Multiphoton dissociation and ionization of nickelocene

In this paper we report the results of an experimental study of collision-free molecular multiphoton dissociation (MPD) and molecular multiphoton ionization (MPI) of nickelocene (NiC₁₀H₁₀), induced by the light of a tunable dye laser in the wavelength region 3750–5200 A. The spectral dependence of the ion signal reveals a multitude of narrow (fwhm from <0.5 cm^?1 to 1.5 cm^?1) intense peaks superimposed on a very weak background (relative amplitude ratio for peaks/background ≈ 10³). The sharp resonances in the ion signal are attributed, on the basis of spectroscopic analysis, to two-photon resonant three-photon ionization of Ni(I) and to one-photon resonant three-photon ionization of Ni(I), the Ni(I) being produced by MPD of nickelocene. The ion signal in the spectral range 3750–3950 A reveals enhanced continuous background due to MPI of nickelocene. This ion signal spectra, together with studies of the intensity dependence of the overall (nickelocene MPD) - (Ni(I) MPI) processes, as well as the (nickelocene molecular MPI) reaction, reveal four reactive processes. (a) Two-photon molecular MPI for hω ? 3.10 eV photons. (b) Three-photon molecular MPI for hω = 3.10-2.10 eV. (c) Two-photon MPD at hω ? 2.86 eV. (d) Three-photon MPD for hω = 2.8-1.9 eV. The overall dissociation energy of nickelocene (Nicp₂) to give Ni + 2cp was determined to be 5.76 ± 0.60 eV and the two-photon ionization potential of this molecule is 6.29 ± 0.015 eV. Our results provide dynamic evidence concerning a simultaneous “explosive” photodissociation mechanism of Nicp₂ by process (c) and for the dominating role of the dissociative channel, characterized by a branching ratio of ?50 in favor of predissociation over autoionization, for process (c) at 6.3–6.6 eV. The MPD processes (c) and (d) are expected to exhibit intramolecular erosion of phase coherence effects. Processes (c) and (d) are of high efficiency ≈0.01 ions/molecule at saturation exhibited at laser power of ≈ 10⁸ W cm^?2.     

Low energy,variable angle electron-impact excitation of 1,3,5-hexatriene

A mixture of cis and trans 1,3,5-hexatriene has been studied by electron impact at incident electron energies of 20 eV, 40 eV, 50 eV, and 70 eV, at scattering angles from 0° to 80°, and with effective energy resolutions in the range from 0.05 eV to 0.15 eV. Singlet → triplet transitions with maximum intensities at 2.61 eV and 4.11 eV are observed. The lowest energy spin-allowed excitation which can be detected is the electric dipole-allowed $\text{X}$¹ A_g → 1 ¹B_u transition (in the notation appropriate for the trans isomer). No evidence has been found for a spin-allowed but symmetry-forbidden $\text{X}$¹ A_g → 2 ¹A_g excitation in the vicinity of 4.4 eV transition energy. Many other spin-allowed excitations are observed in the 6–11 eV energy-loss region, and the correlation between these features and those observed in high resolution ultraviolet absorption spectra and other electron-impact spectra is discussed.     

The A′ 3Π(2u-X 1Σg+ emission spectrum of Br2 in an argon matrix

The emission spectrum of the A′ ³Π(2_u)-X ¹Σ_g⁺ system of Br₂ in an argon matrix is reported. The vibrationally resolved spectra have been analysed and two possible vibrational numberings have been determined. These provide estimates for T_c of 12966 ± 8 and 12679 ± 8 cm⁻¹, respectively. Excitation spectra have been examined, and these provide insight into the excitation and relaxation mechanisms present in the matrix.     

