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We have studied the dissociation dynamics of NO+ ions in their ground, X 1Σ+, and first excited metastable, a 3Σ+ states, induced by the capture of electrons of variable collision energy in the dissociative recombination (DR) process. The branching over the different dissociation channels has been measured in a merged-beam experiment on the heavy-ion storage ring, CRYRING. In accord with previous observations, NO+ (X 1Σ+,v=0) ions dissociate dominantly to the N(2D)+O(3P) product limit at 0 and 1.2 eV collision energies. In contrast to earlier reports, the spin-forbidden N(4S)+O(1D) dissociation limit contributes 0(±2)% at 0 eV. At 5.6 eV a new channel coupled to the production of ground-state atoms becomes more important, but no increase in the production of ground-state product atoms was observed. All observed branching fractions compare very favorably with predictions from a simple statistical model, which is based on the multiplicity of each dissociation limit in combination with spin conservation duri...

This paper presents a study of the dissociative recombination of C3H7+ with electrons in a heavy-ion storage ring, CRYRING. Cross sections were measured as a function of kinetic energy and found to be extremely rapid with a dependence of E-1.10±0.01. The recombination cross section was integrated to yield a thermal rate coefficient of 1.9 × 10-6 cm3 s-1. Product branching ratios were measured and proved to be quite complex. Although 16 channels are energetically accessible at 0 eV, it was not possible to assign branching ratios to all channels; some related channels were combined in the analysis. The results show that the dissociation channel corresponding to loss of a single hydrogen atom dominates, with a branching ratio of 0.42. Multiple H-loss channels are also observed. Product channels that involve breaking a C−C bond have a combined branching ratio ranging from 0.34 to 0.39.

Dissociative recombination (DR) of the water cluster ion D+(D2O)2 has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). Cluster ions were injected into the ring and accelerated to an energy of 2.28 MeV. The stored ion beam was merged with an almost monoenergetic electron beam, and neutral fragments produced by DR were detected by an energy-sensitive surface barrier detector. The first experimental determinations of the absolute DR cross section and branching ratios for a cluster ion are reported. The cross section for the process D+(D2O)2+e− is large and reaches 6⋅10−12 cm2 at a low center-of-mass collision energy of 0.001 eV. The cross section has an E−1.19±0.02 dependence in the energy range 0.001–0.0052 eV, and a steeper slope with an E−1.70±0.12 dependence for E=0.052–0.324 eV. The general trends are similar to the results for previously studied molecular ions, but the cross section is higher in absolute numbers for the cluster ion. Thermal rate coef...

We have studied the vibrationally relaxed C2H + ion in the heavy - ion storage ring CRYRING in Stockholm. We measured the dissociative recombination absolute cross section over center-of-mass energies in the range between 0 and 0.1 eV by scanning the electron energy. The rate of dierent neutral product channels of dissociative recombination was measured. We found the three-body chan- nel C2H + H + H, with a branching ratio of 59%, to be the dominant one. Finally, we compare C2H + and C2H + (Derkatch et al. 1999) results.

The dissociative recombination (DR) of HCNH+ has been studied at the heavy ion storage ring CRYRING. The absolute cross-sections have been measured between 0.01 meV and 0.2 eV collision energy. The DR thermal rate coefficients, which can be directly applied to modeling environments in thermal equilibrium, have been found to be 2.8 × 10-7(300/T)0.65 at temperatures T < 1000 K. The DR branching fractions have been measured for different dissociation channels: HCN(HNC)+H (0.67), CN+H2 (0.0), and CN+H+H (0.33) at collision energy of 0 eV. The results show that DR of HCNH+ is an efficient process leading to formation of HCN or HNC isomers, whereas CN production is dominated by three-body fragmentation. The multireference self-consistent calculations in a complete active space have been used as a common background for all studied species and reaction paths. Three-body fragmentation CN+H+H has been considered in one concerted elementary reaction step.

