Reactions of HBr+ ions in the 2Π i , v + quantum states with H2 and HBr molecules

The mechanisms and kinetics of low-temperature ion-molecular reactions between the Br⁺, HBr⁺, and DBr⁺ions and the HBr, DBr, H₂, and D₂ molecules were studied. The HBr⁺ (i,v ⁺) and DBr⁺(i,v ⁺) ions were prepared in separate spin-orbit (i) and vibrational (v ⁺) states by resonance multiphoton ionization in a free flow of halogen halides (HBr and/or DBr) with hydrogen, deuterium, or inert gases (Ar, He). The effectiveness of various reaction channels, including the exchange of charges, H and D atoms, and H⁺andD⁺ ions, was studied. The quantitative data on the kinetics of these reactions were obtained for separate quantum states of the ions. The resonance ionization of one of the two ion isotopomers H⁷⁹Br⁺(D⁷⁹Br⁺) or H⁸¹Br⁺(D⁸¹Br⁺) was used to study and compare the effectiveness of various ion-molecular reaction channels.     

The effect of internal excitation on the collision induced dissociation of I+2(2Πg,υ) ions

Cross sections for collision induced dissociation of 0.65 to 3.2 keV I⁺₂(²Π_g, υ) ions in I⁺₂(²Π_g, υ) + N₂(X ¹Σ⁺_g, υ = 0) interactions have been determined. Reaction cross sections for I⁺₂(²Π_{$\text{3}\text{2}$,g}, υ) ions in low vibrational levels vary smoothly from 6 to 10 A² with increasing kinetic energy. Dissociation cross sections for I⁺₂(²Π_{$\text{1}\text{2}$,g}, υ) ions are larger than those involving ground state ions. Processes involving highly excited metastable states of I⁺₂ are not observed in this investigation.     

Thermal investigation of diamine complexes of Zn(II) in the solid state

The complexes [Zn(en)₃]X2·n H₂O, where en = ethylenediamine, X = Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄, n = 1 or 0.5, and [Zn(tn)₂]X₂·n H₂O, where tn=1,3-diaminopropane, X=Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄, n = 0 or 0.25, have been synthesized and their thermal investigations carried out. The complexes were characterized by elemental analysis and IR spectral data. These complexes have been observed to decompose through several isolable as well as non-isolable complex species as intermediates during heating. [Zn(tn)₂]SO₄ undergoes solid-state phase transition in the temperature range 126–145°C. ZnenSO₄ and ZntnX₂ (X = Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄) have been synthesized pyrolytically in the solid state from their corresponding mother diamine complexes. ZnenSO₄ and ZntnX₂ (X = Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄) complexes decompose through non-isolable hemidiamine species. ZnX₂ (X = Cl^? or Br^?) complexes of tn undergo melting after formation of the monodiamine species. In contrast, the corresponding en complexes undergo melting at non-stoichiometric composition. Diamine (en or tn) is found to be bridging in all monodiamine (en or tn) complexes; whilst their mother complexes possess chelated en or tn. The thermal stability sequence of en and tn complexes of Zn(II) is ZnCl₂ < ZnBr₂ < ZnSO₄. ΔH values are reported for some steps of decomposition. Possible mechanistic paths have been reported for each step of decomposition.     

Laser-induced fluorescence in supersonic nozzle beams predissociation in the Rb2 C1πu and D 1πu states

By exciting Rb₂ in a supersonic nozzle beam with a pulsed dye laser in the C ¹Π_u-X ¹Σ⁺_g and the D ¹Π_u-X ¹Σ⁺_g band system, we find evidence tor different predissociation processes The products appear as follows from the C state, Rb^* (5 ²P_{$\text{3}\text{2}$}) exclusively, and from the D state Rb*(4²D_{$\text{3}\text{2}$}) predominantly, followcd by Rb^*(5 ²P_i-5²S) cascade radiation In addition, a lower bound of D_e(Rb₂X¹Σ⁺_g)? 3939± 10 cm^?1 is obtained.     

