An ab initio potential energy surface for the reaction N+ + H2 → NH+ + H

Preliminary results of ab initio unrestricted Hartree-Fock calculations for the potential energy surface for the reaction N⁺ + H₂ → NH⁺ + H are reported. For the collinear approach of N⁺ to H₂, the ³Σ^? surface has no activation barrier and has a shallow well (ca. 1 eV). For perpendicular approach (C_2v symmetry) the ³B₂ state is of high energy, the ³A₂ state has a shallow well but as the bond angle increases the ³B₁ state decreases in energy to become the state of lowest energy. Neither the collinear nor the perpendicular approaches give adiabatic pathways to the deep potential well of ³B₁ (HNH)⁺.     

Internal-energy-selected measurements on the relative cross section of the ion-molecule reaction NH3+(NH3, NH2)NH4+

A photoelectron-photoion coincidence technique is used to measure the internal-energy dependence of the ion-molecule reaction NH₃⁺(E_int+NH₃ → NH₄⁺ + NH₂ at thermal collision energy. The range in which the internal energy is varied, is enlarged by including in the experiment the electronically excited state of the NH₃⁺ ion. Special attention is paid to the possible influence of the product's kinetic energy on the measurements. The experimental results are analysed using a modified statistical model and compared with previous data.     

Chemical composition and crystal structure of β-alumina type R+-gallate (R+ = K+, NH+4)

The crystal structures of β-alumina type K⁺-gallate (K⁺-β-gallate), Mg²⁺-doped K⁺-β-gallate, and NH⁺₄-β-gallate were refined by the single crystal X-ray diffraction method. The positive charges of excess K⁺ ions in K⁺-β-gallate were compensated by O^2? ions in the mO site which coordinated with interstitial Ga³⁺ ions. The charge compensation mechanism mentioned above was changed by doping with Mg²⁺ ions. The excess charges in Mg²⁺-doped K⁺-β-gallate were compensated by the replacement of Mg²⁺ ions for Ga³⁺ ions at the middle of spinel block. No defects were found in NH⁺₄-β-gallate for the charge compensation, which was completely consistent with the result of thermal analysis that indicated a stoichiometric composition of NH⁺₄-β-gallate.     

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.     

On the reaction of Kr+ with hydrogen

The reaction of Kr⁺(²P_3/2) and Kr⁺(²P_1/2) with H₂ are examined using a conventional ICR and a tandem Dempster- ICR instrument. The accidentally near-resonant charge-transfer reaction of CO⁺ with Kr was used to prepare a nearly pure ²P_3/2 state Kr⁺ beam to evaluate rates of reaction of the ²P_3/2 and ²P_1/2 state with H₂. It was found that the Kr⁺(²P_3/2) reacts faster than the Kr(²P_1/2) and a negligible activation energy exists for both reactions.     

Delayed predissociation and collision-induced processes of the ammonia di-cation NH32+

Reactions of NH₃²⁺ di-cations, observed a few microseconds after formation by electron ionisation of ammonia, have been studied in a double-focusing mass spectrometer using techniques of ion translational energy spectroscopy. Fragmentation reactions occuring under unimolecular conditions correspond to predissociation processes, but lack of knowledge about states of NH₃²⁺ precludes any definitive interpretation. A partial tentative interpretation, using arguments by analogy with isoelectronic neutral species, is proposed. Almost all collision-induced fragmentations required electron transfer forming NH₃⁺ as an intermediate step, so the non-dissociative electron transfer processes were also studied. The most unexpected collision-induced fragmentation reaction was that which formed H₃⁺ fragment ions.     

1,2-Eliminations from (CH3)2NH+CH2CH3 and (CH3)2NH 2+ : Guided dissociations

1,2-Eliminations are a varied and extensive set of dissociations of ions in the gas phase. To understand better such dissociations, elimination of CH₂=CH₂ and CH₃CH₃ from (CH₃)₂NH⁺CH₂CH₃ (1) and of CH₄ from (CH₃)₂NH₂⁺ are characterized by quantum chemical calculations. Stretching of the CN bond to ethyl is followed by shift of an H from methyl to the bridging position in ethyl and then to N to reach (CH₃)₂NH₂⁺ + CH₂=CH₂ from 1. CH₃CH₃ elimination by H-transfer to C₂H₅⁺ to form CH₃NH⁺=CH₂ + CH₃CH₃ also takes place. (CH₃)₂NH₂⁺ eliminates methane by CN bond extension followed by β-H-transfer to give CH₂=NH⁺ + CH₄. Low-energy reactions resembling complex-mediated 1,2-eliminations occur and constitute a hitherto largely unrecognized type of reaction. As in many complex-mediated reactions, these reactions transfer H between incipient fragments. They are distinguished from complex-mediated processes by the fragments not being able to rotate freely relative to each other near the transition state for reaction, as they do in complexes. Most 1,2-eliminations are ion-neutral complex-mediated, occur by the just described lower energy reactions, have 1,1-like transition states, or utilize highly asynchronous 1,2 transition states. All of these avoid synchronized 1,2-transition states that would violate conservation of orbital symmetry.     