We present experimental data on the dissociative recombination (DR) and the dissociative excitation (DE) of O2+ in its electronic and vibrational ground state using a heavy ion storage ring. The absolute DR cross section has been determined over an electron collision energy range from 1 meV to 3 eV. The thermal DR rate coefficient is derived; α(Te)=2.4×10−7(300/Te)0.70±0.01 cm3 s−1, for T>200 K. The threshold for DE was observed near its energetic threshold of 6.7 eV. The DE cross section curve has a maximum of 3×10−16 cm2 near 15 eV. We have determined the branching fractions to the different dissociation limits and present atomic quantum yields for the DR process between 0 to 300 meV collision energy. The quantum yield of O(1D) is found to be 1.17±0.05, largely independent of the electron energy. Arguments are presented that the branching fraction to O(3P)+O(1S) is negligible. The branching fraction to the O(1S)+O(1D) is smaller than 0.06 and varies strongly as a function of collision energy. The O(1S) quantum yield is a strong function of electron temperature. Hence, the relative strength of the green, O(1S), and the red, O(1D), airglows may be used as a measure of the electron temperature of the upper atmosphere. A qualitative explanation is given of the consequences of nonadiabatic interactions in the dissociation step of the DR process.

Dissociative recombination of the polyatomic ions D3O+ and H3O+ with electrons have been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). Absolute cross sections have been determined from 0.001 eV to 0.25 eV center-of-mass energy for D3O+ and from 0.001 eV to 28 eV for H3O+. The cross sections are large (7.3×10−13 cm2 for D3O+ and 3.3×10−12 cm2 for H3O+ at 0.001 eV). At low energies, the cross sections for D3O+ are E−1 energy dependent whereas it is slightly steeper for H3O+. A similar E−1 energy dependence was also observed by Mul et al. [J. Phys. B 16, 3099 (1983)] with a merged electron-ion beam technique for both H3O+ and D3O+ and by Vejby-Christensen et al. [Astrophys. J. 483, 531 (1997)] with the ASTRID storage ring in Denmark, who presented relative cross sections for H3O+. A resonance has been observed around 11 eV for H3O+. It reflects an electron capture to Rydberg states converging to an excited ionic core. A similar structure was reported by Vejb...

Resonant ion pair formation from collisions of electrons with ground state diatomic molecular ions has been observed and absolute cross sections measured. The cross section for HD+ is characterized by an abrupt threshold at 1.9 eV and 14 resolved peaks in the range of energies 0 less than or equal to E less than or equal to 14 eV. The dominant mechanism responsible fbr the structures appears to be resonant capture and stabilization, modified by two-channel quantum interference. Data on HF+ show structure correlated with photoionization of HF and with dissociative recombination of electrons with this ion.

Absolute cross sections and rate coefficients were measured for the dissociative recombination of CN+(X 1Σ+ and a 3Π, ν=0) with electrons using the heavy ion storage-ring CRYRING at Stockholm University. The a 3Π state that lies only 0.08 eV above the X 1Σ+ ion ground state is most certainly populated in the ion beam injected into CRYRING, as this is a long-lived excited state. Over the 1 meV–3 eV energy range that was investigated, two energy dependencies were found for the cross sections, namely E−1.05 below 0.1 eV and E−1.41 above 0.4 eV. The energy domain 0.1–0.3 eV exhibits a resonant structure. Branching fractions over the final atomic product states were determined using a position sensitive imaging detector. Thermal rate coefficients are deduced from the measurements and the efficiency displayed by the dissociative recombination mechanism is typical of that of a diatomic ion (3.4×10−7 cm3 s−1 at room temperature). Cross sections for the dissociative excitation process are also reported and their m...

The absolute cross section and branching ratios for dissociative recombination of CH -->+2 with electrons have been measured by means of the heavy-ion storage ring CRYRING. Contrary to what has been previously believed, recombination of CH -->+2 is dominated by the three-body channel C + H + H (63%), whereas breakup into the CH + H and C + H2 channels occurs with branching ratios of 25% and 12%, respectively. The thermal rate coefficient for dissociative recombination at 300 K is 6.4 × 10-7 cm3 s-1, which is higher by a factor of 2.5 than the value used in modeling dark molecular clouds. The low CH production and the high production of energetic carbon atoms could be favorable factors for the turbulence model to explain the large abundance of interstellar CH+. The cross section for dissociative excitation was also measured and found to be in good agreement with results from a crossed electron-ion beam experiment.