High-resolution HeI and HeII photoelectron spectra of the Zn 3d and Cd 4d orbitals in the zinc and cadmium dihalides: Ligand field splittings and intensity variations

We have recorded the high-resolution HeI and HeII photoelectron spectra of the Zn 3d and Cd 4d levels in gas-phase MX₂ molecules (M = Zn, Cd; X = Cl, Br, I). The d level spectra split into five peaks due to the combined effect of spin-orbit splitting and ligand field splitting on the d⁹ hole state, and the spectra have been fitted to a crystal field hamiltonian involving the cubic (C₄⁰) and non-cubic (C₂⁰) parts of the field from the halide ligands. Additional peaks in some spectra are due to vibrational splitting and configuration interaction. The ¦C₂⁰¦ value increases substantially from the chloride to the iodide for both Zn and Cd. Calculations of both the crystal field (C_{2 CF}⁰) and valence (C_{2 val}⁰) parts of C₂⁰ show that the increase in observed C₂⁰ is due to the C_{2 val}⁰ term attributed to the increase in covalency from the chlorides to the iodides. Shifts in the peak position due to the 2Σ_{$\text{1}\text{2 g}$} and 1Π_{$\text{3}\text{2 g}$} states from those expected on the ligand field basis. are attributed to slight bonding effects. These effecs cause a large discrepancy between calculated and observed C₄⁰ values. The intensities of the five Zn 3d peaks change markedly from HeI- to HeII-excited spectra. The Xα SW method has been used to calculate the intensities of the σ, π and δ 3d orbitals as a function of photon energy. These calculations show dramatic changes in intensity due. for example. to shape resonances. There is usually qualitative agreement between calculated and observed intensities.     

Theoretical studies of fine structure in the ground state of O2

The spin-spin and spin-orbit contributions to the fine-structure constant of O₂ in its X³Σ^−g state are determined by ab initio methods. For the spin-spin interaction λ_ss, an extensive configuration interaction (Cl) calculation is carried out with a Slater basis set of double-zeta quality. The correlation terms which affect λ_ss most are identified, and it is found that although each of these terms can change λ_ss drastically, their net effect tends to be self-cancelling. The spin-orbit contribution λ_so is evaluated by assuming that the lowest members of the excited states ^2S+1Σ⁺_g and ^2S+1Π^±_g for S = 0, 1, 2 correctly describe the perturbation. Using ground-state SCF orbitals to construct single-configuration wavefunctions for these states, we find that the ¹Σ⁺_g state is the dominant contributor. Approximately 80% or 105% of the total splitting constant λ_ss + λ_so is recovered depending on whether theoretical or experimental energy denominators are used for λ_so, respectively.     

Theoretical spectroscopy and metastability of BeS and its cation

Multiconfiguration self-consistent field and multiconfiguration reference interaction including the Davidson’s correction techniques were employed to calculate the potential energy curves (PECs) of the BeS/BeS⁺ electronic states correlating to the 4/5 lowest dissociation limits. After nuclear motion treatment, we deduced reliable spectroscopic data for the neutral and cationic bound states. For BeS, the transition moments and spin-orbit couplings were also evaluated and used later with the PECs to deduce the rovibronic transition probabilities and the radiative lifetimes in the low-lying states, and to investigate the unimolecular decomposition processes of BeS (X¹Σ⁺, A¹Π, ³Σ⁺ and B¹Σ⁺) leading to Be(¹S_g) + S(³P_g). The prominent mechanism is a spin-orbit induced predissociation via the repulsive BeS(1³Σ⁻) state. Finally, we give the single ionization spectrum of BeS (X¹Σ⁺) populating the BeS⁺ (X²Π, 1²Σ⁻, 1²Σ⁺, 1²Δ, 2²Σ⁺, 2²Π and 3²Π) electronic states. The adiabatic ionisation energy of BeS is estimated to be ∼9.15 eV.     

Time and spectrally resolved fluorescence of Cl*2 and ArCl* in Cl2 doped Ar Under state selective pulsed photoexcitation with synchrotron radiation

Synchrotron Radiation is used to selectively excite chlorine and Cl₂ doped argon in the VUV region. Stationary fluorescence and excitation spectra of the 1¹Σ _u ⁺ , 2¹Σ _u ⁺ and 2³Πg Cl ₂ ^* states and of the ArCl*(B?X) transition are obtained. The excitation threshold of ArCl*(B) in Ar/Cl₂ system is found to be 1,285±5 Å and that of ArCl(C) at ～1,260 Å. The formation of ArCl* and Cl*₂(2³Πg) is discussed in terms of recent potential curves data. A detailed time resolved study is reported which allows us to determine precisely the radiative lifetime of ArCl*(B) state (5.2 ns) and numerous kinetic parameters of this system, to estimate theC state energy and to discuss the relaxation and mixing process of the ArCl*(B) and (C) states. A two ladder multilevel kinetic model is described which accounts for the experimental results and shows the difficulty of studying this particular ArCl* system as compared to the closely related XeCl* and KrCl* ones.     

