Electron affinities of the lanthanides

The electron affinities (EA's) of the lanthanides (La through Tm) have been determined from the expression EA = IP₁ ? C)r^?1)_n1, where IP₁ is the first ionization potential and (r^?1)_n1 is the relativistic radial integral of an electron in the unfilled shell, the constant C includes the quantum numbers n, 1 of the partly filled shells and the atomic number Z of each element. The EA's vary from +0.5 eV (La) to –0.2eV (Tm) which is consistent with other semi-empirical estimates for certain lanthanide elements.     

Photoelectron and vacuum ultraviolet spectra of a series of fluoroethers

Fluoroethers of the F(CF(CF₃)CF₂O)_nCHFCF₃ (n = 1-4) type have their lowest ionization potentials about 3.5 eV higher than ordinary ethers. Their ultraviolet absorption spectra also begin at high frequencies, at about 80000 cm^-1 or 10 eV. Both spectra are complex indicating the existence of several close lying molecular orbitals in these compounds.     

1,1-Dimethyl-1-silaethylene : Heat of formation,ionization potential and the energy of the siliconcarbon π-bond

The thermodynamic cycle consisting of thermal decomposition and dissociative ionization processes for 1,1-dimethyl-1-silacyclobutane is calculated. The heat of formation and the ionization potential (IP) for 1,1-dimethyl-1-sila-ethylene (DMSE) have been obtained: ΔH^o_f(DMSE) = 15.5 ± 5 kcal/mol; IP(DMSE) = 7.5 ± 0.3 eV. The siliconcarbon π-bond energy in DMSE is estimated: D_π(SiC)  28 ± 8 kcal/mol.     

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.     

Electron impact ionization of small silver and copper clusters

Using a quadrupole mass spectrometer, relative cross sections for electron impact ionization of neutral Ag _n and Cu _n clusters withn=1 ... 4 have been measured for electron energies between threshold and 125 eV. From the results, the following ionization energies were obtained: Ag₂: 7.26±0.1 eV, Ag₃: 6.19±0.2 eV, Ag₄: 6.33±0.3 eV, Cu₂: 7.46±0.15 eV, Cu₃: 6.14±1.0 eV, Cu₄: 7.00±0.6 eV. With only two exceptions, these values agree with other data published for Ag₂, Cu₂, Cu₃ and Cu₄.     

The gas phase X-ray photoelectron spectrum of N,N-dimethyl-p-nitroaniline

The N1s and O1s regions of gaseous N,N-dimethyl-p-nitroaniline have been studied by X-ray photoelectron spectroscopy. The N1s (-NO₂) peak is ≈0.5 eV broader than the N1s (-NH₂) peak, indicating the presence of intense, unresolved shake-up. A shake-up peak has been observed in the O1s region at 2.1 eV higher binding energy than the main peak, with a relative intensity of 50%. The results have been compared with the corresponding features in the paranitroaniline and in the solid, and it has been found that the O1s shake-up intensity remains essentially unchanged while the N1s shake-up is enhanced in going to the solid. Comparison has also been made with a CNDO/S CI calculation which somewhat underestimates the relative intensities but is in good overall agreement with experiment.     

CEPA calculations on open-shell molecules. VI. The first ionization potential of HCO

According to an investigation by Dyke et al. (1980) HCO seems to be one of the rare cases in which the correlation energy of the neutral molecule is smaller (in absolute value) than that of the first monopositive ion, such that the ΔSCF method yields a value for the first vertical ionization potential (IP _v ) which is larger than the experimental value. In order to understand this observation we have performed a series of SCF and CEPA calculations on HCO and HCO⁺ using as many as ten different orbital basis sets. The best ΔSCF result for IP _v is 9.24 eV, i.e. slightly smaller than the “experimental electronic” IP _v of 9.38 eV. Inclusion of electron correlation lowers IP _v as long as small basis sets are used, the convergence with increasing basis size is very slow. Extrapolation to a complete basis leads to a CEPA estimate of 9.26±0.10 eV for IP _v (and 8.05 ±0.10 eV for the adiabatic IP) which shows that the correlation contribution to IP _v is indeed very small. The reason for this is that the gain in correlation energy in HCO due to the presence of the unpaired electron is compensated by a loss of core correlation energy since the low-lying antibonding in-plane C-O-π- orbital is only partially available for excitation in HCO, but fully available in HCO⁺.     

