The structure and energy of SiH+5. comparisons with CH+5 and BH5

Differences between SiH⁺₅ and CH⁺₅ are more significant than the similarities. The proton affinity of SiH₄ exceeds than of CH₄ by ≈25 kcal/mol. but the heat of hydrogenation of SiH⁺₃ is smaller than that of CH⁺₃ by nearly the same amount. Like CH⁺₅ the C₅ structures of SiH⁺₅ are preferred, but SiH⁺₅ is best regarded as a weaker SiH⁺₃—H₂ complex. D_3h, C_2v, and C_4v forms are much higher in energy and SiH⁺₅ should not undergo hydrogen scrambling (pseudorotation) readily, as does CH⁺₅ The neutral BH₅ is only weakly bound toward loss H₂, and the D_3h. C_2v, and C_4v forms are also high in energy. The contral-atom electronegativities, C⁺ > B > Si⁺, control this behavior. The electronegativities also determine the ability to bear positive charges. Thermodynamically. SiH⁺₅ and SiH⁺₃ are more stable than CH⁺₅ and CH⁺₃, respectively; hydride transfer occurs from SiH₄ to CH⁺₃ and proton transfer from CH⁺₅ to SiH₄.     

Laser induced photodissociation of H+2 and D+2 ions

Photodissociation of H⁺₂ and D⁺₂ has been observed in a crossed beam experiment. A laser used as photon source. The ion and laser beam cross each other inside the laser cavity. The momentum spectra of the resulting H⁺ or D⁺ fragments are recorded with a mass spectrometer. From the spectra the excess kinetic energy is calculated. These values agree with the theoretically expected ones within the experimental error. From the measured intensity distribution the relative population for several vibrational states in the primary ion beam is calculated. Our values deviate from the usual assumed Franck-Condon pattern as well as from the values reported by Dunn. The angular dependence of the fragments is also measured. This dependence indicates a polarization of the primary beam perpendicular to its direction.     

Solution raman spectra and normal coordinate analysis of the H3CPH+3 and H3CPD+3 cations

The Raman spectra of solutions of H₃ CPH₃⁺ and H₃ CPD₃⁺ in aqueous concentrated hydrochloric and deuterochloric acid are reported together with polarisation data. A complete vibrational assignment is given on the basis of C_3v, symmetry except for the inactive A₂ mode. A set of valence force constants and potential energy distributions have been calculated from the data of the two isotopes H₃ CPH₃ and H₃⁺ CPD⁺₃. For H₃ CPD⁺₃ the potential energy distribution demonstrates strong interaction between the P-C stretching and the symmetrical PD₃ deformation mode.     

AB initio calculations of the stability of the OH+4 and FH+3 ions

Some geometric configurations of the OH⁺₄ and FH⁺₃ ions have been calculated by the SCF MO LCAO method using linear combinations of gaussian lobe functions. The total electronic energies of the systems under study are lower than the sum of the energies for H₂O and H⁺₂ or OH⁺₃ and H, and HF and H⁺₂ or FH⁺₂ and H, respectively.     

Ci calculations of the low lying electronic states of the radical SiH3, SiH+3 and SiH−3

SCF and CI calculations for the silicon-hydrogen compounds SiH₃, SiH⁺₃ and SiH^? with D_3h and C_3v geometries are carried out f     

Rotation energies for deuterated H+3 oscillators in zero-point states of vibration

Previous ab initio studies of deuterated H⁺₃ molecular ions are extended to include rotational modes for the zero-point states of vibration. Rotation energies are obtained using direct numerical diagonalization of vibration—rotation hamiltonian matrices, and nuclear wavefunctions as superpositions of mode-coupled anharmonic rotationless vibrators and related prolate symmetric top eigenfunctions. Relevance to recent searches for interstellar H₂D⁺ is noted.     

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.     

A further study of the near-thermoneutral reactions O2H+ + H2 ⇌ H3+ + O2

The forward and reverse rate coefficients for the reactions (1) O₂H⁺ + H2 ? H₃⁺ + O₂ and (2) O₂D⁺ + D₂ ? D₃⁺ + O₂ have been determined in a SIFT at 80 and 300 K, from which values of the enthalpy and entropy changes in the reactions have been obtained. The data indicate that the proton affinity of H₂ is greater than that of O₂ by 0.33 ± 0.04 kcal mole^?1; similary, the deuteron affinity of D₂ is 0.35 ± 0.04 kcal mole^?1 greater than that of O₂. The measurements of entropy changes confirm that O₂H⁺ has a triplet electronic ground state.     

