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.     

Laser-induced photodissociation of He+2

The momentum distributions of He⁺ fragments from photodissociation of He⁺₂ ions have been recorded in a crossed-beams experiment. The discrete values of the kinetic energy releases can be predicted from the vibrational spacings in the ground state of the primary ions.     

Excited states of gaseous ions. V. The predissociation of the h2o+ ion

The B?² state of H₂O⁺ is predissociated twice. First, by the ã⁴B₁ state, giving OH⁺ + H fragments via spinorbit coupling interaction. Secondly, by a²A state, giving H ⁺ OH fragments via spin-orbit coupling and Coriolis interactions. A vibrational analysis of the photoelectron band of the B? state of H₂O⁺ and D₂O⁺ is carried out. This provides the vibrational frequencies of the H₂O⁺, D₂O⁺ and HDO⁺ ions, as well as a vibrational assignment of the peaks. The H₂O⁺ ion in its B?²B₂ state is found to have a OH bond length of 1.12 A and a valence angie of 78°.In order to describe the unimolecular fragmentation process, a distinction is introduced between the totally symmetric, optically active vibrational modes, and the antisymmetric ones which are coupled to the continuum. The former are supplied with photon or electron impact energy, but only the latter are chemically efficient. The dynamics of the dissociation process depends therefore on the couplings among normal modes. This is studied in the framework of two models. In Model 1, it is assumed that, as a result of the anharmonicity of the potential energy surface, only even overtones of the antisymmetric vibration are excited by Fermi resonance. In Model II, excitation of the odd overtones is provided by vibronic coupling. Model II is in better agreement with experiment than Model I. Calculated and experimental results have been compared on the following points: isotopic shift on the appearance potential of OH⁺ and OD⁺ ions, shapes of the photoionization curves, fragmentation pattern with 21 eV photons, presence of a unimolecular metastable transition, production of O⁺ ions. All the vibrational levels situated above the dissociation asymptote are totally predissociated. Autoionization is shown in this case to contribute only to the formation of molecular H₂O⁺ ions, and not to that of the OH⁺ fragments. For 21 eV electrons, the contribution due to direct ionization is calculated to represent about 25% of the total cross section, the rest being due to autoionization.     

Order—disorder in compounds LiMe2+VO4

The crystallographic order between the Li⁺ and Me²⁺ ions in some compounds LiMeVO₄ (Me = Mg, Co, Ni, Cu, Zn) has been investigated by vibrational spectroscopy. The Li⁺ and Me²⁺ ions are disordered in the cobalt and nickel compounds and ordered in the copper and magnesium compounds.     

Zero kinetic energy ions in dissociative attachment on triatomic molecules: S−/OCS,O−/CO2

The zero kinetic energy yield of S^? ions in OCS and O^? ions in CO₂, produced by dissociative electron attachment through the lowest shape resonance, has been measured in a quadrupole mass spectrometer with electrostatic filter for translational energy analysis. The relative cross sections for S^? and O^? ion formation associated with CO fragments excited up to the vibrational level υ = 4 are obtained.     

A method for the measurement of radiative lifetimes in ions: The A 2Πu level of F2+

A method for the measurement of radiative lifetimes in ions is described, in which a uniform electric field extracts radiating ions from a viewing field. Decay curves are obtained by measuring the decrease of light intensity as a function of field strength. The method is tested and applied by studying emission from the F₂⁺(A ²Π_u) vibrational levels ν = 6–9, yielding lifetimes of 1.3 ± 0.1 μs for ν = 6 and 1.5 ± 0.1 μs for ν = 7–9.     

Rate constant measurement for the reaction of D3+ with H2

The rate constant and the product distribution for the reaction of D₃⁺ with H₂ has been measured as a function of the D₃⁺ vibrational energy. In these experiments a mass analyzed beam of D₃⁺ ions is decelerated to less than 0.1 eV and is subsequently injected into an ion cyclotron resonance (ICR) cell where reaction with H₂ may occur. Ion detection is achieved using a conventional oscillator-detector. The number of D₃⁺-D₂ coliisions was varied from 0 to 10 by changing the D₂ pressure in the source of the first stage of the instrument.     