High-resolution UV photoelectron spectrum of CO2

The highly-resolved HeI photoelectron spectrum of CO₂ is presented and its vibrational structure studied in detail. In the X? ²Π_g ionic state the v₃ antisymmetric mode is found to be excited in double quanta (v_1-v_2-v₃ = 0. 0. 2) with energy hv₃ = 181 meV. In the C? ²Σ_g⁺ state a single quantum of the same mode is found to be excited (hv₃ = 189 meV) in combination with a v₁ excitation. Vibronic interaction with vibrational levels in the B? ²Σ_u⁺ state of the ion is suggested to promote this (1, 0, 1) excitation. It is established that inelastic scattering processes contribute to the vibrational structure in the C? ²Σ_g⁺ band. The spin-orbit splitting in the X? ²Π_g is determined to be 19±1 meV and 10±2 eV in the ā²Π_u state. Vibronic structure is resolved in the X? ²Π_g band where the Renner-Teller coupling constant is determined to be ? = 0.21±0.02 and the vibrational energy of the v₂ mode as 60±7 meV. In the ā²Π_u state the v₂ energy is found to be hv₂ = 60 meV from the observed hot-band structure.     

CS+(B2Σ+ → A 2Πi) fluorescence from penning excitation of CS

The energy transfer reation of He(2³S) + CS was studied spectroscopically in a flowing afterglow apparatus. The CS⁺(B²Σ⁺ → A ²Π_i) transition is identified via three members of the Δν = 0 sequence (406–415 nm). The spin-orbit splitting of the (0, 0) band of CS⁺(A ²Π_i) is 301 ± 5 cm^?1. A weak emitting system (280–340 nm) is tentatively identified as CS⁺(B²Σ⁺→ X²Σ⁺).     

High resolution photoelectron studies: Electric field gradient splittings of Cd and Sn 4d energy levels in organometallic compounds

High resolution photoelectron spectra of Me₂Cd (Me = CH₃) in the gas phase, and organotin compounds in the solid state show that the 4d⁹ final state produced in the photoelectron experiment splits in the presence of ligand fields. Only the C₂⁰ crystal field term (the term that transforms like the electric field gradient) contributes to the splitting. The 4d_{$\text{3}\text{2}$} splitting in Me₂Cd and trans-Me₂Sn(BzBz)₂ (BzBz = anion of dibenzoylmethane) are 0.21 ± 0.01 eV and 0.35 ± 0.1 eV respectively. The observed 4d_{$\text{5}\text{2}$} linewidth for Ph₄Sn (Ph = C₆H₅) of 0.67 eV indicates that very narrow linewidths can be obtained on molecular nonconducting solids. The constant spin-orbit splitting values, combined with nuclear field gradients from Mössbauer and NQR measurements, strongly indicate that a previously proposed explanation for the increase in apparent spin-orbit coupling in Cd metal is untenable.     

Rotational analysis of the A—X bands of S+2

The S⁺₂ (A²Π_u-X²Π_g) emission system from sulphur monochloride in a helium flowing afterglow has been analysed in the 5000–6000 Å region. Molecular constants for the S⁺₂ (A²Π_u, X²Π_g) states have been determined and are compared with previous estimates. Equilibrium bond lengths of S⁺₂ are found to be: X²Π_g,r_e = 1.8226 ± 0.0010 Å and A²Π_u, r_e = 2.0441 ± 0.0013 Å.     

Geometric and electronic structure of ground and excited states of groupVA diatomics. A theoretical LCGTO-MP-LSD study

LCGTO-MP-LSD calculation was performed for the ground and several low-lying excited states of homo- (N₂, P₂, As₂, and Sb₂) and hetero-nuclear (PN, AsN, AsP, AsSb, SbN, and SbP) groupVA diatomics. For all the systems the ground state is found to be¹Σ⁺. For N₂ and P₂, the¹Σ _g ⁺ ground state is followed by the³Σ _u ⁺ ,³Π _g ,³Δ _u ,¹Π _g , and¹Δ _u low-lying exited states while for As₂ the order is found to be³Σ _u ⁺ ,³Δ _u ,³Π _g ,¹Δ _u ,¹Π _g . Finally for Sb₂ the relative stability of excited states is³Σ _u ⁺ ,³Δ _u ,¹Δ _u ,³Π _g ,¹Π _g . For the hetero-nuclear diatomics the¹Σ⁺ ground state is, in the case of PN, AsN, AsP, SbN, and SbP, followed by the³Σ⁺,³Δ,³Π,¹Π and¹Δ low-lying excited states while for the AsSb diatomic an inversion of stability of the two last singlets occurs. The calculated spectroscopic parameters (Re, ωe, andDe) are in good agreement with all the available experimental results while, theTe values are overestimated by about 0.5 eV. Mulliken population analysis shows that both homo- and hetero-nuclear groupVA diatomics are essentially triple bonded systems.     

