Thermal energy collisions between metastable Ne⋆(2p 53s,3 P 0, 2) and H2(X,1Σ g + )

A crossed beam experiment is used to investigate the Ne*(2p ⁵ 3s,³ P _{0, 2}) ? H₂(¹Σ _g ⁺ ) collision at thermal energy (67 meV). The H₂ beam is supersonic, the Ne* beam is thermal. Different collision processes have been analyzed separately by means of a double chopping technique combined with a time of flight measurement. Ions produced by Penning effect and chemi-ionization have been separated from scattered metastable atoms by an accelerating electric field small enough to preserve a reasonable angular resolution: δ?(ions)=±5.5°, δ?(Ne*)=±1°, which allows a determination of differential cross sections. The attenuation method, combined with an absolute measurement of the total H₂ flux, has been used to measure the total cross section: σ _t =940±220a ₀ ² . Differential cross sections have been obtained, in arbitrary but unique unit, for the following processes: (1) elastic collisions, for a mixture (1:3) of para- and ortho-hydrogen; (2) rotationally inelastic collisions:J=0→2; (3) Penning ionization resulting into H ₂ ⁺ ions; (4) chemiionization yielding NeH⁺ ions.     

The interaction of metastable Ne(3s 3 P 2,3 P 0) atoms with alkali atoms

Using crossed beams of alkali atoms (Li, Na, K) and state-selected metastable Ne(3s ³ P ₂,³ P ₀) atoms, we have measured the energy spectra of electrons resulting in the respective Penning ionization processes at thermal collision energies. The spectra are very different for Ne(³ P ₂) and Ne(³ P ₀): those for Ne(³ P ₂) are broad due to a strongly attractive interaction potential with a well depth of 798 (30) meV (Li), 672(20) meV (Na), and 561(20) meV (K), those for Ne(³ P ₀) are narrow and compatible with van der Waals type attraction (well depth <50 meV). The Ne(³ P ₂) cross section exceeds the one for Ne(³ P ₀) by about an order of magnitude.     

The structure of the metallated iridium complex [(C8H12)Ir{P(OC6H3Me)(OC6H4Me)2} {P(OCH2)3CMe}]

The crystal structure of [(C₈H₁₂)$\text{Ir{P(OC}$₆H₃Me)(OC₆H₄Me)₂} {P(OCH₂)₃CMe}] has been determined. a 18.32, b 18.98, c 9.35 Å, U 3251 ų, Pn2_1^a, Z = 4, R = 0.048, 2541 observed data.The coordination about the iridium atom is distorted trigonal bipyramidal; the two phosphorus atoms are equatorial, the σ-bonded carbon is axial, and the bidentate cyclooctadiene is bonded axialequatorial. The IrC(axial) bonds are longer than the IrC(equatorial) bonds: 2.22, 2.26; 2.17, 2.19 Å. The IrC(σ) bond length is 2.19 Å, not significantly different from the formally π-bonded C to Ir distances. The IrP lengths of 2.201 and 2.240 Å and the PIrP angle of 108.7° are normal. The longer IrP bond is in the five-membered chelate ring. The inertness to substitution is discussed.     

Cadmium (5 1 P 1 → 5 3 P J) excitation transfer and 5 3 P J intramultiplet relaxation by collisions with molecular gases

Collisional 5 ¹ P ₁ → 5 ³ P _J spin changing fine structure transfer as well as 5 ³ P _J intramultiplet mixing induced by various molecular gases (H₂, D₂, N₂, CO, CO₂, CH₄, C₂H₆, C₃H₈, C₂H₄) have been investigated using a combined method of fluorescence and absorption spectroscopy. After pulsed optical excitation of the Cd(5 ¹ P ₁) level the time dependence of the population densities has been measured both for the Cd(5 ¹ P ₁) level as well as the three collisionally populated Cd(5 ³ P _J) levels. By analyzing the signal curves at different molecular gas pressures not only the ratios of 5 ¹ P ₁ → 5 ³ P _J population transfer cross sections but also the Cd(5 ¹ P _J), Cd(5 ³ P _J) quenching cross sections and the Cd(5 ³ P _J) intramultiplet population transfer cross sections have been obtained.     

