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Intramolecular isotope effects in the bond forming reactions following collisions of both CO&sup2+;[sub 2] and CF&sup2+;[sub 3] with HD have been investigated experimentally. For the CO&sup2+;[sub 2] + HD system the bond-forming pathway forming XCO&sup+; (X = H, D) exhibits a strong intramolecular isotope effect favoring the formation of DCO&sup+; at low collision energies. For the CF&sup2+;[sub 3] + HD system the bond-forming pathway forming XCF&sup+;[sub 2] also exhibits a strong intramolecular isotope effect favoring the formation of DCF&sup+;[sub 2] at low collision energies. However, in the CF&sup2+;[sub 3] + HD system a weak, and previously unobserved, channel, forming XF&sup+; exhibits no intramolecular isotope effect over the collision energy regime (0.2–0.5 eV) investigated. The absence of an intramolecular isotope effect in the formation of XF&sup+; casts doubt on the previous explanation of such isotope effects as resulting from orientation effects in the approach of the dication to the HD molecule. Using a recently proposed mechanism for the reaction of CO&sup2+;[sub 2] with H[sub 2], an analysis of the statistical and zero-point factors affecting the competition between the bond-forming channels is presented. This analysis shows that such factors can readily explain the intramolecular isotope effects observed in these reactive systems. [ABSTRACT FROM AUTHOR]

Using the photo-electron-product-ion-coincidence method (PEPICO) we have measured state-selective cross sections for the following processes: (A) N+2(X,A;v)+H2→N2H++H, (B) H+2(X;v)+N2→N2H++H, (C) N+2(X,A;v)+H2→H+2+N2, and (D) H2+(X;v)+N2→N2++H2. The measurements were performed at thermal velocities (Ec.m.≊40 meV). We have found that the charge transfer processes (C) and (D) have cross sections that are at least an order of magnitude smaller than the cross sections for the rearrangement processes (A) and (B). The cross section for reaction (A) with N2+(A;v) as reactant is found to be (50.2±2.4)% of the cross section for the same reaction with N2+(X;v) as reactant. The cross section for reaction (B) is found to be independent of the internal energy of the reactant ion. The measured variation of the cross sections as a function of the internal energy of the reacting ion is compared with calculations based on a RRKM type statistical model and an electronic correlation diagram of the (N2–H2)+ system. Excellent agreement is found, indicating complete randomization of internal energy within the collision complex. Absolute cross sections are determined for the rearrangement reactions: for reaction (A) the cross section is 76.1 Å2 starting with N2+(X;v=0,1) and 38.05 Å2 starting with N2+(A;v=0–5). For reaction (B) the cross section is 114 Å 2 for H2+(X;v=0–6). © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This article presents detailed internal and kinetic energy dependent cross sections and reaction rates for the hydrogen atom transfer processes N+2(X 2Σ+g, v+=0–4, J+=2)+H2→N2H++H, which were obtained under single-collision conditions in a guided-ion beam/scattering gas experiment. Preparation of ions in specific states relied on single-color excitation within a resonantly enhanced (2+1) multiphoton ionization scheme. The translational energy of the ions, Elab, was varied from 0.1 eV to approximately 30 eV. A small activation barrier impedes the reaction. Vibronic state preparation of the nitrogen ion is influential on the nature of the energy surface—N+2+H2 or H+2+N2—along which the H atom transfer proceeds. Calculations of model potential energy surfaces suggest that the reaction pathway must involve several exoergic and endoergic channels which open successively as the collision energy increases. A purely collision determined cross section—as would be evidenced by the E-1/2 dependence formulated in the Langevin–Gioumousis–Stevenson model—is observed only within a narrow window of kinetic energies. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Collisions of ground state N[sup +] ions with N[sub 2] were investigated in a Guided Ion Beam (GIB) apparatus at center-of-mass (CM) collision energies up to 10 eV. Isotopic labeling of the target gas, [sup 15]N[sub 2], was used as one criterion to distinguish electron transfer, atom transfer, and isotope exchange channels. The absolute cross sections are in good agreement with previous measurements. By combining the GIB technique with time-of-flight analysis (acronym GIB-TOF) more detailed information on the reaction dynamics has been obtained. The product velocity distributions measured for [sup 15]N[sub 2][sup +] and [sup 14]N[sup 15]N[sup +] indicate that both, electron and atom transfer, have to be divided into at least two parts, a direct one and one which seems to be characteristic for a long lived complex. The branching ratios derived for these four channels show a strong energy dependence. The mean product kinetic energy indicates that the remaining nitrogen atom is most probably formed in the metastable N([sup 2]D) state. For the nearly thermoneutral [sup 14]N[sup +]-[sup 15]N[sup +] isotope exchange it was observed that a significant fraction of the translational energy is transferred into internal excitation of the neutral molecule. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Integral cross sections for the bond-forming reaction CO[sup 2+]+Ar→ArC[sup 2+]+O have been measured as a function of collision energy in a guided-ion beam mass spectrometer. The energy dependence is consistent with an endoergic reaction. Since the title reaction is in competition with several charge-transfer processes, the cross section at the maximum is only 0.023 Å[sup 2] at a collision energy of about 3 eV. Simple kinematics considerations suggest that the falloff of the cross section at higher energies might be due to the vibrational predissociation of ArC[sup 2+]. State correlation diagrams are used for discussing the reaction mechanism. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]