The transverse diffusion of mass-identified N+2 ions in nitrogen

A new apparatus suitable for the quantitative study of the transverse diffusion of mass identified ions is described. Measurements of the transverse diffusion of N⁺₂ in nitrogen are reported and comparison is made with other data.     

Theoretical study of the molecular ions SiH−5 and SiH−3

Ab initio HF and Cl calculations were performed to determine the equilibrium geometry of SiH^?₅ and SiH^?₃, the barrier for internal rotation (SiH^?₅) and inversion (SiH^?₃) and the stability of SiH^?₅ and further to study the effect of electron correlation on reaction energies. The gaussian-type basis included d and f functions on Si and a p set on II. The D_3h structures of SiH^?₅ is lower in energy than the C_4v structure by 2.9(3.2) kcal/mol (corresponding HF results in parentheses). SiH^?₃ has C_3v structure, the inner-ion barrier computed is 26.2 (27.3) kcal/mol. SiH^?₅ turns out to be stable with respect to SiH₄ + H^? by 20.3 (13.8) kcal/mol, but it is unstable with respect to SiH^?₃ ← H₂ by 6.3 (5.6) kcal/mol. These results show that electron correlation has a small effect on barriers of inversion (SiH^?₃) or pseudorotation (SiH^?₅), but may have a pronounced effect on reaction energies even if all systems involved have closed shells. The correlation energy contributions are analyzed in terms of intrapair and interpair terms in order to get a better understanding of the influence of correlation on reaction and activation energies.     

Laser-induced fluorescence in N2 and N+2 by multiple-photon excitation at 266 nm

The fluorescence transitions corresponding to the second positive system of N₂ (C³Π_u → B³Π_g) for Δv = 0, 1 and the first negative system of N⁺₂(B²Σ⁺_u → X²Σ⁺_g) for Δv = 0, 1, 2 have been observed following laser-induced mul excitation of N₂.     

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.     

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.     

Reactions of O+4 and O+2 with methane

Rate coefficients and products were determined for the title reactions employing a drift tube mass spectrometer apparatus. The implications of these reactions for the ion chemistry of the stratosphere is discussed.     

Excitation and decay of the C2Σ+u state of N+2 following collisions of He+ ions with N2 isotopes

A quantitative analysis is made of the N⁺₂ “2nd negative” emission (“2N”: C²Σ⁺_u → X²Σ⁺_g) produced by the impact of 500 eV to 25 keV He⁺ beams on ¹⁴N₂, ¹⁴N¹⁵N and ¹⁵N₂. Above about 5 keV, the relative 2N emission rates from the various vibrational levels of the C state are the same as those observed for ? 2 keV Ne⁺, or > / 90 eV electron-impact. These limiting distributions are compared to those predicted for a Franck-Condon excitation of the C state, modified by configuration interaction. The weakening in 2N emission at the vibrational levels ν′ > / 3 is ascribed to spontaneous C-state predissociation. The data fully confirm recent reports that this predissociation extends over a wide range of ν′ and that it is subject to a strong isotope effect. The ratios of the rates of C-state predissociation to 2N emission are obtained for the levels ν′ = 3 to 8 of each nitrogen isotope. By means of these data it is shown that near-resonant charge transfer dominates the distribution of vibrational excitation probabilities only at energies below about 10 eV. A comparison is made of absolute cross-sections for C-state emission with those for N⁺ and N⁺₂ production in He⁺/¹⁴N₂ collisions at energies between 5.5 eV and 25 keV.     

The SO+2 radical-ion

From the complex overall EPR spectrum of ⁶⁰Co gamma-irradiated pure solid sulfur dioxide the spectrum of the SO⁺₂ radical-ion was selected and the following principal values for the g-tensor obtained: g₁ = 1.9620;g₂ = 2.0026;g₃ = 2.0118 (Δg = ± 0.0005).     

Extension of the meinel system of N+2 to high vibrational levels of the A 2Πu state

The emission from long-lived excited states in a nitrogen ion beam has been analyzed for wavelengths between 4800 and 6000 A. Many of the observed feat     

Laser-induced fluorescence measurement of the nascent rotational distribution of N+2 (X2Σ+g) formed by electron impact on N2

The internal state distribution of ground state N⁺₂ ions formed from N₂ by electron impact ionization is measured under collision-free conditions using laser-induced fluorescence. Analysis of the B–X (0, 0) band shows the rotational distribution to be characterized by a temperature which increases slightly with decreasing electron energy (60–100 eV). Cascade contributions are unimportant.     

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.     

Explanation for the structural differences of S2+4, S04 and S2−4

An explanation for the geometry changes upon successive double reductions of S²⁺₄ (square planar, D_4h symmetry) to neutral S₄ (for which the structure is unknown) and finally to S^2?₄ (non-planar, C₂ symmetry) is given on the basis of orbital eigenvalues and wavefunctions calculated with the self-consistent-field Xα scattered-wave molecular orbital method.     

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.     

Vibration intervals for tritiated H+3 and D+3

Ab initio calculated values of fundamental vibrational frequencies and zero-point energies are presented for HTD⁺, D₂T⁺, T₂D⁺, H₂T⁺, T₂H⁺ and T⁺₃.     

Participation of incident ion internal energy in molecular O+2-Ar charge-transfer collisions

The O⁺₂—Ar charge-transfer reactions have been investigated for both the X²Π_g and a⁴Π_u states of O⁺₂ in the kinetic energy range of 0.7 to 3.0 keV. Exhibited resonant and non-resonant behavior of the cross sections is consistent with theoretical predictions.     

Ab initio calculations of the stability of the NH+5 ion

Some fragments of the NH⁺₅ potential surface have been calculated by the SCF MO LCAO method using a basis of linear combinations of gaussian lobe functions. The NH⁺₅ ion was found to be stable against dissociation into NH₃ and H⁺₂ or NH⁺₃ and H₂. Its stability with respect to decomposition into NH⁺₄ and H remains to be seen.     

On the structure of the NH+4 ion in aqueous solution

X-ray diffraction data from a 3.5 M solution of (NH₄)₂SO₄ and a 1.5 M solution of NH₄ClO₄ were examined. A model, in which NH⁺₄ ions are eight-coordinated with the N-H₂O distance 3.00–3.05 A, is consistent with experimental data, but there are insufficient reasons to prefer such a model to another in which NH⁺₄ ions simply replace H₂O molecules in the unchanged solvent structure.     

Pseudopotential calculations on Rb+2, Cs+2, RbH+, CsH+ and the mixed alkali dimer ions

Semi-empirical pseudopotentials are used in calculating the ground-state potentials curves for single valence-electron molecular ions. Very accurate results are obtained and a number of predictions given. The ionization energies of the neutral dimers are evaluated. A spectroscopic rule enables us to estimate the A ¹Σ⁺ state of KRb and RbCs.     

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.     

The laser sensitized reaction SF26 + NO + O3

A pulsed CO₂ laser was used to irradiate a rapidly flowing mixture of NO, O₃, and SF₆. When the laser was tuned to an SF₆ absorption line, an increase in the visible NO^*₂ emission was observed. The laser-induced signal has two unusual features. First, the rise time is much longer than is observed when O₃ is excited directly, and, second, the signal decays to a value above the original baseline. The rise rate is attributed to VV energy transfer from SF²₆ to O₃, while the baseline shift is attributed to a temperature jump resulting from rapid non-resonant VV relaxation within the SF₆ molecule. Both the size of the T-jump and the fraction of vibrationally excited ozone molecules vary inversely with NO pressure.