A novel chemical ionization reagent ion for organic analytes: the aquachloromanganese(II) cation [ClMn(H2O)+]

The reactivity of ClMn(H₂O)⁺ towards small organic compounds (L) was examined in a Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometer. The organic compounds studied are aliphatic and aromatic alcohols, aliphatic amines, ketones, an epoxide, an ether, a thiol and a phosphine. All the reactions lead to the formation of the ClMn(H₂O)(L)⁺ complex, which dissociates by loss of the H₂O molecule. In general, the reactions were found to occur with high efficiencies (>85%), indicating them to be exothermic. Electron transfer was also observed between ClMn(H₂O)⁺ and compounds with low ionization energies (IE), to form the molecular ion (L^+?) of the analyte. Based on these observations, the IE of ClMn(H₂O)⁺ is approximated to be 8.1 ± 0.1 eV. Thus, the utility of ClMn(H₂O)⁺ as a chemical ionization reagent in mass spectrometry is expected to be limited to organic compounds with IEs greater than 8 eV. Copyright © 2012 John Wiley & Sons, Ltd.     

Skin Bond Electron Relaxation Dynamics of Germanium Manipulated by Interactions with H2, O2, H2O,H2O2, HF,and Au

Although germanium performs amazingly well at sites surrounding hetero‐coordinated impurities and under‐coordinated defects or skins with unusual properties, having important impact on electronic and optical devices, understanding the behavior of the local bonds and electrons at such sites remains a great challenge. Here we show that a combination of density functional theory calculations, zone‐resolved X‐ray photoelectron spectroscopy, and bond order length strength correlation mechanism has enabled us to clarify the physical origin of the Ge 3d core‐level shift for the under‐coordinated (111) and (100) skin with and without hetero‐coordinated H₂, O₂, H₂O, H₂O₂, HF impurities. The Ge 3d level shifts from 27.579 (for an isolated atom) by 1.381 to 28.960 eV upon bulk formation. Atomic under‐coordination shifts the binding energy further to 29.823 eV for the (001) and to 29.713 eV for the (111) monolayer skin. Addition of O₂, HF, H₂O, H₂O₂ and Au impurities results in quantum entrapment by different amounts, but H adsorption leads to polarization.     

Structure of water (H2O) 6 − and ammonium (NH3) 13 − clusters with an excess electron: Quantum chemical studies

The B3LYP method within DFT and the ab initio MP2 method with an extended 6-311++G(3df,3pd) basis set are employed to calculate the adiabatic bound state of an excess electron in (H₂O) ₆ ^? water and (NH₃) ₁₃ ^? . ammonium clusters. Adiabatic electron affinity of (H₂O)₆ and (NH₃)₁₃ clusters is 0.03–0.18 eV and 0.18 eV respectively. The calculated vertical binding energies of the excess electron in anionic clusters ((H₂O) ₆ ^? 0.37÷0.66 eV and (NH₃) ₁₃ ^? 0.26 eV) agree well with the experimental values of 0.50 eV and 0.22 eV obtained from photoelectron spectra. A cavity model of solvated electrons in water and ammonium is considered.     

Photoelectron spectroscopy of radical anions

The photoelectron spectroscopy of a number of radical anions has been investigated. We find the following electron affinities: EA(C₃) =1.981 ±0.020 eV, EA(C₃H) = 1.858 ±0.023 eV, EA(C₃H₂) = 1.794 ± 0.025 eV, EA(C₃O) = 1.34±0.15 eV, EA(C₃O₂) = 0.85±0.15 eV, EA(C₄O)= 2.05±0.15 eV, and EA(CS₂) = 0.895± 0.020 eV. The structure and bonding for each of these ions is discussed.     

An efficient method for large scale configuration interaction calculations

An efficient method of handling large scale configuration interaction calculations is developed and applied to the H₂O molecule as a test case. The method, which is based upon matrix partitioning, is shown to be capable of calculating the ¹B₁ spectrum of H₂O to an accuracy level of 0.1 eV for each state with very moderate computational effort.     

Photoelectron spectroscopy of (CO2)n(H2O) m − clusters

Photoelectron spectra of (CO₂)_nH₂O^? (2≤n≤8) and (CO₂)_n(H₂O) ₂ ^? (1≤n≤2) were measured at the photon energy of 3.49 eV. The spectra show unresolved broad features, which are approximated by Gaussians. The vertical detachment energies (VDEs) were determined as a function of the cluster size. For (CO₂)_nH₂O^?, the VDE-n plots exhibit a sharp discontinuity between n=3 and 4; the VDE value is ≈3.5 eV at n=3, while it drops down abruptly to 2.59 eV at n=4. This discontinuity in VDE is ascribed to "core switching" at n=4; a C₂O ₄ ^? dimer anion forms the core of (CO₂)_nH₂O^? for n≤3, while a monomer CO ₂ ^? is the core for n≥4. The (CO₂)₂(H₂O) ₂ ^? ion has a VDE of 2.33 eV, indicating the presence of a CO ₂ ^? monomer core in the binary clusters containing two H₂O molecules.     

