T. F. Moran

Charge transfer reactions involving doubly-charged molecular ions

Abstract Electron transfer reactions between doubly-charged molecular ions and neutral molecules have been studied. Electron impact ionization of AB molecules (AB = N 2 , O 2 , NO, CO 2 , and I 2 ) has resulted in formation of stable, doubly-charged AB 2 + molecular ions which have been accelerated to keV kinetic energies and reacted with neutral target molecules to produce fast AB + molecular ions. Variations of AB + product ion intensities with ionizing electron energy are similar to previously measured ionization efficiency curves of AB 2+ reactant ions. Total cross sections measured for single electron transfer in N 2 2+ -AB reactions are relatively large. Large cross sections result from small energy defects and favorable vibrational overlaps for the charge transfer process N 2 2+ + AB → N 2 + + AB + .

Abinitio potential energy curves for the low‐lying electronic states of N22+

Potential energy curves have been calculated for N2(X 1Σg+), N2+(X 2Σg+), and for the low‐lying 3Σg−, 1Σg+, 3Πu, 1Πu and 3Πg states of N22+ using SCF techniques. Two different Gaussian basis sets were employed and N22+ curves were determined over a range of internuclear distance from 1.80 to 4.00 bohr. These curves were then used to calculate equilibrium internuclear distances, harmonic and anharmonic vibrational constants, and ionization potentials for the various N22+ states.

Vibrational deactivation of oxygen ions in low velocity 02+(X2Πg,υ=1)+02(X 3Σg−,υ=0) collisions

The deactivation of 02+(X 2Πg, υ=1) ions in collisions with 02(X 3Σg−,υ=0) molecules has been examined using multistate impact parameter eikonal and orbital treatments. Cross sections for the formation of various product states in the charge exchange and direct scattering channels have been computed for ions with 0.5 to 8.0 eV c.m. kinetic energies. The relative probabilities for forming products in given vibrational states at the higher kinetic energies are similar for the eikonal and orbital approaches. At energies below several eV it is necessary to employ the multistate orbital treatment which takes explicit account of the strong ion–molecule scattering. Cross sections for reaction channels leading to de‐excitation and/or excitation of the product 02+(X 2Πg,v=1) ions have been computed for both charge exchange and direct scattering processes. The channels leading to vibrationally deactivated 02+(X 2Πg, v=0) product ions are strongly favored at low velocities over the excitation processes in the charge...

Charge transfer reactions of ground C+(2P) and excited C+(4P) state ions with neutral molecules

Total charge transfer cross sections have been measured for the reactions of 0.7–2.5 keV C+(2P) and C+(4P) ions with Ar, H2, N2, CO, CO2, and O2. Time‐of‐flight techniques have been used to measure the fast neutral C0 products from charge transfer reactions. These reactions have been examined as a function of the electron energy used to produce the reactant ions and reaction cross sections determined for ground C+(2P) and excited C+(4P) state ions. Reactant C+ beams have been produced by controlled electron impact ionization of carbon monoxide. The cross sections for charge transfer reactions involving the excited C+(4P) ions are significantly larger than the corresponding reactions of ground state ions.

H+3 vibrational frequencies from ion impact spectroscopy

Abstract Inelastic energy losses in the collisions of H + 3 with Ne have been measured in a beam apparatus designed to direct mass analyzed, low energy ion beams onto target molecules and scan the energy, mass, and angular distributions of charged interaction products. The experimental energy loss spectra at small scattering angles correspond to that expected for vibrational excitation of H + 3 . Frequencies obtained from these inelastic energy loss data are found to agree with the quantum mechanical calculations of Christoffersen and of Schwartz and Schaad. Transitions involving doubly degenerate H + 3 bending modes are dominant under the conditions of these experiments.

Stable multiply charges molecular ions

Stable doubly ad triply charged molecules ions of the smallest heterocyclic aromatic compounds C4H4X (X=NH, O and S) have been observed. Ionisation energies have been measured and correlated with computed values. Structures, stabilities and vibrational frequencies for these multiply charged molecular ions were computed employing a self-consistent-field-molecular-orbital treatment. Stable structures found for these multiply charges ions possess charge distributed throughout each ion. Ionic binding energies of several eV have been calculated for these doubly and triply charged species.

Doubly-charged gas phase cations

Unique features of doubly-charged stable organic ions are examined and the results correlated with experimental observations. Self-consistent field molecular orbital methods are used to compute structures and stabilities of CnH22+(n=2–9) ions which are prominent in electron impact ionization of hydrocarbon molecules. A simple curve crossing model is employed to rationalize charge transfer reactions of these ions.

Structures, energetics and fragmentation pathways of CnH22+ carbodications

Potential energy curves have been calculated for CnH22+ (n = 2−9) ions and results have been compared with data on unimolecular charge-separation reactions obtained by Rabrenovic and Beynon. Geometry-optimized, minimum energy, linear CnH22+ structures have been computed for ground and low-lying excited states. These carbodications exist in stable configurations with well depths greater than 3 eV. Decomposition pathways into singly charged fragment ions lead to products with computed kinetic energies in excess of 1 eV. A high degree of correlation exists between experimental information and results computed for linear CnH22+ structures having hydrogen atoms on each end. The exception involves C4H22+ reactions where a low-lying doubly charged isomer must be invoked to rationalize the experimental data.

Collision‐induced dissociation of N2+ in X 2Σg+, A 2Πu and excited metastable states in N2+–N2 interactions

The collision‐induced dissociation of 0.65–5.0 keV N2+ has been examined in an apparatus with an extended flight path through which ions take a long time to travel. Short lived states in the reactant ion beam decay radiatively prior to reaction. Reactant ions have been produced in an electron impact ion source. Collision‐induced dissociation of N2+ has been studied as a function of the ionizing electron energy. Electronic and vibrational state distributions of reactant ions as functions of ionizing electron energy have been estimated from published spectroscopic data and the dissociation cross sections determined for N2+ (X 2Σg+,υ and A 2Πu,υ) ions. The relative contribution of a higher metastable ion state or states to the dissociative channels becomes more important as the incident ion kinetic energy is lowered. An energetic threshold of approximately 22.5±1.5 V has been measured for this long‐lived state leading to N+ in dissociative collisions.

Single- and double-electron transfer reactions of ground and metastable state Ar2+ ions

Electron transfer cross sections have been measured for reactions of Ar2+ ions with Ar, N2, O2, CO2, CH4 and C2H6. Time-of-flight techniques have been used to measure both fast neutral Ar0 and fast Ar+ products from single- and double-electron transfer processes involving Ar2+ ions with 4.0 to 7.0 keV impact energies. Incident Ar2+ ions have produced by controlled electron impact ionisation of argon atoms. Reactions have been examined as a function of ionising electron energy and cross sections determined for ground state Ar2+(3P) ions. Charge transfer cross sections have been determined to be in the range of 3*10-16 cm2 for the systems examined. Double-electron transfer cross sections are the same order of magnitude as those measured for the corresponding single-electron transfer reactions. The state distribution of the reactant ion beam has been estimated and electron transfer cross sections obtained for single- and double-electron transfer reactions of metastable Ar2+ ions. The magnitudes of electron transfer cross sections in individual systems are similar for both ground and metastable state Ar2+ reactions.