Measurements of differential cross sections for vibrational quantum transitions in scattering of Li+ on H2

A pulsed monoenergetic ⁷Li⁺ ion beam (lab. energy 10–40 eV) is scattered from a highly collimated (= 1.5°) H₂ nozzle beam. The time-of-flight spectrum of the ions scattered in the forward laboratory direction shows both a fast peak corresponding to forward center-of-mass scattering and a slow peak corresponding to wide-angle center-of-mass scattering. These peaks have been further resolved to show contributions from individual vibrational quantum transitions. From an analysis of the time-of flight spectra the differential inelastic cross sections for a wide range of angles and energies between 2 eV <E_cm < 9 eV have been determined. The spectra also contain information on rotational inelastic cross sections.     

Electrical conduction of bis(1,2-diondioximato)metals(II) and their partially oxidized complexes at high pressures

The resistivity of one-dimensional d⁸-metal complexes with various kinds of 1,2-diondioxime(dimethylglyoxime, nioxime, and diphenylglyoxime) ligands has been measured at high pressures. The resistivity of M(dmg)₂ and M(niox)₂ decreased with increasing pressure. The resistivity of M(dmg)₂ is much lower than that of M(niox)₂ at high pressure, though M-M distances and optical energy gaps in both salts are almost the same at atmospheric pressure. An anomalous low resistivity has been observed in Pt(dmg)₂ at about 40 kbar. The electrical resistivity of M(niox)₂ and M(dmg)₂, oxidized by oxidizing agents, decreased with increasing pressure. The resistivity of partially oxidized Pt complexes is significantly higher than that of the parent compounds at high pressure. On the contrary, partially oxidized Ni and Pd complexes are more conductive than unoxidized compounds at high pressures. The electrocal resistivity of unoxidized and partially oxidized Pt complexes increased with increasing pressure at higher pressures. The resistivity minimum at high pressure has been observed only in Pt complexes. The infrared spectra of the d⁸-metal complexes and their partially oxidized complexes have been investigated. The frequency of the CN stretching vibration in M(dmg)₂ and M(niox)₂ salts increases in the order Ni > Pd > Pt; on the other hand, the frequency of M(niox)₂X_n increases in the order Ni < Pd < Pt. The frequency of the CN stretching vibration is closely related to the effect of metal-ligand π1 back bonding in d⁸-metal complexes. Some anomalies in the resistance-pressure curve have been found in Ni(dpg)₂, Ni(dpg)₂I, Ni(dpg)₂I_0.5, and Ni(dpg)₂I_0.14. The anomalies are explained by new pressure-induced phase transitions.     

Microwave spectra in the v8 and 2v8 states of methyl isocyanide and its 15N derivative

A new analysis of the microwave spectra of methyl isocyanide CH₃¹⁴NC in the v₈ and 2v₈ states is obtained by the use of more experimental data and calculations by diagonalization of the energy matrix. The same spectra for the ¹⁵N derivative have been observed, and their analysis reveals resonant effects still stronger than for CH₃¹⁴NC. Sets of rotation and rotation-vibration constants are reported for both molecules.     

Absorption spectroscopy of size-selected trimers and pentamers transition metal clusters isolated in rare gas solids: preliminary steps

Size-selected positive ionic silver trimers and pentamers and nickel trimers have been codeposited, at low kinetic energy, with rare gas (Kr) onto a cold transparent surface. They have been neutralized onto the surface by electrons of few eV, with an efficiency of 80±20%. The optical absorption spectra of the resulting matrix-isolated neutral species have been recorded, with good sensitivity, in the UV-visible range. The evaporation of clusters, detected on the atom signal after deposition of Ni trimers of 20 eV, neutralized by electrons of 5 eV, is shown to be roughly 20%. This indicates that Ni₃ clusters are present in the matrix but their number is actually too low to be optically detected.     