Absolute cross sections and rate coefficients have been determined for dissociative recombination of electrons and ${\mathrm{CO}}^{+}$ ions for energies from 1 meV to 54 eV. We found values of $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ ${\mathrm{cm}}^{2}$ at 1 meV and ${10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}$ at 1 eV, with an essentially $1/E$ energy dependence. Branching ratios over the final atomic product states have been determined using a position- and time-sensitive imaging system. At zero eV collision energy the predominant yield is to ground-state atomic fragments (76%). At higher collisional energies the branching ratio to the ground-state limit is reduced. A new limit, $\mathrm{O}{(}^{1}D)+\mathrm{C}{(}^{1}D),$ opens up and branching to the $\mathrm{O}{(}^{3}P)+\mathrm{C}{(}^{1}D)$ limit increases. Cross sections are also determined for dissociative excitation of ${\mathrm{CO}}^{+}.$ Thermal rate coefficients are deduced from the dissociative recombination (DR) data, and compared with measurements in the literature. Consideration of both the theoretical and spectroscopic data in the literature giving information about the potential curves along which DR may take place reveals both a paucity and disparity of the data.

The heavy-ion storage ring CRYRING was used to measure the absolute dissociative recombination and dissociative excitation cross sections for collision energies below 50 eV. Deduced thermal rates coefficients are consistent with previous beams data but are lower by a factor of 3 than the rates measured by means of the flowing afterglow Langmuir probe technique. A resonant structure in dissociative recombination cross section was found at 9 eV. We have determined the branching fractions in DR of CH+5 below 0.2 eV. The branching is dominated by three-body CH3 + H + H and CH2 + H2 + H dissociation channels, which occur with branching ratios of ≈ 0.7 and ≈ 0.2, respectively; thus methane is a minor species among dissociation products. Both the measured absolute cross sections and branching in dissociative recombination of CH+5 can have important implications for the models of dense interstellar clouds and abundance of CH2, CH3 and CH4 in these media.

The absolute dissociative recombination and absolute dissociative excitation rate coefficients and cross sections have been determined for N⊃+⊃2 and electrons for collision energies between 10 meV and 30 eV. The ion storage ring CRYRING has been used in combination with an imaging technique with a position-and-time-sensitive detector. Information is retrieved on the ion beam vibrational state populations and on the product branching in the dissociative recombination process at 0 eV collisions. A hollow cathode ion source has been used to lower the vibrational excitation in the ion beam; a more traditional hot-cathode ion source was used as well. The most important findings are the following. The rate coefficient for an N⊃+⊃2 ion beam (46%, v = 0, 27% v = 1) versus electron temperature (K) is α(Tc) = 1.75(±0.09) x 10-7(Tc/300)-0.30 cm3 s-1. The dissociative recombination rate is found to be weakly dependent on the N⊃+⊃2 vibrational level. At 0 eV collision energy, the v = 0 product branching is found to be 0.37(8):0.11(6):0.32(4) for N(4S) +N(2D):N(⊃2⊃P)+N( 4S):N(⊃2⊃D)+N(⊃2⊃D) fragments. The dissociative recombination cross section does not have a high-energy peak as was found in a number of lighter molecular systems. The dissociative excitation signal starts only slightly above the energy threshold for dissociation, and peaks near 25 eV. From the dissociative excitation data and literature data, information is retrieved on the dissociative ionization of N⊃+⊃2. The comparison of these results with earlier DR measurements is extensively discussed. © 1998 American Institute of Physics.

Dissociative recombination and excitation of D3+ have been studied in CRYRING, a heavy-ion storage ring at the Manne Siegbahn Laboratory at Stockholm University. The measured cross section for dissociative recombination was used to deduce a 300 K rate constant of 2.7 × 10-8cm3s-1. This is a factor of four smaller than the corresponding value for H3+ measured earlier in CRYRING. Dissociative excitation into both the D and 2D channels (D + D or D2) were studied. The 2D channel occurs at energies below threshold for the ion's dissociative states, which indicates that resonant enhanced dissociative excitation via autoionizing resonances takes place.