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.     

Plenary lecture: Ion enthalpies and their application in mass spectrometry

The experimental determination of ionization and appearance energies is discussed, together with the calculation of heats of formation of ions. Results are presented for the ions [C_nH_2n+1]⁺, [C_nH_2n+2N]⁺ and [C_nH_2n+1O]⁺. The low temperature (～350K), low energy (12.1eV) mass spectra of some alkanes, amines and alcohols are presented and discussed.     

Feshbach-resonances and dissociative electron attachment of H2O

In order to obtain a better understanding of the dissociative electron resonance capture processes of H₂O we have remeasured the ionization efficie The relative intensities of these curves are strongly dependent on the ion focusing conditions; the observed maxima however (7.0 eV, 9.1 eV, 11.8 eV) a We interpret the resonances as due to Feshbach states associated with the three lowest Koopmans' ions of H₂O; this interpretation is supported by a     

Study of optoelectronic energy bands and molecular energy levels of tris (8-hydroxyquinolinate) gallium and aluminum organometallic materials from their spectroscopic and electrochemical analysis

For the purpose of investigating electro-molecular absorption bands, energy gaps, E_g and molecular energy levels (ionization potential, IP and electron affinity, EA) of tris (8-hydroxyquinolinate) gallium and aluminum, spectral analysis in conjunction with electrochemical measurements was carried out. UV-Vis-NIR and FTIR spectroscopic measurements were used to assign the electronic and molecular absorption bands in both of the materials. The XRD and scanning electronic microscopy (SEM) technique showed the amorphous nature. From the recorded data of cyclic voltammetry (CV) and materials absorption coefficient, HOMO, LUMO energy levels and energy gaps for Gaq3 and Alq3 were calculated. A bit smaller value of energy gap for Gaq3 (2.80 eV) compared to that of Alq3 (2.86 eV) has been ascribed to the differences in electronic configuration and coordinated bond lengths related to the central metal atom with respect to the quinolinate ligands. A higher value of HOMO energy level for the Alq3 (IP = 6.3 eV) revealed the need of higher potentials to oxidize its molecules comparing to that of Gaq3 (IP = 5.8 eV). It was observed that cationic metals have a direct effect on the physical and chemical behaviors of such organometallic materials that can be exploited to be used in tuning their properties to match the desired application in OSC and/or OLED technologies.     

Threshold photoionization behaviour of (Li2O)Lin clusters produced by a laser vaporization source

We report on the production of small and medium size lithium and lithium oxide clusters by a laser vaporization cluster source. The isotopomeric distribution of natural lithium allowed to identify Li_kO clusters as the most abundant components in the mass spectrum. Photoionization efficiency curves of Li_kO clusters with photon energies from 3.4 to 4.7 eV were measured for 8 ≤ k ≤ 27. Using linear extrapolation of the increase in photoionization efficiency with photon energy, ionization potentials were extracted. With the chemical bond of the O^2- anion to two Li atoms, leaving n = k-2 valence electrons in the (Li₂O)Li_n clusters, clear shell closure effects are present at n = 8 and n = 20.     

Translational energy distribution of excited deuterium atoms produced by controlled electron impact on D2

The Balmer-β line of the excited deuterium atom [D*(n = 4)] produced in e—D₂ collisions has been measured at high resolution (0.029–0.033 Å) and at various electron energies (17–100 eV). The translational energy distribution of D*(n = 4) has been calculated from analysis of its Doppler line shape. The distribution of D* has three major components as in the case of H*(n = 4) from H₂ reported in our previous paper. Their peaks lie at about 0, 6 and 8 eV. The excitation function of D* is found to have two thresholds at 17.4 and 26.4 eV. The second component of D* has a larger translational energy and a higher threshold than those of the corresponding component of H*. These results indicate that the contribution from the lowest doubly excited state, ¹Σ_g⁺(2pσ_u)², is much smaller for D₂ than that for H₂.     

