2)(-) are characterized by the singly occupied molecular orbital (SOMO) constructed by an out-of-phase superposition of the 1a(2) orbital of SO(2) and the half-filled 2ppi(g)* of O(2)(-). On the basis of these findings, a possible formation mechanism of OOSO(2)(-) is discussed in terms of a "solvent-mediated" addition reaction, where O(2)(-) stabilized by solvation attacks SO(2) while retaining the 2ppi(g)* excess electron.

Formation and photodestruction of dual dipole-bound anion (H(2)O)(6){e(-)}CH(3)NO(2).

A new type of dipole-bound anion composed of water and nitromethane (CH(3)NO(2)) is formed via the incorporation of CH(3)NO(2) into argon-solvated water hexamer anions, (H(2)O)(6) (-)Ar(m). The reaction proceeds as an Ar-mediated process such that an effective energy dissipation through sequential Ar evaporation gives rise to the formation of [CH(3)NO(2)(H(2)O)(6)](-). Photoelectron spectroscopy is employed to probe the electronic properties of the [CH(3)NO(2)(H(2)O)(6)](-) anion, which reveals that the dipole-bound nature of (H(2)O)(6) (-) remains almost intact in the product anion; the vertical detachment energy of [CH(3)NO(2)(H(2)O)(6)](-) is determined to be 0.65+/-0.02 eV. This spectroscopic finding, together with other suggestive evidences, allows us to refer to [CH(3)NO(2)(H(2)O)(6)](-) as a dual dipole-bound anion described as (H(2)O)(6){e(-)}CH(3)NO(2), where the diffuse excess electron interacts with both the (H(2)O)(6) and CH(3)NO(2) moieties via the electron-dipole interactions. The photodestruction of (H(2)O)(6){e(-)}CH(3)NO(2) at 2134 nm (0.58 eV) occurs with a competition between electron detachment and fragmentation. The latter leads exclusively to the formation of CH(3)NO(2) (-)(H(2)O)(3), indicating that the dual dipole-bound anion serves as a precursor to the hydrated valence anion of CH(3)NO(2).

Photodissociation of gas-phase I3-: comprehensive understanding of nonadiabatic dissociation dynamics.

Photodissociation of the gas-phase tri-iodide anion, I3-, was investigated using photofragment time of flight (TOF) mass spectrometry combined with the core extraction method. An analysis of the TOF profiles provided the kinetic energy and angular distributions of photofragment ions and photoneutrals, from which the photoproduct branching fractions were determined in the excitation energy range of 3.26-4.27 eV. The measurement has revealed that (1) in the entire energy range investigated, three-body dissociation occurs preferentially as the "charge-asymmetric" process I-(1S)+I(2P3/2)+I(2P3/2) with the yield of approximately 30%-40%, where the excess charge is localized on the end atoms of the dissociating I3-, and that (2) two-body dissociation via the 3Piu(0u+)<--1Sigmag+(0g+) excitation proceeds as I-(1S)+I2(X 1Sigmag+)/I2(A 3Pi1u) or I(2P3/2)+I2-(X 2Sigmau+) with the yield of approximately 60%, while that via the 1Sigmau+(0u+)<--1Sigmag+(0g+) excitation alternatively as I*(2P1/2)+I2-(X 2Sigmau+) or I-(1S)+I2(B 3Piu) with the yield of approximately 60%. Ab initio calculations including spin-orbit configuration interactions were also performed to gain precise information on the potential energy surfaces relevant to the I3- photodissociation. The calculations have shown the presence of conical intersections and avoided crossings located along the symmetric stretch coordinate near the ground-state equilibrium geometry of I3-, which play key roles for the two-body and the three-body product branching. The nonadiabatic nature of the I3- photodissociation dynamics is discussed by combining the experimental findings and the ab initio results.