The heavy-ion storage ring CRYRING at the Manne Siegbahn Laboratory at Stockholm University has been used for the study of dissociative recombination of 3HeH+. The new adiabatically expanded electron beam at CRYRING, which is achieved by means of a superconducting magnet, was used. The electron-beam expansion factor of 100 gave a transverse electron temperature of about 1 meV. This allowed the observation of several new resonances in the recombination cross-section.

A microchannel plate/CCD-camera particle detector is described that utilises gold strips deposited upon the surface of a MCP to provide particle arrival time information. The uncertainty in the timing is assessed to be ∼500 ps (FWHM) for a measured time interval between adjacent strips. The main contribution of which is the result of the slow response time of the CFD compared to the signal. The application of timing measurement is shown to be of particular benefit in the accurate determination of product state branching ratios from the dissociative recombination of diatomic ions. Finally, the possibilities of such a detector are assessed.

Dissociative recombination of vibrationally cold has been studied at the ion storage ring CRYRING, with an accurate measurement of the kinetic energy of the recombination fragments. When the incident electron energy exceeds , fragments are observed with a kinetic energy of only . The energetics suggest that this low-energy channel derives from either recombination of the state or recombination of the metastable state. High-quality ab initio calculations have been used to obtain the state vibrational relaxation time (10 ms), excitation energy (2.25 eV) and radiative lifetime (0.030 s). The dissociative recombination cross section has been obtained in a model calculation. The results imply that the state has too small a recombination cross section and too short a radiative lifetime to explain the experimental results, which were obtained after 15 s of storage in CRYRING. We conclude that the 120 meV channel is due to recombination of into the asymptotic limit. Possible mechanisms are discussed.

The cross section for dissociative recombination of vibrationally cold ${\mathrm{D}}_{3}^{+}$ has been measured at the ion storage ring CRYRING. The rate constant at 300 K, $\ensuremath{\alpha}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}{\mathrm{cm}}^{3}{\mathrm{s}}^{\ensuremath{-}1}$, is a factor of 4.3 smaller than the corresponding value for ${\mathrm{H}}_{3}^{+}$ measured earlier in CRYRING. An electric field of 30 V/cm was introduced in the electron-ion interaction region. This had no measurable effect on the dissociative recombination cross section. This suggests that the cross sections measured in storage rings for ${\mathrm{H}}_{3}^{+}$ and its isotopic variants can be directly compared with theoretical results once such results become available.

We report experiments on dissociative recombination (DR) of HD{sup +} and H{sub 2}{sup +}. Product state information has been obtained over a wide range of electron energies with a position sensitive detector consisting of a graded absorber in combination with a surface-barrier detector. At low electron energies ({lt}3 eV) hydrogen atoms are formed preferentially in highly excited states ({ital n}{gt}2); at high electron energies ({gt}12 eV) both hydrogen fragments are excited. The dissociative recombination rate of H{sub 2}{sup +} has been measured also as a function of storage time in the energy range of 0 eV to 20 eV. We show that the H{sub 2}{sup +} beam is still vibrationally excited after 20 s at our experimental conditions. The H{sub 2}{sup +} ions relax vibrationally through interaction with electrons in the electron cooler. Vibrationally excited levels ({ital v}{ge}5) have DR rates that exceed the DR rate of the lower vibrational levels by two orders of magnitude. The latter observation has important consequences for the interpretation of previous DR experiments on H{sub 2}{sup +}. {copyright} {ital 1996 The American Physical Society.}

Absolute cross sections have been determined for the dissociative recombination and dissociative excitation of $^{4}\mathrm{HeH}^{+}$ for electron energies below 40 eV. The dissociative recombination cross section is in semiquantitative agreement with recent theoretical results by Sarpal, Tennyson, and Morgan [J. Phys. B 27, 5943 (1994)] and Guberman [Phys. Rev. A 49, R4277 (1994); in XIXth International Conference on the Physics of Electronic and Atomic Collisions, Whistler, Canada, AIP Conf. Proc. No. 360, edited by L. J. Dube, J. B. A. Mitchell, J. W. McConkey, and C. E. Brion (AIP, New York, 1995), p. 307]. The calculated resonant structure below a collision energy of 1 eV was not fully reproduced by the experiment. The quantum states of the dissociative recombination products at 0 eV collision energy have been determined; ground-state helium and excited hydrogen atoms (n=2) are dominantly formed, in agreement with recent predictions by Guberman. The dissociative excitation has an onset around 10 eV and follows the shape of the dissociative recombination cross section, illustrating that both processes start with the formation of doubly excited neutral states that lie in the ionization continuum as well as in the dissociation continuum. The dissociative excitation cross section is in quite good agreement with recent calculations by Orel and Kulander. \textcopyright{} 1996 The American Physical Society.