Chemiluminescent ion-molecule reactions in the system C+ + H2

The optical emission resulting from collisions between C⁺ ions and H₂ gas was measured in the energy range 2 to 20 eV_c.m.. The observed spectrum consists mainly of the CH⁺ A ¹Π → X ¹Σ⁺ band system; CH⁺ (A ^fΠ) is shown to be formed in the chemiluminescent reactio: C⁺(²P⁰) + H₂ → CH⁺(A ¹Π) + H(²S). The energy dependence of the emission cross section was measured. The occurrence of this reaction is discussed in terms of a electronic state correlation diagram for the system.     

The properties of clusters in the gas phase: ammonia about Bi+, Rb+, and K+

Thermodynamic data are reported for NH₃ clustered about Bi⁺, Rb⁺, and K⁺ in the gas phase. Unusually strong bondings of NH₃ to Bi⁺ suggests the probable importance of partial covalent bonding in stabilizing the first ligand cluster. Differences in relative bond strengths for NH₃ and H₂O about Rb⁺ andK⁺ are consistent with the results of extended Hückel calculations reported herein.     

Sensitization of the CN(B2Σ+ → X2Σ+) emission by Hg(63P0) metastables

The vibrational analysis of the CN(B²Σ⁺ → X²Σ⁺) emission sensitized by Hg(6³P₀) metastables has shown that the energy transfer process, Hg(6³P₀) + CN(X²Σ⁺) → Hg(6¹S₀) + CN(B²Σ⁺), populates the CN(B²Σ⁺) state in a non-Franck-Condon fashion. The relative vibrational populations for the ν = 0 to 4 states are 1.00, 0.56 ± 0.06, 0.26 ± 0.03, 0.11 ± 0.03 and 0.04 ± 0.01, respectively. Long-range attractive interaction between the Hg(6³P₀) atom and the CN(X²Σ⁺) radical is evidenced by the observed high rotational excitation of the CN(B²Σ⁺) radical following the energy transfer process.     

Collisional Dissociation of CH3O2+

The collision-induced breakup of CH₃O₂⁺ ions, produced in various binary ion—neutral reactions, was investigated in a drift experiment in the energy range from 0.2 to 1.2 eV. The products observed were HCO⁺ (50%) and H₃O⁺ (50%), independent of the collision energy inducing the breakup. The energy barrier for the breakup is 22 ± 6 kcal/mole.     

Coincidence studies of fluorescence and dissociation processes in electronic excited states of I2+, Br2+, IBr+ and ICl+

The PIFCO technique in which mass-selected photoion—fluorescence photon coincidences are counted, was used to investigate whether I₂⁺, IBr⁺ and ICl⁺ fluoresce. Measurements were made of lifetimes and fluorescence quantum yields of electronic excited states of these ions. Emission was discovered for I₂⁺ and IBr⁺, but ICl⁺ apparently does not fluoresce. Information on the radiative properties of Br₂⁺ was obtained as a by-product of the work on IBr⁺. Fragment ion kinetic energy releases were determined and provide information on dissociative ionization processes in the halogen and interhalogen ions studied.     

Ã2Σ+ → X̃+Π Emission spectra of the phosphaethyne cations,HCP+ and DCP+

The electron impact excited òΣ⁺ → X?⁺Π emission spectra of HCP⁺ and DCP⁺ have been observed. The spin-orbit split 0-0 band has maxima at 593.7 and 599.0 nm for HCP⁺ and 593.6 and 598.8 nm for DCP⁺. Short progressions in the V₃(CP) vibration are observed. a₀, v₃ and the upper-state lifetime are determined.     