Photodissociation of the dimer ions Ar+2, Ne+2, and (CO2)+2

The tandem quadrupole photodissociation mass spectrometer has been used to study photodissociation reactions of Ar⁺₂, Ne⁺₂, and (CO₂)⁺₂. The cross sections for photodissociation of Ar⁺₂ exhibited a strong dependence on ion source pressure, varying from 2 × 10 ^?18cm² at 0.1 torr to 6 × 10^?19cm² at 0.5 torr. A large photodissociation cross section (2 × 10^?17cm² for the reaction (CO₂)⁺₂ → CO⁺₂+ CO₂ was observed at the red end of the visible spectrum (580–620 nm) suggesting that this may be an important reaction in CO₂ rich planetary ionspheres such as that of Mars.     

Endothermic reactions of Ni+ with H2, HD and D2

An ion-beam apparatus is employed to study the reaction of Ni⁺ with H₂, HD, and D₂ as a function of kinetic energy. These reactions lead to the endothermic formation of NiH⁺, NiH⁺ and NiD⁺, and NiD⁺, respectively. Interpretation of the threshold for these processes yields the average bond energies, D⁰(Ni⁺H) = 1.86 ± 0.09 eV and D⁰(Ni⁺D) = 1.90 ± 0.14 eV. The total reaction cross sections for all three systems are similar; however, a striking isotope effect is observed for Ni⁺ reacting with HD. The dependence of the cross sections on relative kinetic energy is discussed in terms of simple models for reaction.     

Vibrational characteristics and structures of allyl groups C3H+5, C3H·5 and C3−5 involved in σ, π and ionic bondings with metals

Several spectroscopic characteristics of the structure and of the nature of internal bonds in allyl groups C₃H⁺₅, C₃H^·₅ and C₃H^?₅ are compared and clearly deduced from infrared and Raman spectra of some organometallic compounds.     

Kinetics of the association of H+3 with H2 at low temperatures

The rate constant for the formation of H⁺₅ (D⁺₅) at (86 ± 3) °K by the three-body process has been determined (k₃(H) = (2.16 ± 0.10) × 10^?28 × 10^?28 cm⁶/molecule² sec and k₃(D) = (1.47 ± 0.20) × 10^?28 cm⁶/molecule² sec) in a high pressure mass spectrometer. Comparison of this result with published rate data at 300 °K indicates the reaction has an apparent activation energy of ?1.5 kcal/mole.     

A kinetic study of proton transfer reactions of NH+4, CH3NH+3, and PH+4 with calcium atoms

Cross section measurements for the proton transfer reactions of NH⁺₄, CH₃NH⁺₃, and PH⁺₄ with Ca(g) have been obtained over a range of low ion kinetic energies. For all reactions studied the cross sections drop sharply with increase in ion kinetic energy, indicating exothermic behavior. The results show that Ca(g) is an unusually strong base with a proton affinity in excess of 9.2 eV. Cross sections for the PH⁺₄Ca reaction are an order to magnitude higher than those for the NH⁺₄Ca reaction for ion energies between one and three eV. This effect is not explained by simple theories of ion-induced dipole interactions. It is suggested that the enhanced rate of the PH⁺₄Ca reaction may be due to d-orbital participation.     

Jahn—Teller effects in substituted benzene cations. III. Gas phase emission spectrum of sym-C6Cl3H+3