The dissociative recombination (DR) of CH{sub 5}{sup +} and CD{sub 5}{sup +} has been studied at the heavy-ion storage ring CRYRING. The fragmentation dynamics of the dominant reaction channel CH{sub 3}+H+H has been investigated using an imaging detector. The results indicate that a two-step process via the production of a CH{sub 4} intermediate, which has sufficient energy to fragment further to CH{sub 3}+H, may play an important role. Discrepancies between the present and earlier results obtained from storage ring measurements with those from flowing afterglow experiments are addressed. Newly measured branching fractions in the DR of CD{sub 5}{sup +} show an excellent agreement with branching fractions previously measured for CH{sub 5}{sup +}, and the absolute DR cross sections have been also measured over an interaction energy range between {approx}0 and 0.1 eV for both isotopologs.

We have studied the dissociative recombination (DR) of molecular hydrogen ions with slow electrons over a range of collision energies from 0 to 400 meV. By employing a pulsed expansion source for rotational cooling and by exploiting super elastic collisions with near-0-eV electrons in a heavy ion storage ring for vibrational cooling, we observe a highly structured DR cross section, comparable to that reported for HD+. Using para-hydrogen-enriched ion beams, we identify for the first time features in the DR cross sections attributed to nu=0, J=even molecules (para-H2) and nu=0, J=odd (ortho-H2) molecules, separately. Indications are given that para levels have different DR rate coefficients from ortho levels for the first four vibrational levels at near-0-eV collisions.

The dissociative recombination (DR) process of NH4+ and ND4+ molecular ions with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). The absolute cross sections for DR of NH4+ and ND4+ in the collision energy range 0.001-1 eV are reported, and thermal rate coefficients for the temperature interval from 10 to 2000 K are calculated from the experimental data. The absolute cross section for NH4+ agrees well with earlier work and is about a factor of 2 larger than the cross section for ND4+. The dissociative recombination of NH4+ is dominated by the product channels NH3+H (0.85+/-0.04) and NH2+2H (0.13+/-0.01), while the DR of ND4+ mainly results in ND3+D (0.94+/-0.03). Ab initio direct dynamics simulations, based on the assumption that the dissociation dynamics is governed by the neutral ground-state potential energy surface, suggest that the primary product formed in the DR process is NH3+H. The ejection of the H atom is direct and leaves the NH3 molecule highly vibrationally excited. A fraction of the excited ammonia molecules may subsequently undergo secondary fragmentation forming NH2+H. It is concluded that the model results are consistent with gross features of the experimental results, including the sensitivity of the branching ratio for the three-body channel NH2+2H to isotopic exchange.

Much recent work in the field of dissociative recombination (DR) has been related to the break-up of polyatomic ions since, in spite of the apparent simplicity of DR, developing a general theory to predict product branching ratios for even the simplest polyatomic ions, e.g. X H 2 + , has proven to be difficult. Early models suggested that such ions would predominantly fragment to H + XH. However, all recent storage ring studies for such ions show a propensity for three body breakup, i.e. X + H + H.1−4 In the last year, the dynamics of some of these systems have been investigated, with results reported for H2O+ 5 and H 3 + ,6 and a brief review was also published.7 Using trajectory calculations, we have also investigated the dynamics on some of the potential surfaces involved in the DR of H2O+.8 The group at TSR looked at the dynamics in, and competition between, the two and three body fragmentation dynamics of H 3 + . Using a statistical model,9 they reached good agreement with the experimental data previously obtainedat CRYRING1 as a function of reaction energy.