Structure and energy of the positively ionized water clusters

Geometry optimization of small (H₂O)_n⁺ clusters (n ≤ 4) at the UHF/4–31 + + G^** level indicates that the cations consist of two fragments: the OH radical and the H_2n−1 O⁺_n−1 ion. The latter can be considered as a thermodynamically stable combination of a distorted H₃O⁺ ion and (n−2) H₂O molecules. The H bond between the fragments becomes weaker with increasing cluster size. Extrapolation of the adiabatic ionization potentials calculated for the (H₂O)_n oligomers (n ≤ 4) at the MP2 level to an infinite cluster size provides the value of approximately 8.7 eV, which can be presumably necessary for the ionization of liquid water in a vacuum. © 1997 John Wiley & Sons, Inc.     

Multiphoton ionization spectra of two caged amines

The multiphoton ionization spectra of quinuclidine (ABCO) and triethylenediamine (DABCO) have been measured. All of the observed resonances are two-proton transitions to low-lying localized Rydberg states. For ABCO the lowest energy transitions are assigned as ¹A₁ (3s) ← ¹A₁ (n) 4.84 eV, and ¹E (3p_xy) ← ¹A₁ (n), 5.42 eV. In the case of DABCO, orbitals localized on the nitrogens interact and are split into two new orbitals. In terms of the split orbitals the low energy resonances in DABCO are assigned as ¹E′[3p_xy(?)] ← ¹A₁ (n+_, 4.44 eV, and ¹E″ [3p_xy(+)] ← ¹A₁ (n+), 4.94 eV.     

Electron impact and single photon ionization cross sections of neutral silver clusters

Neutral silver atoms and small clusters Ag _n (n=1...4) were generated by sputtering, i.e. by bombarding a polycrystalline silver surface with Ar⁺ ions of 5 keV. The sputtered particles were ionized by a crossed electron beam and subsequently detected by a quadrupole mass spectrometer. In alternative to the electron impact ionization, the same neutral species were also ionized by single photon absorption from a pulsed VUV laser (photon energy 7.9 eV), and the photoionization cross sections were evaluated from the laser intensity dependence of the measured signals. By in situ combining both ionization mechanisms, absolute values of the ratio σ _e (Ag _n )/σ _e (Ag) between the electron impact ionization cross sections of silver clusters and atoms could be determined for a fixed electron energy of 46 eV. These values can then be used to calibrate previously measured relative ionization functions. By calibrating the results using literature data measured for silver atoms, we present absolute cross sections for electron impact ionization of neutral Ag₂, Ag₃ and Ag₄ as a function of the electron energy between threshold and 125 eV.     

Calculated ionization energies for a series of sesquiterpenes: comparisons with experimental vertical ionization energies and comments on related structure–activity relationships (SARs)

The energies of the highest-occupied molecular orbitals (HOMOs) are known to be excellent predictors of the reactivities of biogenic hydrocarbons, such as terpenes, with reactive atmospheric oxidants including O₃, OH, and NO₃. Structure–Activity Relationships (SARs) have also been effectively employed in such studies and related to HOMO energies and lowest ionization energies (ionization potentials). This study employs density function theory (DFT), at the B3LYP/6-31G** level, to predict vertical ionization energies (IP_v) for a structurally diverse group of sesquiterpenes, each of which has been reported in air samples collected in the lower troposphere. The availability of published UV photoelectron spectra for nine sesquiterpenes permits comparison of experimental and theoretical vertical ionization energy data. The experimental and theoretical data show a good correlation (average discrepancy ± 0.07 eV). This enables predictions of reactivities for sesquiterpenes whose tropospheric lifetimes may last only a few hours before their transformations into secondary organic aerosols (SOA) close to their emission sources.     

