Reactions of excited and ground state H3+ ions with simple hydrides and hydrocarbons: collisional deactivation of vibrationally excited H3+ ions (original) (raw)
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Reactions of excited and ground state H3+ ions with methyl substituted hydrides
International Journal of Mass Spectrometry and Ion Physics, 1973
The reactions of H3 + with C,H6. CH3NH,. CH,OH, CH,F, CHsSH, and CH,CL have been studied using ion cyclotron resonance p&se ejection techniques. The product distribution obtained is strongly dependent upon hydrogen pressure due to a large difference in reactivity between excited and ground state II,+ ions. The H, i ions originally formed by the reaction of H,+ with H, are highly excited. At low hydrogen pressures, these excited H, f ions react mainly by direct processes: by charge transfer and by a process equivalent to hydride ion abstraction. The product distrib.ution changes as the hydrogen pressure is raised due to rapid deactivation of the Hsi ions by cohisions with H2 molecules. At intermediate hydrogen pressures, the hydride ion abstraction process disappears and both ground state and partially deactivated Hs+ ions react principaiiy by proton transfer to give a longer-lived protonated intermediate. With the exception of ethane, decomposition of the protonated intermediate occurs via vicinal hydrogen elimination and except for C&T&, CH,SH, and CH,CI, C-X bond scission to give the methyl cation is observed as weil. From the dependence of the relative rate for charge transfer on hydrogen pressure, evidence is obtained indicating that the excited H,+ ions may not be directly deactivated to the ground state but to some intermediate state(s) still containing a significant amount of internal energy, and that these intermediate H, f-ions are subsequently only very slowly deactivated to the ground state.
International Journal of Mass Spectrometry and Ion Physics, 1973
The proton transfer reaction of H3+ ions with CH,NH2, CH,OH and CH,SH produces the excited intermediatecomplexes [CH3NH3i]*, [CH30H2']), and [CH,SH2+ ]* which subsequentIy decompose in two ways: by vicinai hydrogen elimination, and by C-X bond scission to give the methyl cation. The condensation reaction of methyl cations with NH,, H20, and Hz!3 is the reverse of the latter decomposition pathway and proceeds to give the same excited intermediates followed also either by vicinal hydrogen elimination or by back reaction. The Hi3 i ions formed by reaction of Hz+ with Hz are highly excited, and the presence of excess internal energy in the H, i-ion is shown to be a critical factor in the ratio of decomposition products obtained. A detailed analysis of the deactivation of * Supported by the National Science Foundation Grant No_ GP-15628 and by Contract NO. NAS 7-100 sponsored by the National Aeronautics and Space Administratioti. * D. K. Bohme (personal communication) used the flowing afterglow technique to measure the proton affinity of Hz as 4.71 e\! reiative to methane. The proton afkity of' CH, has recently been determined by photoionization~" as 5.50 eV. Cotton et al.* obtained 4.37 eV for the proton afiknity of Hz..
The effects of collision energy and vibrational excitation on H+2, HD++He reactions
The Journal of Chemical Physics, 1984
An experimental study of proton and deuteron transfer in H+2 + He and HD+ + He has been carried out as a function of kinetic and vibrational energy. The data gives evidence that at lower kinetic energies, the spectator stripping mechanism indeed plays an important role when H+2 or HD+ is vibrationally excited. The H+2 (v=0) reaction has a much smaller cross section than the v=1–4 reactions and seems to go through intimate, small impact parameter collisions involving all the atoms. Investigation of the competition between both the proton and deuteron transfer channels for the HD+ case, shows that vibrational enhancement towards forming the HeD+ product falls off sooner with increasing kinetic energy than does the HeH+ product again in accordance with the spectator stripping model. The higher yield for HeH+ production at both higher vibrational levels of HD+ and at lower kinetic energy and the behavior of translational energy dependence of HeH+ seems to indicate the importance of the ...