The gas phase emission spectrum of 1, 3, 5-C₆Cl₃H⁺₃ was obtained in a discharge tube. Vibronic analysis involving correlation of ion fundamental frequencies with those of parent molecules enables a detailed comparison to be made between the vibrational structure of the spectrum of the trichloro-ion and that of 1, 3, 5-C₆F₃H⁺₃. Analogous Jahn—Teller effects are shown to take place in the ground state of the two ions. The same linear coupling model is used and two possible solutions for D₆ and ω₆ are obtained by fitting the first two intervals in the 6^0,0_{v$\text{1}\text{2}$} progression in 1, 3, 5-C₆Cl ₃H⁺₃: (i) D₆ = 0.05 - 0.08, ω₆ = 455 - 447 cm^?1, (ii) D₆ = 0.39 - 0.49, ω₆ = 399 - 392 cm^?1. Arguments based on previously established criteria, and applied here to the case of the 1, 3, 5-C₆Cl₃H⁺₃ ion are given to select set (ii) as being far more satisfactory in interpreting the experimental data. Fitting to a larger number of bands gave D₆ = 0.45, ω₆ = 395 cm^?1. The Jahn—Teller potential energy barrier E^JT₆ = 178 cm^?1 is about three times greater than in the 1, 3, 5-trifluorobenzene ions, but sufficiently small for the dynamic Jahn—Teller effect to be operative in 1, 3, 5-C₆Cl₃H⁺₃. Some remarks are made concerning assignments in the excitation spectrum and matrix fluorescence analyses.     

Ion—molecule reactions of CH+3 with acetonitrile at thermal translational energies

The 0.1 eV translational energy reactions of CH⁺₃ and CD⁺₃ with acetonitrile were studied in a tandem Dempster-ion cyclotron resonance mass spectrometer. Channels leading to CH₃CNH⁺ (7%), H₂CN⁺ (58%), and C₂H⁺₅ (35%) were observed. For CD⁺₃ reactant ions the H₂CN⁺ and C₂H⁺₅ products show evidence of complete H, D isotopic scrambling, suggesting an intermediate complex.     

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.     

Equilibrium constants of HF,F-, HF-2 and H2F2 species in formic acid.

Equilibrium constants for the fluorinated species HF, F^-, HF^-₂ and H₂F₂ in formic acid and in a 1M potassium formate solution in formic acid have been studied by ¹⁹F NMR. The chemical shifts of these species have been determined from measurements of the shifts for various initial mixtures of differing concentrations of dissolved HF, F^- and HF^-₂. From these values, relative concentrations of HF, F^-, and HF^-₂ and H₂F₂ in each solution have been calculated through a numerical method. The following constants were obtained: K₁ = [H⁺][F^-]/[HF] = 1.1 x 10^-5M; K_D = [HF][F^-]/[HF^-₂] = 0.5 M; K′₁ = [H⁺][HF^-₂]/[H₂F₂]= 1.1 x 10^-5 M; K′_D = [HF]²/[H₂F₂]=0.5 M.     

CH3SO3裂解反应的机理和热力学性质

在G3XMP2//B3LYP/6-311+G(3df,2p)水平上对CH₃SO₃裂解反应的机理进行了研究, 获得了6 条通道(10 条路径), 并构建了其势能剖面. 同时采用单分子反应理论计算了各个通道在温度200-3000 K区间的速率常数. 研究结果表明, 在计算温度范围内, CH₃SO₃裂解反应的主产物为P1(CH₃+SO₃), 产物P2(CH₃O+SO₂)和P3(HCHO+HOSO)仅在温度大于3000 K时对总产物有贡献, 而产物P4(CHSO₂+H₂O), P5(CH₂SO₃+H)和P6(CHSO₃+H₂)贡献相对较少. 将裂解反应总的速率常数拟合为k_total=1.40×10¹²T^0.15exp(7831.58/T). 此外, 根据统计热力学原理, 预测了所有物种的生成焓(D_fH^Θ_{298 K}, D_fH_{0 K}), 熵(S^Θ_{298 K})和热容(C_p, 298-2000 K), 计算的结果与实验值较接近.     

The H2 elimination reactions of Ã2B3g C2H4+ and C2D4+

Kinetic energy releases from the unimolecular H₂ (D₂) elimination reactions of energy-selected òB_3gC₂H₄⁺(C₂D₄⁺) have been obtained by a photoelectron-photoion coincidence technique. The energy releases suggest a 1,1 elimination and are compatible with the presence of a small reverse activation energy barrier of the order of 0.02 eV. Such a barrier was indicated by a detailed ab initio study of this dissociation and the present results are discussed in the light of this theoretical treatment.     

A theoretical study of the sulphonium cation SH+3

Ab initio Hartree—Fock calculations with STO-3G functions have been performed to determine the structure (1.371 Å and 95.33°) of SH⁺₃ and the proton affinity (≈196 kcal/mol) of H₂S. Inclusion of a sulphur 3d function in the basis has been found essential to give a better geometry of SH⁺₃.