Imaging the Dissociation Dynamics of Si2+ via Two-Photon Excitation at 193 nm

In the one-color experiment at 193 nm, we studied the photodissociation of Si₂⁺ ions prepared by two-photon ionization using the time-sliced ion velocity map imaging method. The Si⁺ imaging study shows that Si₂⁺ dissociation results in two distinct channels: Si(³P_g)+Si⁺(²P_u) and Si(¹D₂)+Si⁺(²P_u). The main channel Si(³P_g)+Si⁺(²P_u)) is produced by the dissociation of the Si₂⁺ ions in more than one energetically available excited electronic state, which are from the ionization of Si₂(v=0-5). Particularly, the dissociation from the vibrationally excited Si₂(v=1) shows the strongest signal. In contrast, the minor Si(¹D₂)+Si⁺(²P_u) channel is due to an avoided crossing between the two 2²Π_g states in the same symmetry. It has also been observed the one-photon dissociation of Si₂⁺(X⁴Σ_g^-) into Si(1D2)+Si+(2Pu) products with a large kinetic energy release.     

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.     

Mobilities of H+3 and HeH+ ions in helium gas and rate coefficient for HeH+ + H2 → H+3 + He

The mobilities of mass-identified H⁺₃ and HeH⁺ ions in helium and the reaction rate coefficient for HeH⁺ + H₂ → H⁺₃ + He have been measured by a drift-tube quadrupole mass spectrometer at 300 K. The zero-field reduced mobilities of H⁺₃ and HeH⁺ ions, corrected to 273 K, are 31.0 ± 0.8 and 23.4 ± 0.6 cm² V^?1 s^?1 respectively. The reaction rate coefficient was found to be (1.26 + 0.16) × 10^?9 cm³s^?1 and was observed to be independent of the mean ion kinetic energy in the range from 0.04 to 0.3 eV.     

Stability constants of the Li+, Na+, H3O+, NH4+, Ag+, and K+ complexes of the cone conformer of tetraethyl p-tert-butyltetrathiacalix[4]arene tetraacetate in nitrobenzene saturated with water

Abstract  

From extraction experiments in the two-phase water–nitrobenzene system and γ-activity measurements, the stability constants of the tetraethyl p-tert-butyltetrathiacalix[4]arene tetraacetate (cone)·M⁺ complexes (M⁺ = Li⁺, H₃O⁺, NH₄ ⁺, Ag⁺, or K⁺) were determined in water-saturated nitrobenzene. It was found that these constants increase in the cation order NH₄ ⁺ < K⁺ < H₃O⁺ < Ag⁺ < Li⁺ < Na⁺.     

Imaging the [1+1] Two-Photon Dissociation Dynamics of Br2+ in a Cold Ion Beam

The [1+1] two-photon dissociation dynamics of mass-selected ⁷⁹Br₂⁺ has been studied in acold ion beam using a cryogenic cylindrical ion trap velocity map imaging spectrometer. The quartet 1⁴Σ^-_u,3/2 state of ⁷⁹Br₂⁺ is employed as an intermediate state to initiate resonance enhanced two-photon excitation to high-lying dissociative states in the 4.0-5.0 eV energy region above the ground rovibronic state. Total kinetic energy release (TKER) and the twodimensional recoiling velocity distributions of fragmented ⁷⁹Br⁺ ions are measured using the technique of DC-slice velocity map imaging. Branching ratios for individual state-resolved product channels are determined from the TKER spectra. The measured photofragment angular distributions indicate that the dissociation of ⁷⁹Br₂⁺ occurs in dissociative Ω=3/2 state via ΔΩ=0 parallel transition from the 1⁴Σ^-_u,3/2 intermediate state. Due to the considerable spin-orbit coupling effects in the excited states of ⁷⁹Br₂⁺, higher-lying dissociative quartet states are likely responsible for the observed photodissociation processes.     

Solvent extraction of H3O+, NH4+, Ag+, K+, Rb+ and Tl+ into nitrobenzene by using cesium dicarbollylcobaltate in the presence of a hexaarylbenzene-based receptor

From extraction experiments and γ-activity measurements, the extraction constants corresponding to the general equilibrium M⁺(aq) + 1·Cs⁺(nb) \rightleftarrows \rightleftarrows 1·M⁺(nb) + Cs⁺(aq) taking part in the two-phase water–nitrobenzene system (1 = hexaarylbenzene-based receptor; M⁺ = H₃O⁺, NH₄ ⁺, Ag⁺, K⁺, Rb⁺, Tl⁺; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Furthermore, the stability constants of the ML⁺ complex species in nitrobenzene saturated with water were calculated; they were found to increase in the series of Rb⁺ < K⁺ < Ag⁺, Tl⁺ < H₃O⁺, NH₄ ⁺.     

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.