Doubly charged ion mass spectra: III—N-alkanes

Doubly charged ion mass spectra have been obtained for 15 n-alkane hydrocarbons. Spectra were measured using a Nier-Johnson geometry Hitachi RMU-7L mass spectrometer operated at 1.6kV accelerating voltage. Fragment ions, which resulted from C? C bond rupture and extensive H loss, dominated the spectra. Molecular ions have not been observed. The most intense ions in the doubly charged ion mass spectra of n-alkanes were [C₂H₄]²⁺, [C₃H₂]²⁺, [C₄H₃]²⁺, [C₅H₂]²⁺, [C₆H₆]²⁺, [C₆H₈]²⁺, [C₇H₆]²⁺, [C₇H₈]²⁺, [C₈H₆]²⁺ and [C₈H₈]²⁺. Appearance energies for forming the prominent doubly charged fragment ions have been measured and range from 27.5 eV to energies greater than 60eV. A geometry optimized SCF approach has been used to compute the energies and structures of prominent ions in the doubly charged mass spectra.     

High resolution core level photoelectron spectroscopy using He II radiation: electric field gradient splittings in group IIB and group III compounds

Using a charged particle oscillator He II discharge lamp, we have obtained high resolution 40.8 cV photoelectron spectra of the 3d core levels of Zn and Ga in Me₂Zn and Me₃Ga respectively, and the Pb 5d core levels in Et₄Pb. The overall instrumental resolution is between 25 meV and 40 meV for all spectra. Inherent core level widths for the Zn 3d (?0.025 eV), Ga 3d (?0.15 eV) and Pb 5d (?0.32 eV) energy levels have been obtained from these spectra. The Me₂Zn and Me₃Ga spectra consists of five peaks due to the combined effects of spin orbit coupling and large non-cubic ligand fields (the C⁰₂ term in the crystal field expansion). In contrast, the Et₄Pb 5d spectrum shows no appreciable ligand field splitting, as expected for a tetrahedral molecule.     

Structural,thermal, and optical properties of Pr3+/Yb3+ co-doped oxyhalide tellurite glasses and its nano-crystalline parts

Nano-crystalized glass-ceramics and ceramics co-doped with Pr³⁺/Yb³⁺ have been successfully prepared by heat treatment of the precursor oxyhalide glass sample synthesized by melt-quench method. Thermal measurement of glass sample shows its glass transition temperature (T_g), and onset crystallization temperature (T_c). Formation of nano-crystals was verified by X-ray diffraction patterns and transmission electron microscopy (TEM) images. Values of optical band gap (E_opt) were found to be 2.85 eV and 1.54 eV for direct and indirect transitions, respectively. Up and downconversion emission spectra recorded with 976 and 532 nm laser wavelengths show emission from Pr³⁺ ions. Emission of Pr³⁺ enhances approximately thirty times when Yb³⁺ ion is added with the matrix. The Stark splitting and the intensity of different emission bands increase effectively when we approach to ceramic via glass-ceramic sample. Intense upconversion emission observed by naked eyes has been quantified in terms of standard chromaticity diagram (CIE). Power dependence study shows that the upconversion of NIR radiation to visible takes place mainly via photon avalanche (PA) process. Upconversion mechanisms have been discussed in terms of excited state absorption (ESA) and energy transfer (ET) processes.     

Oxygen solubility in liquid nickel containing zirconium

The solubility of oxygen in liquid nickel containing zirconium at 1873 K has been experimentally studied for the first time. It has been shown that zirconium is a rather strong deoxidizing agent in liquid nickel. The equilibrium constant of the reaction of zirconium and oxygen dissolved in liquid nickel (logK_(1)(Ni) =–6.788), the interaction parameters characterizing these solutions (e_Zr(Ni)^O =–2.01; e_O(Ni)^Zr =–0.35; e_Zr(Ni)^Zr = 0.24), and the activity coefficient of zirconium in nickel at infinite dilution (γ_Zr(Ni)^o = 1.03 × 10^–8) have been determined. The zirconium content at the minimum of the oxygen solubility curve and the corresponding oxygen concentration have been determined.     