Quenching rate constants for Ne3P2) metastable atoms at room temperature

Rate constants for quenching of Ne³P₂) metastable atoms have been measured at room temperature by the flowing afterglow technique for 12 reagents; Ar, Kr, Xe, H₂, N₂, CO, HCl, F₂, Cl₂, NF₃, N₂F₄ and N₂O. The values range from ≈5 × 10^?11 cm³ molecule^?1 s^?1 for H₂ and CO up to ≈42 × 10^⊥-11 cm³ molecule^?1s^?1 for Cl₂ and F₂. Comparison with similar data for He(2³S) and Ar(³P₂) suggests that the thermal quenching cross sections follow the trends δ(Ar, ³P₂) > δ(Ne, ³P₂) ? δ(He, 2 ³S). The major exceptions seem to be N₂, CO and Kr which have usually small quenching cross sections for Ar(³P₂).     

Structural chemistry of bimetallic hydride complexes of titanium and aluminium: I. Crystal and molecular structure of [(η5-C5H5)2,Ti(μ-H)2AlH2]2(CH3)2NCH2CH2N(CH3)2C6H6

The structure of a titanium aluminium hydride complex of composition [(C₅H₅)₂TiAlH₄]₂(CH₃)₂NC₂H₄N(CH₃)₂C₆H₆ has been determined by X-ray diffraction. The complex forms triclinic crystals with unit cell dimensions a = 8.406(2), b = 10.117(2), c = 11.269(3) Å; α = 112.01(2)°, β = 109.25(2)°, γ = 87.04(2)°, space group P$\text{1}$, Z = 2 and density d = 1.21 g/cm³. The structure was refined to give a discrepancy index R = 0.056. The crystals are composed of centrosymmetric molecules of (Cp₂TiAlH₄)₂TMEDA (Cp = η⁵-cyclopentadienyl) and molecules of crystal benzene. Two moieties of Cp₂TiH₂AlH₂ are linked by a tetramethylethylenediamine molecule (r_AlN 2.11 Å). The aluminium atom is bonded to a titanium atom by a double hydride bridge (r_AlH b = 1.8, 1.6 Å, r_TiH b = 1.6 Å), and has trigonal bipyramidal stereochemistry, [H₄N] (r_AlH t = 1.6 Å).     

Molecular structure and conformational composition of gaseous 1,1-dichloro-2-bromomethyl-cyclopropane and 1,1-dichloro-2-cyanomethyl-cyclopropane as determined by electron diffraction

The molecular structure of the title compounds have been investigated by gas-phase electron diffraction. Both molecules exist as about equal amounts of the two gauche conformers. There is no evidence for the presence of a syn conformer, but small amounts of this form cannot be excluded. Some of the important distance (r_a) and angle (∠_α) parameters for 1,1-dichloro-2-bromomethyl-cyclopropane are: r(CH) = 1.095(19) Å, r(C₁C₂) = 1.476(11) Å, r(C₂C₃) = 1.517(31) Å, r(CCH₂Br) = 1.543(32) Å, r(CCl) = 1.752(6) Å, r(CBr) = 1.950(13) Å, ∠CCBr = 110.5(1.9)°, ∠ClCCl = 111.9(6)°, ∠CCC = 117.5(1.3)°, σ₁ (CC torsion angle between CBr and the three-membered ring for gauche-1) = 116.2(5.6)°, σ₂ = −132.7(7.6). For 1,1-dichloro-2-cyanomethyl-cyclopropane the parameter values are: r(CH) = 1.101(16) Å, r(C₁C₂) = 1.498(9) Å, r(C₂C₃) = 1.544(21) Å, r(C₂C₄) = 1.497(33) Å, r(CCN) = 1.466(26) Å, r(CN) = 1.165(8) Å, r(CCl) = 1.754(5) Å, ∠CCCN = 113.7(2.0)°, ∠CCC = 122.8(1.6)°, ClCCl = 112.5(4)°, σ₁ = 113(13)°, σ₂ = −124(10)°.     

Accurate comparison of Hel,NeI photoionization and He(23, 1 S), Ne(3s 3 P s,3 P 0) penning ionization of argon atoms and dimers

Using crossed beams and mass spectrometric ion detection, we have investigated the ionization of argon atoms and dimers in a skimmed supersonic beam by HeI (58.4 nm) and NeI (73.6, 74.4 nm) photons and by He(2^3,1 S) and state selected Ne(3s ³ P ₂,³ P ₀) metastable atoms. The cross section ratioq ₂₂/q ₁ (i.e. the cross sectionq ₂₂ for formation of Ar ₂ ⁺ ions from Ar₂ divided by the total ionization cross sectionq ₁ for Ar atoms), arbitrarily normalized to 1 for HeI impact, is found to vary weakly as follows: HeI/NeI/He(2^{3, 1} S)/Ne(³ P ₀)Ne(³ P ₂)=1/1.136(9)/0.893(4)/1.034(12)/0.985(9). The results are qualitatively interpreted using available information on the intermolecular potentials and the two different ionization processes. The observation thatq ₂₂/q ₁ is 5% larger for Ne(³ P ₀) than for Ne(³ P ₂) is attributed to anomalies in the respective branching ratios for formation of the Ar+(² P _3/2)/Ar⁺(² P _1/2) ion states in conjunction with differences in the stability of the formed Ar-Ar⁺(² P _3/2) and Ar-Ar⁺(² P _1/2) molecular ions.     