Spin-orbit interaction in the excited states of the dihalogen ions F+2, Cl+2 and Br+2

The ²II_u state of Br⁺₂ shows an unusually large difference between the vibrational frequencies of its two spin-orbit components. It is shown that this can be understood from the combined effects of correlation and spin-orbit interaction, which is largely due to the partial localisation of the hole in the ion. The same mechanism can be held responsible for vibrational and rotational anomalies in the corresponding state of Cl⁺₂ and F⁺₂.     

HeIα photoionisation cross-section determination of Br atoms

An extended electron modulation spectroscopy method is described which allows the accurate determination of photoionisation cross sections of transient species relative to those of precursor compounds. In this paper cross section at 584 Å for atomic and molecular bromine transitions from neutral ground to lowest ionic states have been measured relative to that of the HBr⁺ (X²Π_1/2,3/2)←HBr(X¹Σ⁺) ionisation. Using the cross section of this HBr transition as an absolute standard and with relative cross-section data for ionisations leading to the accessible excited ionic states of Br⁺ and Br⁺₂, absolute total angle-integrated cross sections for the valence shell ionisation process in Br⁺ and Br⁺₂ are presented.     

Energy transfer processes in reactions of He(2 3S) and Ne(3P0,2) with CS2

A comparative spectroscopic study in the visible and ultraviolet ranges was conducted on the flowing afterglows resulting from the reactions of He(2 ³S) and Ne(³P_0,2) metastables with CS₂. Penning ionization was found to be the predominant energy transfer process. However, electron—ion recombination within the afterglows constitutes a major secondary process and gives rise to the most intense emitting system, CS(A ¹ Π → X ¹Σ⁺). Both afterglows were found to produce the CS⁺₂($\text{B}$²Σ⁺_u-$\text{X}$²Π_g), CS⁺₂($\text{A}$²Π_u-$\text{X}$²Π_g) and CS(a ³Π-X ¹Σ⁺) emission systems as well as some atomic sulfur emission lines. Some intensity differences were observed and are interpreted in terms of energetics and the formation mechanisms of the emitting species. A moderately strong CS⁺(A ²Π_i-X ²Σ⁺) emission system was also observed in the ehlium afterglow. In addition, a weak, sharp group of bands in the 390–420 nm range in the helium afterglow has been determined to be due to the presence of a small amount of He⁺ ions. This group of bands consists of two overlapping emission systems and are identified as CS(B ¹Σ⁺ → A ¹Π) and CS⁺(B ²Σ⁺ → A ²Π_i).     

An electrical conductivity (EC) study of the thermal dissociation of [Co(NH3)6]X3 and [Co(en)3]X3 complexes

The thermal dissociation of the [Co(NH₃)₆]X₃ (X = Cl^?, Br^?, I^?, and NO^?₃), [Co(en)₃]X₃ (X = Cl^?, Br^?, I^?, NO^?₃, HSO^?₄ and $\text{1}\text{2}$ C₂O^2?₄), cis- [Co(en)₂Cl₂]Cl, and trans-[Co(en)₂ClBr]NO₃ complexes was investigated by an electrical conductivity (EC) technique. During the thermal dissociation reactions, liquid or semi-liquid phases are formed which cause large increases in the EC of the compound. The effect of concentration of the complex in a matrix medium as well as the composition of the matrix material on the EC curves were also determined.     

Collisional deactivation of laser-excited Br*(2P12) atoms with halogen and interhalogen molecules

Deactivation rates of spin-orbit excited Br*(²P_{$\text{1}\text{2}$}) atoms by halogens I₂, Br₂, and Cl₂ and interhalogens IBr, ICl and BrCl have been measured by laser-excited, time-resolved infrared emission techniques. The results are effectively explained in terms of a collision complex formation model.     

Optical absorption spectra of praseodymium acetate complexes in solution

Results of analyses of the solution spectra of Pr³⁺ in the acetates of praseodymium, magnesium, calcium and cadmium complexes are presented. Slater-Condon (F₂, F₄ and F₆), configurational interaction (α,β), spin-orbit (ξ_4f), nephelauxetic ($\text{β}$) bonding (δ) and Judd-Ofelt (T₂T₄ and T₆) intensity parameters are evaluated. Judd-Ofel intensity relationship has been used in the calculation of electric dipole line-strengths. Theoretical evaluation of predicted radiative lifetimes (τ_R) of the electronic excited states ³P₁, ³P₀ and ¹D₂ of Pr³⁺ in four diff been carried out.