Interaction of dioxygen with the platinum Pt19/SnO2/H2 cluster: DFT calculation

The adsorption of the O₂ molecule onto the surface of the Pt₁₉ platinum cluster deposited onto the tin dioxide crystal surface in the presence of dissociated hydrogen molecule has been calculated by the density functional theory method within the generalized gradient approximation (GGA-PBE) with periodic boundary conditions and a projector-augmented plane-wave (PAW) basis set. It has been demonstrated that the oxygen molecule can be adsorbed without a barrier onto the free surface of the Pt₁₉/SnO₂/H₂ cluster to form a superoxy isomer with one Pt-O bond (the energy of elimination of the oxygen molecule is 0.75 eV), which converts almost without a barrier to more stable peroxide isomers with two Pt-O bonds (the energy of elimination of the O₂ molecule is 1.2?1.7 eV). The energy of elimination of the oxygen molecule from the isomers with two-coordinated oxygen positions at the cluster edges is 2.10?2.53 eV. The isomers with mono- and tricoordinated oxygen positions are less energetically favorable than the isomers with two-coordinated oxygen positions. The process of addition of the oxygen molecule to the platinum cluster and elimination of the water molecule formed in the reaction Pt₁₉/SnO₂/H₂ + O₂ → Pt₁₉/SnO₂/O + H₂O is energetically favorable by 1.6 eV.     

Theoretical studies of excited states of H3O and of core-excited NH3: Comparisons with equivalent core analysis of NH3 core-excitation spectra and implications for the radiation chemistry of aqueous systems

The H₃O radical has been studied within the ab initio LCAO SCF MO model. A flexible basis set including diffuse basis functions at both O and H has been used in order to represent the excited states adequately. Calculated excitation energies are 1.87, 2.87–3.16, and 3.36–3.47 eV; the calculated ionization energy is 4.75 eV. These represent well the experimental values (good to ±0.3 eV) of 1.6, 2.9, and 3.5 eV for excitation, and 5.0 eV for ionization, deduced by equivalent core analysis of high energy electron impact energy loss studies of NH₃. Similar explicit calculations on the N-1s core-excited states of NH₃ have also been made to examine directly the equivalent core concept. “Excited states” (relative to the lowest bound core-excited state) at 1.72, 2.85–3.09, and 3.32 eV, and the “ionization energy” of 4.68 eV, agree well with experiment and support the equivalent core concept. The possible significance of these H₃O results in the radiation chemistry of aqueous media is discussed in view of the fact that the maximum in the absorption spectrum of the hydrated electron lies near that of H₃O.     

Experimental and theoretical binding energy spectra and momentum distributions for the valence orbitals of H2O

The binding energy spectra (10–46 eV) and momentum distributions of the valence orbitals of H₂O have been measured using a new high-sensitivity binary (e,2e) electron spectrometer employing position-sensitive detectors. The binding energy spectrum shows a previously unreported feature at = 27 eV which is shown to be associated with the (2a₁)^?1 ionization process. The region between 25 and 46 eV is compared with previous (e,2e) and X-ray photoelectron measurements as well as with several existing and new many-body calculations indicating a splitting of the 2a₁ ionization pole strength. In addition the separate momentum distributions of the three outer valence orbitals of H₂O have been obtained from deconvoluted binding energy spectra run at a series of azimuthal angles. The results, which show considerably improved signal-to-noise ratio over earlier measurements using single-channel instrumentation are compared with spherically averaged momentum distributions calculated with a variety of wavefunctions.     

Activation energy of hydrogen migration by relay in the O2/Pt19/SnO2/H2 + n H2O system

In the framework of investigation of active and stable electrocatalysts for fuel cells, the hydrogen migration by relay with the consecutive formation of H₂O molecules in the O₂/Pt₁₉/SnO₂/H₂·nH₂O → O/Pt₁₉/SnO₂·nH₂O + H₂O system was simulated. The simulations were performed by the density functional theory (DFT) method with the generalized gradient adjustment (GGA=PBE) under periodic boundary conditions in the projector augmented plane wave (PAW) basis set with a pseudo-potential using the VASP program package. At the cathode on the platinum cluster surface, the oxygen molecules without a barrier form peroxide complexes that dissociate with an energy decrease. The protons transferred via the proton-conducting channels from the anode to cathode form first OH groups bound to the platinum cluster and then H₂O molecules that are easily separated from the cluster (～0.2 eV). The proton transfer process proceeds by relay and involves several water molecules.     