Experimental and theoretical study of the IR spectrum of [(CH2OH)3CNH3]2SiF6 crystal

[(CH₂OH)₃CNH₃]₂SiF₆, (tris(hydroxymethyl)aminomethane)₂SiF₆ crystal, abbreviated as (TRIS)₂SiF₆ crystal, exhibits a solid-solid phase transition (PT) at 182 K. The phase transition is connected with reorientational motion of SiF₆²⁻ and -CH₂OH groups. The vibrational infrared spectra of powdered (TRIS)₂SiF₆ crystal in Nujol and Fluorolube mulls were studied in the wide range of temperatures, from 320 K to 133 K. A wide region of internal vibrations of the TRIS⁺ and SiF₆²⁻ ions was investigated. Temperature changes of wavenumber, width, centre of gravity, and intensity of bands were analyzed to clarify the molecular mechanism of the phase transitions. Theoretical calculations were made based on density functional theory (DFT). The calculated normal vibrational modes of the molecules, their frequencies and intensities were compared with those obtained from experimental data.     

Random energy flow in the dissociation of energy selected bromobenzene and bromobenzene-d5 ions

The absolute rates of bromine atom loss in bromobenzene and deutorobromobenzene ions were measured as a function of the internal energy. The ions were prepared at selected energies by photoion photoelectron coincidence. The results were compared to the rates predicted by the statistical theory. The excellent agreement between theory and experiment indicates that the CH or CD vibrational modes participate fully in the energy flow of the isolated molecular ions, even though the CH and CD bonds are not involved in the formation of product C₆D⁺₅ fragment ions.     

à 2A1 → X̃ 2B1 emission spectrum of cis-1,2-difluoroethylene cation and the non-radiation decay of the à states of the haloethylene cations in the gaseous phase

The results of the search for the à → X? radiative relaxation of haloethylene cations in the gaseous phase are reported. Only in the case of cis-1,2-difloroethylene cation was an emission spectrum detected. It is identified as the à ²A₁ → X? ²B ₁ band system on the basis of photoelectron spectroscopic measurements. An assignment of the emission bands yields the vibrational frequencies of four of the A₁ fundamentals (under C₂, symmetry) for the X? state and one for the à state. Well resolved Ne(I) photoelectron spectra of cis- and trans-1,2-difluoroethylene are presented, from which some vibrational frequencies for these cations in the X? and à states are also obtained. The lifetimes of cis-1,2-difluoroethylene cation in the lowest vibrational levels of the à ²A₁ state have been measured. The decay of this cation is unusual as these levels are depleted both by, radiative, and pathways leading to fragment ions (C₂HF⁺). The lack of detectable emissions with other fluoro-, chloro- and bromo-ethylene cations is discussed and the likely symmetries of the à states are proposed.     

Spectroscopy of molecular ions: Laser-induced fragmentation spectra of N2O+, A 2Σ+-X2Π

The N₂O⁺ molecular ion is studied by laser-induced fragmentation in a mass-selected beam of ions employing a frequency-doubled pulsed dye laser operating at a resolution up to λ/Δλ=400000. Spectra in the wavelength range between 317.5 and 328.5 nm are presented which give new information about highly excited vibrational levels of the A ²Σ⁺ state. The rotational structure of the A ²Σ⁺(2,0,0)-X²Π(0,0,0) transition was observed with high resolution and analyzed by means of calculations. Molecular constants are determined with good accuracy.     

Unimolecular dissociations of excited C3H6O+: A comparative photoelectron—photoion coincidence study of 1,2-epoxypropane and acetone

The unimolecular fragmentation of internal energy selected 1,2-epoxypropane cations has been studied by fixed-wavelength photoelectron—photoion coincidence spectroscopy. Branching ratios for the prominent fragment ions are reported up to an ionization energy of I = 14 eV. It is shown that 1,2-epoxypropane cations initially formed with none or only little vibrational excitation in the electronic ground state do not dissociate, though their excess energy with respect to the lowest energetic fragmentation pathway is 1.25 eV. As the internal energy is increased, slow fragmentation into several dissociation channels is observed. This is used to explain a comparably slow dissociation process observed in the case of acetone molecular ions initially excited to their electronic à state. CH₂C(OH)CH₃⁺ and/or CH₃CHCHOH⁺ are proposed as precursors for these low-rate unimolecular reactions.     

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.     

Inversion Vibrational Energy Levels of PH3+(X2A2") Calculated by a New Two-dimension Variational Method

A new 2-D variational method is proposed to calculate the vibrational energy levels of the symmetric P-H stretching vibration (v1) and the symmetric umbrella vibration (inversion vibration) (v2) of PH₃⁺(X²A₂") that has the tunneling effect. Because the symmetric internal Cartesian coordinates were employed in the calculations, the kinetic energy operator is very simple and the inversion vibrational mode is well characterized. In comparison with the often used 1-D model to calculate the inversion vibrational energy levels, this 2-D method does not require an assumption of reduced mass, and the interactions between the v1 and v2 vibrational modes are taken into consideration. The calculated vibrational energy levels of PH₃⁺ are the first reported 2-D calculation, and the average deviation to the experimental data is less than 3 cm^-1 for the first seven inversion vibrational energy levels. This method has also been applied to calculate the vibrational energy levels of NH₃. The application to NH₃ is less successful, which shows some limitations of the method compared with a full dimension computation.     