Production and properties of CO2 cluster anions

Stoichiometric and non-stoichiometric negatively charged CO₂ cluster ions have been produced in a crossed neutral cluster/electron beam ion source. The abundance and stability of these ions have been studied with a double focussing sector field mass spectrometer. The observed abundance anomalies (“magic numbers”) in the mass spectra of (CO₂) _n ^? and (CO₂) _n O^? ions correlate with corresponding small and large metastable fractions of these ions (for loss of one CO₂ unit). Variation of the measured metastable fractions as a function ofn are related to corresponding changes in the monomer binding energies. In addition, we have observed for the first time (CO₂) _n O ₂ ^? ions (i.e. at electron energies above 8 eV with an energy resonance at about 14 eV) and we discuss possible production mechanisms for these ions. Relative electron attachment cross sections have been determined in the energy regime O<E≦20 eV for (CO₂) _n ^? , (CO₂) _n O^? and (CO₂) _n O ₂ ^? withn=1 to 20. The shape of the cross section function for (CO₂) _n O^? is strongly dependent on the cluster sizen.     

Observation of resonance effects in the relative partial photoionization cross sections of the d bands of M(CO)6, M = Cr,Mo and W

Relative partial photoionization cross sections as a function of photon energy, over the range 20–110 eV, have been measured for the valence bands of Cr(CO)₆, Mo(CO)₆ and W(CO)₆. All three t_2g⁻¹ bands show a very pronounced increase in intensity at photon energies (hv) corresponding to np resonant absorption (Cr(CO)₆, hv = 52.5 eV, n = 3; Mo(CO)₆,hv = 48 eV, n = 4; W(CO)₆, hv = 44 and 53 eV, n = 5). The other valence bands show a small intensity increase at similar energies. Observation of such resonant photoemission provides an unambiguous method for assignment of nd bands in the photoelectron spectra of gas-phase molecules.     

Heteropoly compounds as octahedral high valence complex. Spectrochemical properties of Waugh-structure enneamolybdonickelate(IV) and enneamolybdomanganate(IV) ions

Electronic absorption and magnetic circular dichroism (MCD) spectra in UV-vis region of Waugh-structure [XMo₉O₃₂]^6?(X = Ni(IV), Mn(IV)) ion in aqueous solution and solid IR spectra have been measured. The Ni(IV) ion in the polyanion has a low-spin d⁶ electronic configuration and the Mn(IV) ion has a d³ configuration. Visible absorption spectrum of the nickelate(IV) polyanion is interpreted to be mainly governed by charge-transfer transitions of the “ligand”, Mo₉O₃₂, to Ni(IV) ion, rather than d-d transitions, while visible absorption of the manganate(IV) polyanion is governed, to a great extent, by d-d transitions. It is indicated by the MCD spectrum that the splitting of the first d-d absorption in the manganate(IV) polyanion is due to a contribution of the spin-forbiden transition, rather than from a trigonal splitting of the spin-allowed transition. Absorption and MCD spectra in UV region are due to charge-transfer transition within a common “ligand”, which are less influenced by the kind of heteroatom, Ni(IV) or Mn(IV). The MCD pattern by the intra-ligand charge-transfer is especially characteristic of the Waugh-structure polyanions.     