Processes of dissociative electron capture by 20-hydroxyecdysone molecules

The peculiarities of dissociative electron capture by 20-hydroxyecdysone molecules with the formation of fragment negative ions were studied. In the region of high electron energies (5–10 eV), processes of skeleton bond rupture are accompanied by the elimination of H₂O and H₂ molecules. In the region of thermal energies of electrons (≈0 eV), the mass spectrum is formed mainly by the [M−nH₂O]^.− (n=1–3) and [M−H₂−nH₂O]^.− (n=0−3) ions that are generated exclusively by the rearrangement. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 709–712, April, 2000.     

Crystal and band structure of a layered bismuth oxalate: (C3N2H12)[Bi(C2O4)2.5]·H2O

A 2-D oxalate-containing bismuth(III) compound of formula (C₃N₂H₁₂)[Bi(C₂O₄)_2.5]·H₂O has been hydrothermally synthesized and characterized by single crystal X-ray diffraction. The Bi atoms and oxalate units form a 2-D layered structure with a 12-membered aperture. The crystal band structure, calculated by the DFT method, shows that the title compound is an insulator with a band gap of 3.19?eV, a value consistent with the experimental value of 3.29?eV.     

ChemInform Abstract: Cross Sections and Product Kinetic Energy Analysis of H2O+-H2O Collisions at Suprathermal Energies.

The H₂O⁺-H₂O reaction is studied at center-of-mass collision energies in the range 0.5-25 eV.     

Why Are B ions stable species in peptide spectra?

Protonated amino acids and derivatives RCH(NH₂)C(+O)X · H⁺ (X = OH, NH₂, OCH₃) do not form stable acylium ions on loss of HX, but rather the acylium ion eliminates CO to form the immonium ion RCH = NH ₂ ⁺ . By contrast, protonated dipeptide derivatives H₂NCH(R)C(+O)NHCH(R′)C(+O)X · H⁺ [X = OH, OCH₃, NH₂, NHCH(R″)COOH] form stable B₂ ions by elimination of HX. These B₂ ions fragment on the metastable ion time scale by elimination of CO with substantial kinetic energy release (T _1/2 = 0.3–0.5 eV). Similarly, protonated N-acetyl amino acid derivatives CH₃C(+O)NHCH(R′)C(+O)X · H⁺ [X = OH, OCH₃, NH₂, NHCH(R″)COOH] form stable B ions by loss of HX. These B ions also fragment unimolecularly by loss of CO with T _1/2 values of ～ 0.5 eV. These large kinetic energy releases indicate that a stable configuration of the B ions fragments by way of activation to a reacting configuration that is higher in energy than the products, and some of the fragmentation exothermicity of the final step is partitioned into kinetic energy of the separating fragments. We conclude that the stable configuration is a protonated oxazolone, which is formed by interaction of the developing charge (as HX is lost) with the N-terminus carbonyl group and that the reacting configuration is the acyclic acylium ion. This conclusion is supported by the similar fragmentation behavior of protonated 2-phenyl-5-oxazolone and the B ion derived by loss of H-Gly-OH from protonated C₆H₅C(+O)-Gly-Gly-OH. In addition, ab initio calculations on the simplest B ion, nominally HC(+O)NHCH₂CO⁺, show that the lowest energy structure is the protonated oxazolone. The acyclic acylium isomer is 1.49 eV higher in energy than the protonated oxazolone and 0.88 eV higher in energy than the fragmentation products, HC(+O)N⁺H = CH₂ + CO, which is consistent with the kinetic energy releases measured.     

Thermal-energy charge transfer of Ar+ with H2O: Internal and kinetic energy of the product H2O+

The reaction of Ar⁺ with H₂O has been investigated at near-thermal energy. The product ions H₂O⁺ and ArH⁺ account for 90 and 10% of the total reaction rate, respectively. Kinetic energy measurements and emission spectroscopy of the H₂O⁺ product ions are reported. It is concluded that at least 60% of H₂O⁺ ions are in the X? state with ≈2.4 eV vibrational energy while up to 40% are in the à state with a mean vibrational energy of 1.4 eV; the à state vibrational distribution has been determined. It is shown that both H₂O⁺ states are populated via an energetically “non-resonant” charge transfer process.     