The Raman spectrum of tetragonal Eu3+CaF2

The Raman spectrum of a tetragonal single crystal of the compound Eu_xCa_1-(3/2)x F₂(where x = 0.002) is reported. The main features of the spectrum are the ⁷F₀ - ⁷F₁ and ⁷F₀ → ⁷F₂ electronic transitions of Eu³⁺ ions located at a site of C₂ symmetry and vibrational transitions which involve movements of the europium ion. The characteristic phonon band of cubic CaF₂ is for the rare-earth doped crystal moved to a higher frequency and the corresponding Raman tensor is that for a crystal of tetragonal symmetry.     

H+ and OH− ions in aqueous solutions vibrational spectra of hydrates

The ions (H₂O ... H ... OH₂)⁺ and (HO ... H ... OH)^? are the simplest stable H⁺ and OH^? hydrates in aqueous acid and base solutions, respectively. Using the attenuated total reflection method, the IR spectra of aqueous HCl and KOH solutions are obtained and the assignment of the H₅O₂⁺ and H₃O₂^? vibrational frequencies is performed. The absorption spectrum of the OHO fragment is separated from the spectra of the solutions investigated. This spectrum exhibits a broad continuous band and two rather narrow bands at its background which are assigned to the antisymmetrical stretching vibration and to the bending vibrations of the fragment. A theoretical model is suggested which explains the origin of the continuum by a strong proton-phonon coupling. The model takes into account the large number of low-frequency vibrational modes of the system; the frequency dispersion for these modes is assumed to be sufficiently large. The continuous absorption bandshape is calculated in the Condon approximation. The theoretical absorption curve is in good agreement with experiment at reasonable values of the parameters involved.     

Thermal energy charge transfer reactions of Ar+ ions with HBr and DBr molecules

HBr⁺ (A²Σ⁺-X²Π_i) and DBr⁺ (A²Σ⁺-X²Π_i) emissions are found up to v′=1 and v^′=2, respectively, from the thermal energy charge transfer reactions of Ar⁺ with HBr and DBr molecules in a flowing afterglow apparatus. Both A-state vibrational distributions have a peak at the lowest vibrational level, which are inconsistent with those expected from the energy resonance and/or Franck-Condon factors for ionization. This discrepancy is explained in terms of the distortion of target molecules by approach of reactant ions. Both A-state rotational distributions show that energies partitioned into rotation decrease with increasing vibrational levels, whereas the internal energy is nearly constant for all vibrational levels. The vibrational and rotational distributions obtained suggest that the reaction occurs at a relatively short distance and the product has a broad translational energy distribution.     

The vibrational relaxation of I2 by H2 in a supersonic jet

The vibrational relaxation of I₂ by H₂ has been studied in a supersonic free jet. It was observed that the addition of 5% H₂ to the helium carrier gas greatly reduces the concentration of X ¹Σ⁺_g(ν″ = 1) I₂ in the jet as compared to the concentration in a pure helium carrier. From this observation we have determined that the average vibrational relaxation cross sections of H₂ is 7.1 times as large as that of helium. Since the average vibrational relaxation cross section of deuterium is at least as large as that of hydrogen, the mechanism responsible for this phenomenon appears not to be dominated by mass effects.     

Dynamics of the reaction H2+(He,H)HeH+. Influence of various forms of reactant energy on the total and differential cross section

Results of quasiclassical trajectory calculations of reactive processes between He atoms and H₂⁺ (υ, J) molecular ions in the collision energy interval 0.5–5.0 eV (c.m.) for a large number of selected υ, J combinations are analyzed with respect to the influence of the initial translational, vibrational, and rotational energy on the total and differential reaction cross sections. Vibrational energy is more effective in promoting the reaction than translational energy. Small rotational excitation has a negligible effect, whereas high rotational excitation has a similar influence on the reaction cross sections as the vibrational excitation of the same magnitude.     

Vibrational structure in the photoelectron spectrum of O2+2Σg− (σg2s)

Discrete vibrational structure has been observed in the photoelectron spectrum of oxygen at an ionization potential of 40.33 eV. Two levels, attributed to the O₂⁺²Σ_g^?(σ_g2s) final state, have been detected with a vibrational spacing of 0.071 eV.