Partial differential cross sections for inelastic He++Ne collisions at low energy

We report differential cross section measurements with high angular resolution for different channels of the inelastic processes He⁺+Ne→He⁺+Ne* and He⁺+Ne→He*+Ne⁺, for collision energies between 100 and 200 eV. For the Ne states (2p ⁵3s)^1,3 P ₁, which decay optically, we determined the fraction with the alignment at right angles to the scattering plane. The results are used to discuss the mechanism of the processes and the influence of the spin-orbit interaction upon the collision.     

Classical models for electronic degrees of freedom: Quenching of Br*(2P1/2) by collision with H2 in three dimensions

Three-dimensional classical trajectory calculations have been carried out for the quenching of Br*(²P_1/2) by collision with ground-state H₂, using an approach that describes the electronic as well as heavy-particle (i.e. transition, rotation, vibration) degrees of freedom by classical mechanics. We find a sizeable quenching cross section (≈$\text{1}\text{2}$ Ų), with essentially all of the collision products having H₂ vibrationally excited to υ = 1, i.e. near-resonant EV transfer dominates the non-resonant ET,R processes. This is in agreement with experimental results.     

Collisional depolarization of excited114Cd 5s5p 3 P 1 atoms by collisions with molecular gases

Depolarization of excited¹¹⁴Cd 5s5p ³ P ₁ atoms induced by collisions with various molecular gases (N₂, H₂, D₂, CO, CO₂, CH₄, C₂H₆, C₂H₄) has been investigated using polarized fluorescence spectroscopy. After pulsed optical excitation of the Cd 5³ P ₁ level with appropriately polarized light the temporal behaviour of Zeeman quantum beats has been observed showing the influence of collisional destruction of orientation and alignment. By analyzing the signal curves at different molecular gas pressures the corresponding depolarization cross sections for¹¹⁴Cd atoms in the 5³ P ₁ state have been obtained. With regard to a test of a nuclear spin decoupling model for the collisions the cross sections were compared with previously measured hyperfine structure transfer cross sections of¹¹³Cd 5s5p ³ P ₁ atoms.     

The total ionisation cross section and the large angle differential cross section for the system He(21S, 23S) + Ar,N2

We have measured the total ionisation cross section Q_ion(g) and the large angle differential cross section σ(θ, g) for the system He(2¹S, 2³S)+ Ar, N₂ at energies 0.05 < E_c.m. (eV) < 6. This energy range is covered by applying two different discharge sources for the production of metastable atoms. In the atomic beam the He(2³S) level is most abundant with relative populations C = 0.91±0.01 and C = 0.96±0.01 for thermal energy range and the superthermal energy range, respectively. A quench lamp is used for the quenching of the (2¹S) level population. In the thermal energy range, σ(θ, g) and Q_ion(g) are in fair agreement with experimental results of other authors and with calculated cross sections based on the optical potential given by Siska. In the superthermal energy range, the He(2³S)+Ar optical potential is modified to describe our experimental data. The slope of the repulsive branch of the real potential is increased for r < 2.85 Å; in the imaginary potential a saturation to a constant (or even decreasing) value for internuclear distances less than 2.5 Å is introduced.     

Population transfer between the fine-structure levels 5s5p 3 P 1 and 5s5p 3 P 0 of114Cd atoms by collisions with molecular gases

Fine-structure mixing of excited¹¹⁴Cd 5³ P _J atoms induced by collisions with various molecular gases (N₂, H₂, D₂, CO, CH₄, C₂H₆) has been investigated by a combined method of absorption and fluorescence spectroscopy. After pulsed optical excitation of the Cd(5³ P ₁) level, the time dependence of the population densities has been measured simultaneously both for the 5³ P ₁ state and for the collisionally populated 5³ P ₀ state. By analyzing the signal curves at different molecular gas pressures cross sections for collisional transfer between the¹¹⁴Cd 5³ P ₁ and 5³ P ₀ levels as well as the quenching cross sections for the 5³ P levels have been obtained.     