Quantum chemical DFT calculations of the local structure of the hydrated electron and dielectron

The adiabatic bound state of an excess electron is calculated for a water cluster (H₂O) ₈ ^? in the gas phase using the DFT-B3LYP method with the extended 6-311++G(3df,3pd) basis set. For the liquid phase the calculation is performed in the polarizable continuum model (PCM) with regard to the solvent effect (water, ? = 78.38) in the supermolecule-continuum approximation. The value calculated by DFT-B3LYP for the vertical binding energy (VBE) of an excess electron in the anionic cluster (VBE(H₂O) ₈ ^? = 0.59 eV) agrees well with the experimental value of 0.44 eV obtained from photoelectron spectra in the gas phase. The VBE value of the excess electron calculated by PCM-B3LYP for the (H₂O) ₈ ^? cluster in the liquid phase (VBE = 1.70 eV) corresponds well to the absorption band maximum λ_max = 715 nm (VBE = 1.73 eV) in the optical spectrum of the hydrated electron hydr e _hydr ^? . Estimating the adiabatic binding energy (ABE)e _hydr ^t- in the (H₂O) ₈ ^? cluster (ABE = 1.63 eV), we obtain good agreement with the experimental free energy of electron hydration ΔG ₂₉₈ ⁰ (e _hydr ^? ) = 1.61 eV. The local model (H₂O) ₈ ^2? of the hydrated dielectron is considered in the supermolecule-continuum approximation. It is shown that the hydrated electron and dielectron have the same characteristic local structure: -O-H{↑}H-O- and -O-H{↑↓}H-O-respectively.     

Model calculation of local versus hyperspherical mode selective dissociation of H2O

Hyperspherical H₂O^* resonances excited to energies ≲1 eV above the electronic ground state H₂O^* → H + OH dissociation threshold have lifetimes ≈ 45 ps, at least ten times longer than near-degenerate local H₂O^* resonances. The results are evaluated and analysed using fast-Fourier-transform (FFT) propagation of quantum wavefunctions representing H₂O stretching vibrations modeled by coupled Morse oscillators.     

Rydberg series in the absorption spectra of H2O and D2O in the vacuum ultraviolet

The photoabsorption cross section of molecular H₂O and D₂O has been determined in the range from hν = 10eV to 20 eV with 0.03 Å resolution. A refined analysis of the Rydberg series including the rotational line shapes of several bands to locate the band origins and a comparison with recent ab initio calculations is given. In the region of continuous absorption we have assigned a p-type and an s-type Rydberg series leading to the ²A₁ and the ²B₂ state respectively with quantum defects δ ≈ 0.75 and δ ≈ 1.36.     

Repulsive potentials for the interaction of oxygen atoms with the noble gases and atmospheric molecules

Repulsive potentials between about 0.2 eV and 20 eV are determined for interactions of oxygen atoms with the noble gas atoms and with H₂, N₂, O₂, NO, CO, CO₂ and H₂O molecules from incomplete total scattering cross sections. Good agreement with theory is obtained for the noble gases. The potentials for the interaction with molecules obtained by assuming spherically symmetric potentials are compared with the same potentials computed by averaging the cross sections for different orientations of the molecules. By introducing reduced variables, the problem of finding two isotropic potential parameters is simplified to a search for one, the other being determined by a least-squares constraint.     

Stereochemical applications of mass spectrometry. 3—Energy dependence of the fragmentation of stereoisomeric methylcyclohexanols

Breakdown graphs have been constructed from charge exchange data for the epimeric 2-methyl-, 3-methyl- and 4-methyl-cyclohexanols. Although the breakdown graphs for epimeric pairs are essentially identical above ～12 eV recombination energy, significant differences are observed for the epimeric 2-methyl- and 4-methyl-cyclohexanols at low internal energies. For the 2-methylcyclohexanols the ratio ([M? H₂O]^+·/[M]^+·)_cis/([M? H₂O]^+·/[M]^+·)_trans is 3.2 in the [C₆F₆]^+· charge exchange mass spectra. This is attributed to both energetic and conformational effects which favour the stereospecific cis-1,4-H₂O elimination for the cis epimer. The breakdown graph for trans-4-methylcyclohexanol shows a sharp peak in the abundance of the [M? H₂O]^+· ion at ～10 eV recombination energy which is absent from the breakdown graph for the cis epimer. This peak is attributed to the stereospecific cis-1,4-elimination of water from the molecular ion of the trans isomer; the reaction appears to have a low critical energy but a very unfavourable frequency factor, and alternative modes of water loss common to both epimers are observed at higher energies. As a result, in the [C₆F₆]^+· charge exchange mass spectra the ([M? H₂O]^+·/[M]^+·)_trans/([M? H₂O]^+·/[M]^+·)_cis ratio is ～24, compared to the value of 13 observed in the 70 eV EI mass spectra. No differences are observed in either the metastable ion abundances or the associated kinetic energy releases for epimeric molecules.