Perturbations of molecular extravalence excitations by rare-gas fluids

In this paper we report the results of an experimental study of the vacuum ultraviolet absorption spectra of molecular impurity states of methyl iodide in Ar (density range ? = 0–1.4 g cm^?3) and in Kr (? = 0–2.3 g cm^?3), of carbon disulphide in Ar (? = 0–1.4 g cm^?3) and of formaldehyde in Ar (? = 0–1.25 g cm^?3). The experimental results provide new information regarding medium perturbations of intravalenc transitions, of the lowest extravalence transitions and of transitions to mixed valence—Rydberg configurations, which serve as a diagnostic tool to distinguish between different types of electronic excitations. All the lowest extravalence molecular excitations exhibit appreciable blue spectral shifts at moderate and at high fluid densities, intravalence transitions are practically insensitive to medium effects, while excitations to mixed valence—Rydberg configurations are characterized by a moderate blue spectral shift. New information has been obtained concerning the energetics of molecular ionization processes in a dense fluid. The high n = 2–5 Rydberg states of CH₃l exhibit a large red shift at moderate (? = 0–0.5 cm^?3) Ar densities. The ionization potential E_g and the effective Rydberg constant G for CH₃I in Ar was found to decrease from G = 13.6 eV and E_g = 9.55 eV at ? = 0 and E_g = 9.08 eV and constant G for CH₃l in Ar was found to decrease from G = 13.6 eV and E_g = 9.55eV at ? = 0 and E_g = 9.08 eV and G ≈ 7.15 eV at ? = 0.5 g cm^?3. Experimental evidence was obtained for the identification of n = 2 molecular Wannier impurity states of CH₃I and of CH₂O in liquid Ar. These spectroscopic data result in E_g ≈ 8.6 eV for CH₃I in liquid Ar and E_g ≈ 10.2 eV for CH₂O in liquid Ar.     

Optical transitions,XPS, electronic states in NiPS3

We have measured the optical absorption below the fundamental threshold, the normal-incidence reflectivity between 1.5 and 30 eV and the X-ray photoemission spectra of NiPS₃. Shake-up satellites present at the Ni 2p and 3p core levels are strong evidence for the ionicity of the NiS bonds. We have also derived a qualitative molecular orbital model of NiPS₃ in which the trigonal crystal field splits the P and S 3p_xp_y-3p_a states, and strong covalent hybridization between P and S p_xp_y orbitals leads to covalent electronic bonding. Ni is envisaged as a divalent ion which plays little role in the electronic bonding and its 3d levels are localized, lying near the top both of the valence states. This model accounts well for both the valence band XPS data and the low energy optical transitions. Our model should represent, at the center of the Brillouin zone but not at the boundaries, the energy level sequence in NiPS₃ and other related MPX₃ layer-type compounds where M Co²⁺, Mn²⁺, Fe²⁺, Zn²⁺ and X is sulfur or selenium.The XPS spectra and optical properties of NiPS₃ have been obtained and interpreted on a qualitative molecular orbital model in which the Ni is a divalent positive ion which plays little role in the bonding. Evidence for such ionicity appears in the optical properties and XPS satellite structures, as well as in the magnetic properties. The model should represent qualitatively the band structure at the center of the Brillouin zone, but not at the boundaries. It should also be valid for other compounds similar to NiPS₃, i.e. those with other metals in place of Ni and those with Se in place of S.     

The infrared spectra of ethylenediamine complexes—II. Tris-, bis- and mono(ethylenediamine) complexes of metal(II) halides

The i.r. spectra of the complexes M(en)₃X₂ (M = Mn, Fe, Co, Ni, Cu, Zn), trans-Cu(en)₂X₂, Ni(en)₂X₂ and M(en)X₂ (M = Ni, Cu, Zn; X = Cl, Br, I) have been studied. Assignments are proposed for the tris(ethylenediamine) complexes on the basis of ¹⁵N-, N₂D₄- and C₂D₄-labelling of en and the effects of metal ion substitution in relation to our earlier study of [M(en)₃]SO₄ complexes. Assignments for the bis(ethylenediamine) complexes are based on our observations of halogen-sensitivity and earlier studies on metal isotope labelling and ligand deuteration of the halide complexes and a normal coordinate analysis of the [Cu(en)₂]²⁺ species. The spectra of the halide complexes have been extended below 200 cm⁻¹ for the first time. Finally, the spectra of the mono(ethylenediamine) complexes are discussed in relation to their known or probable structures.     