Collision cross sections for excitation energy transfer in Na* (3P 1/2)+K(4S 1/2)⇔Na*(3P 3/2)+K(4S 1/2) processes

The cross sections for the excitation energy transfer between the 3² P _J states of sodium atoms by collisions with ground-state potassium atoms have been measured by resonant Doppler-free two-photon spectroscopy, where the population densities of directly pumped and collisionally excited Na(3P _J )(J=1/2, 3/2) levels were probed by counter-propagating Na(3P _J ) → Na(4D _{3/2, 5/2}) excitation and detected with the thermionic diode. Cross sections of σ(3P _1/2 → 3P _3/2)=190 Ų±20% and σ(3P _3/2 → 3P _1/2)=100 Ų±20% were found. The theoretical calculations taking into account the long-range interaction termsR ^?6,R ^?8 andR ^?10 yield a value σ(3P _1/2 → 3P _3/2)=165 Ų. On the basis of these long-range interaction potentials the differential cross section has been calculated and compared with recently published experimental data. Very good agreement between the theoretical and experimental data was found.     

The crystal and molecular structure of dicarbonylbis(diphenylethylphosphine) platinum(0) Pt(CO)2[P(C6H5)2(C2H5)]2

The complex dicarbonylbis(diphenylethylphosphine)platinum, Pt(CO)₂[P(C₆H₅)₂(C₂H₅)]₂, crystallizes in either of the enantiomorphous space groups P3₁21 (No. 152) and P3₂21 (No. 154) with cell dimensions a = 10.64(1), c = 22.06(1) Å, U = 2163 ų; p_c = 1.564 g/cm³ for Z = 3, p_m = 1.55(3) g/cm³. The intensities of 1177 independent reflections have been determined by counter methods with MoKα monochromatized radiation. The structure has been solved by the heavy atom method. The refinement, carried out by full-matrix least squares down to a final R factor of 0.042, has enabled the absolute configuration of the crystal sample (space group P3₁21) to be ascertained. The molecule is roughly tetrahedral, and has the metal atom lying on a two-fold axis of the cell. Bond parameters are: PtC = 1.92(2) Å, PtP = 2.360(4) Å, CPtC = 117(1)° and PPtP = 97.9(2)°. The PtC₂ and PtP₂ moieties make a dihedral angle of 86.0(3)°. The overall C₂ symmetry of the molecule is probably only a statistically averaged situation, a disorder in the PtCO interactions being apparent from the orientations of the thermal ellipsoids of the C and O atoms.     

On the sudden approximation of cross: computational tests and factorization of cross sections and related scattering phenomena

A sudden approximation recently derived by Cross using a semiclassical treatment of the orbital motion is recast into a form which permits factorization of differential and integral degeneracy averaged cross sections, opacities as a function of final angular momentum quantum number, the scattering amplitude, and the phenomenological cross section which describes spectral line broadening. Calculations are done using an average of initial and final orbital angular momentum quantum numbers for the partial wave parameter for ArN₂, ArTIF, H⁺H₂ and Li⁺H₂. The results indicate that the method is a good approximation for integral cross sections and opacities when the energy sudden approximation is valid and when the coupling of the orbital motion is important.     

The structure of the H3O+ (hydronium) ion

Near Hartree-Fock level ab initio molecular orbital calculations on H₃O⁺ and a minimum energy structure with θ(HOH) = 112.5° and r(OH) = 0.963 Å and an inversion barrier of 1.9 kcal/mole. By comparing these results to calculations on NH₃ and H₂O, where precise experimental geometries are known, we estimate the “true” geometry of isolated H₃O⁺ to have a structure with θ(HOH) = 110-112°, r(OH) = 0.97–0.98 Å and an inversion barrier of 2–3 kcal/mole. Our prediction for the proton affinity of water is ≈ 170 kcal/mole, which is somewhat smaller than the currently accepted value.     

Experimental determination of repulsive potentials between alkali ions (Li+, Na+, and K+) and N2 and CO molecules

Integral scattering cross sections have been measured for alkali ions (Li⁺, Na⁺ and K⁺) in the energy range 500–4000 eV scattered by room temperature N₂ and CO molecules through effective laboratory angles greater than 5 × 10^?3 rad. The repulsive potentials deduced from the cross sections are represented bya practically identical formula for the Na⁺N₂ and Na⁺CO systems, and for the K⁺CO systems, respectively, while the repulsive potentials of the Li⁺N₂ system are somewhat smaller than those of the Li⁺CO system at larger intermolecular distances.