Self-assembly syntheses and crystal structures of triorganotin(IV) pyridinecarboxylate: 1D polymers and a 42-membered macrocycle

A series of new triorganotin(IV) pyridinecarboxylates with 6-hydroxynicotinic acid (6-OH-3-nicH), 5-hydroxynicotinic acid (5-OH-3-nicH) and 2-hydroxyisonicotinic acid (2-OH-4-isonicH) of the types: [R₃Sn (6-OH-3-nic)·L]_n (I) (R = Ph, L = Ph·EtOH, 1; R = Bn, L = H₂O·EtOH, 2; R = Me, L = 0, 3; R = n-Bu, L = 0, 4), [R₃Sn (5-OH-3-nic)]_n (II) (R = Ph, 5; R = Bn, 6; R = Me, 7; R = n-Bu, 8), [R₃Sn (2-OH-4-isonic·L)]_n (III) (R = Bn, 9, L = MeOH; R = Me, L = 0, 10; R = Ph, 11, L = 0.5EtOH) have been synthesized. All the complexes were characterized by elemental analysis, TGA, IR and NMR (¹H, ¹³C, ¹¹⁹Sn) spectroscopy analyses. Among them, except for complexes 5 and 6, all complexes were also characterized by X-ray crystallography diffraction analysis. Crystal structures show that complexes 1-10 adopt 1D infinite chain structures which are generated by the bidentate O, O or N, O and the five-coordinated tin centers. Significant O-H?O, and N-H?O intermolecular hydrogen bonds stabilize these structures. Complex 11 is a 42-membered macrocycle containing six tin atoms, and forms a 2D network by intermolecular N-H?O hydrogen.     

Atomistic modelling of the hydration of CaSO4

Atomistic modelling techniques, using empirical potentials, have been used to simulate a range of structures formed by the hydration of γ-CaSO₄ and described as CaSO₄·nH₂O (0<n<1). The hemihydrate phase (n=0.5) is of commercial importance and has been subjected to much experimental study. These simulation studies demonstrate significant water-matrix interactions that influence the crystallography of the hydrated phase. The existence of two types of hydration site has been predicted, including one within the Ca²⁺coordination sphere. Close correlation between water molecule bonding energy, Ca²⁺-O_w bond length and unit-cell volume have been established. This shows that as the number of water molecules within the unit cell increases, the bonding energy increases and the unit cell contracts. However around n=0.5, this process reaches a turning point with the incorporation of further waters resulting in reduced binding energy and an expanding unit cell.     

Flame-ion chemistry of the lanthanide metals Ce,Pr and Nd

A pair of premixed, H₂O₂Ar flames of fuel-rich (FR) and fuel-lean (FL) composition, both at atmospheric pressure and 2425 K, were doped with about 10⁻⁶ mol fraction of the lanthanide metals La, Ce, Pr and Nd; from a previous study, La was used as a benchmark. The metals produce solid particles in the flames and gaseous metallic species. The latter include metallic atoms A near the flame reaction zone, but only the monoxide AO, the oxide hydroxide OAOH and, in some cases, the dioxide AO₂ further downstream at equilibrium. Metallic ions (< 1% of the total metal) were observed by sampling the flames through a nozzle into a mass spectrometer. All of the observed ions can be represented by four hydrate series: (a) major signals of AO⁺·nH₂O (n = 0–3) for La, Ce, Pr and Nd; (b) small signals of AO₂H⁺·nH₂O (n = 0–2) for Ce, Pr and Nd; (c) still smaller signals of AO₂⁺·nH₂O (n = 0, 1) for Ce, Pr and Nd in the FL flame only; and (d) tiny signals of AOH⁺·nH₂O (n = 0, 1) for Pr and Nd in the FR flame only. The actual structures of some of these ions may not correspond to simple hydrates: e.g. AO⁺·H₂O = A(OH)₂⁺ = protonated OAOH; AO₂H⁺·H₂O = A(OH)₃⁺, etc. Since hydrogen flames contain essentially no natural ionization, a major objective was to consider probable ionization mechanisms for the metals. The primary reactions include both chemi-ionization, and thermal (collisional) ionization of AO whose ionization energy is low (about 5 eV). Some of the ions are formed by secondary ion/molecule reactions including three-body hydration, proton transfer, electron (charge) transfer, H atom abstraction by radicals and oxidation. In addition, the chemical ionization of the metallic species by H₃O⁺ was investigated. The flame-ion chemistry of these metals is discussed in detail.