Ion-molecule reactions in H2/rare-gas systems by ion cyclotron resonance I. Reactions with He and Ne
International Journal of Mass Spectrometry and Ion Physics, 1976
reactions is of interest because they are simple enough to be treated theoretically in some cases, and becltuse they provide a useful basis for interpreting more complex reactions_ Additionally* the heats of formation of ail reactants and products are w=ll known [ 1) permittins a better understandins of the details of these reactions-The most recent study of rare-_-hydrogen systems is that of Ryan and Graham [2 ] who used an ion-trapping technique to investigate the thermaleneqy reactions-Rate constants were determined from disappearance of primary and secondary ions under conditions of very high conversion, Interpretation of their resuhs is compliuted by the fact that the rates of reaction of H,' with He and Ne depend stron$y on Hz* vibrationaklevei distributions p] which may be altered
Mechanism for the destruction of H3 + ions by electron impact [3]
Nature, 2001
The rate at which the simplest triatomic ion (H + 3 ) dissociates following recombination with a low-energy electron has been measured in numerous experiments 1±10 . This process is particularly important for understanding observations of H + 3 in diffuse interstellar clouds 11±13 . But, despite extensive efforts , no theoretical treatment has yet proved capable of predicting the measured dissociative recombination rates at low energy, even to within an order of magnitude. Here we show that the Jahn±Teller symmetry-distortion effect 16±19 Ðalmost universally neglected in the theoretical description of electron±molecule collisionsÐgenerates recombination at a much faster rate than any other known mechanism. Our estimated rate constant overlaps the range of values spanned by experiments. We treat the low-energy collision process as a curve-crossing problem, which was previously thought inapplicable 20 to low-energy recombination in H + 3 . Our calculation reproduces the measured propensity for three-body versus two-body breakup of the neutral fragments 3 , as well as the vibrational distribution 4 of the H 2 product molecules.
Collision processes of C2,3Hy and C2,3Hy+ hydrocarbons with electrons and protons
Physics of Plasmas, 2004
Cross sections and rate coefficients are provided for inelastic collision processes of electrons and protons with C x H y and C x H y ϩ (xϭ2,3; 1рyр2xϩ2) hydrocarbon species in a wide range of collision energies and plasma ͑gas͒ temperatures. The considered processes include electron-impact ionization and dissociation of C x H y , dissociative excitation, ionization and recombination of C x H y ϩ with electrons, and both charge transfer and atom exchange in proton channels are considered separately. The presented cross sections are based upon a critical assessment of available experimental data and upon an extensive use of a number of semi-empirical, physically well grounded cross section scaling relationships. Information is also provided for the energetics of each individual reaction channel. The cross sections and rate coefficients are presented in compact analytic forms.
Vibrational excitation of H2 and HCl by low-energy electron impact. An isotope scaling law
Chemical Physics Letters, 1992
We examine the mass dependence of cross sections for resonant vibrational excitation by electron impact (from z+ to ur) in H2 and its isotopes. Excitation cross sections, for both inelastic and superelastic collisions, using numerical potential curves in a nonlocal resonance theory are presented and seen to obey the scaling law ucc,~~"~-"~~~*, where n is the reduced nuclear mass of the isotope. This scaling law is also observed to hold for HCI, DCI, and TCl. We also present a supporting analytical argument for this isotope scaling law using a simple resonance model in which the neutral and resonant anion nuclear potential energy curves are taken as equal-frequency linear harmonic oscillators. Cross sections for vibrational excitation by lowenergy electron impact of Hz [ l-5 ] and of HCl [ 6-9] have been measured by several different investigators. The absolute cross section values for excitation from the y = 0 level of Hz are fairly consistent with each other to within 20%30%. Vibrational excitation of the heavier isotopes of H2 and HCl has been much less studied experimentally. Vibrationally excited D2 and other isotopes of H2 are of interest as a source of production of negative ions Hand D-through the process of dissociative electron attachment. It is therefore desirable to understand the dependence of vibrational excitation cross sections on the isotope mass. The purpose of this paper is to present an isotope scaling law for vibrational excitation of H2 and its isotopes from an arbitrary low-lying vibrational level. We also observe that this relationship holds approximately for the family of isotopes XCl, where X is one of H, D, or T. The cross sections are obtained by treating vibrational excitation as a resonant process which occurs through the formation of a temporary anion state, and numerically solving the nonlocal integrodifferential
Ion cyclotron resonance study of the ion-molecule reactions in methane-ammonia mixtures
Journal of the American Chemical Society, 1970
The ion-molecule reactions of ions formed by electron impact in methane-ammonia mixtures have been studied by ion cyclotron resonance (icr) techniques, and a number of charge transfer, proton transfer, hydro-(1) This paper presents the results of one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract No. NAS 7-100, sponsored by the National Aeronautics and Space Administration. (2) NASA Resident Research Associate, 1968-1969. (3) P. Ausloos, Ed., "Fundamental Processes in Radiation Chemistry,"