Spectroscopy and stereochemistry of the optically active copper(II), cobalt(II) and nickel(II) complexes with Schiff bases N,N′-(1R,2R)-(−)-1,2-cyclohexylenebis(3-methylbenzylideneiminato) and N,N′-(1R,2R)-(−)-1,2-cyclohexylenebis(5-methylbenzylideneiminato)

Schiff bases obtained from N,N′-(1R,2R)-1,2-cyclohexanediamine and 2-hydroxy-3-methylbenzaldehyde, 2-hydroxy-5-methylbenzaldehyde, have been used as ligands for copper(II), cobalt(II) and nickel(II). The complexes were characterized with UV–Vis, circular dichroism (CD), infrared, diamagnetic and paramagnetic ¹H NMR spectroscopy. CD spectra revealed exciton coupled π→π* transitions. Assignments of LMCT and d–d transitions in CD spectra of Ni(II), Co(II) and Cu(II) complexes is proposed. CD data are characteristic for central ion tetrahedral distortion from the planarity and λ conformation of the cyclohexane ring. ¹H NMR of Ni(II) complexes exhibited significant coordination shifts of CHN and ring protons which are in the closest proximity to Ni(II). The ¹H NMR paramagnetic spectra of Co(II) complexes revealed the most upfield shifted resonance at −60 ppm assigned to CHN and −28 ppm to hydrogen atom at C(5′) of the phenyl ring. Results of spectral analyses suggest central ions in a distorted square-planar geometry with N₂O₂ chromofore group.     

Anagostic interactions, revisiting the crystal structure of nickel dithiocarbamate complex and its antibacterial and antifungal studies

The synthesis of Ni(dtc)₂ [dtc = diethyldithiocarbamate] has been achieved by the interaction of NiL(ClO₄)₂ with sodium diethyldithiocarbamate. Although single crystal structure of this complex was already reported (R = 10.6%), we were able to refine crystal structure up to R = 2.99%. We also observed rare C-H?Ni anagostic interactions generally exhibited by d⁸ complexes which were overlooked previously. To investigate the structure of Ni(dtc)₂ in solution, variable temperature NMR spectra in solution have also been recorded between 25 and −50 °C. Ni(dtc)₂ was also tested for antibacterial and antifungal activities. It showed higher activity against the bacteria and fungi than the known antibiotics.     

Synthesis, spectral and thermal studies of N,N − -pyridine-2,6-diyl bis[N −-phenyl(thiourea)] and its metal complexes

Four new metal complexes with the general formula, [ML·mH₂O]nH₂O (where, M = Cu(I), Co(II), Ni(II) or Zn(II); L = N,N ^?-pyridine–2,6-diyl bis[N ^?-phenyl (thiourea)] (PDPT); m = 1 or 3 and n = 0.5 or 4.0), have been synthesized and characterized by elemental analyses, spectral analyses (IR, UV–Vis., ¹H-NMR and MS), thermal analyses (TGA), conductivity and magnetic measurements. The results showed that the ligand (PDPT) acts in a mononegative tridentate manner towards Cu(I) ion coordinating via the two thiol sulfurs and pyridyl nitrogen groups with displacement of only one hydrogen atom from the thiol group, while the ligand behaves in a binegative tridentate manner towards the Co(II), Ni(II) and Zn(II) ions with displacement of two hydrogen atoms from the two thiol groups. The value of magnetic measurements showed a diamagnetic character of the copper complex indicating the reduction of Cu(II) to Cu(I). Semi-empirical calculations of the ligand and its metal complexes have been used to study the molecular geometry using ZINDO/1, PM3 and AM1. Also, the harmonic vibration spectra of the ligand and its metal complexes have been investigated with the purpose to assist the experimental assignment of metal complexes. The results of the optical absorption studies reveal that the optical transition is direct with band gaps energy (E_g) values 2.62, 1.98 and 1.85 eV for Cu, Co and Ni complexes, respectively, indicating that these complexes can behave as semi-conductors.