We report an investigation into the three-body fragmentation of a triatomic molecule ${\mathrm{H}}_{2}\mathrm{O}$ via the process of dissociative recombination (DR) of ${\mathrm{H}}_{2}{\mathrm{O}}^{+}.$ At 0-eV center-of-mass reaction energy two competing three-body fragmentation channels are available, both leading to the production of ground state H atoms $\mathrm{H}{(}^{2}S)$ but differing in the excitation state of the O atom fragment: $\mathrm{O}{(}^{3}P)$ and $\mathrm{O}{(}^{1}D).$ Using time- and position-sensitive detectors in a triple-coincidence experiment, the fragments from the DR reaction are monitored and their momentum vectors and angular distribution recorded. From these data we determine that during the recombination process, oxygen atoms are produced in the ratio of 3.5(0.5):1 for $\mathrm{O}{(}^{3}P):\mathrm{O}{(}^{1}D),$ and find that the molecular geometry is not conserved and that the available reaction energy is randomly distributed between both hydrogen atoms. Quasiclassical trajectory calculations having the same initial starting conditions as those in the experiment have been carried out using calculated and measured ${\mathrm{H}}_{2}\mathrm{O}$ potential-energy surfaces, together with the knowledge of the various curve crossings, intersections, and estimations of the necessary coupling strengths. The results of these calculations, product state population distributions together with the geometries of the potential surfaces which contribute to the reaction, are compared to those observed in the experiment and allow questions to be answered on the dominance of three-body dissociation.

Rate coefficients and absolute cross sections for center-of-mass energies between 0.0001 and 1 eV are reported for both resonant ion-pair formation and dissociative recombination in electron collisions with HF{sup +} ions. The heavy-ion storage ring CRYRING in Stockholm was used for these measurements. Notable is the fact that the dissociative recombination cross section is substantially smaller than that for most diatomic molecular ions. The recombination seems to have an underlying E{sup -1} energy dependence characteristic of the direct process in dissociative recombination, but both cross sections show structure, which may be attributed to contributions from different indirect processes. The cross sections have no observable energy thresholds. The ratio of the cross section for resonant ion-pair formation to that for dissociative recombination is about 0.25 at 10{sup -3} eV, with the ratio depending on the interaction energy, so the competition of the ion-pair process is much stronger than for other ions so far studied. The HF{sup +} ion is unique in the fact that the electron affinity of F, the binding energy of HF{sup +}, and energy of the atom pair [H(n=2)+F({sup 2}P{sub 3/2})] are the same within the rotational-energy spread of the HF{sup +} target. The resonant ion-pair formation process,more » e+HF{sup +}{yields}H{sup +}+F{sup -}, has some similarities to the photon process, h{nu}+HF{yields}H{sup +}+F{sup -}, and we discuss comparisons. We deduce thermal rate coefficients from our measurements and discuss them in the context of rate coefficients for other diatomic ions available in the literature.« less

Dissociative recombination of vibrationally relaxed H2O+ ions with electrons has been studied in the heavy-ion storage ring CRYRING. Absolute cross-sections have been measured for collision energies between 0 eV and 30 eV. The energy dependence of the cross-section below 0.1 eV is found to be much steeper than the E−1 behaviour associated with the dominance of the direct recombination mechanism. Resonant structures found at 4 eV and 11 eV have been attributed to the electron capture to Rydberg states converging to electronically excited ionic states. Complete branching fractions for all dissociation channels have been measured at a collision energy of 0 eV. The dissociation process is dominated by three-body H + H + O breakup that occurs with a branching ratio of 0.71.

To better understand the propensity for the three-body breakup in dissociative recombination (DR) of dihydrides (H{sub 3}{sup +} , NH{sub 2}{sup +} , CH{sub 2}{sup +} , and H{sub 2}O {sup +} ), we undertook a study of the dynamics of this process. A study of DR of H{sub 2}O {sup +} to give O+H+H was carried out at the CRYRING Heavy-Ion Storage Ring in Stockholm. With the stored beam energy of 4.5MeV, we separated the O signal from the H signals with a differential absorber, thus reducing the problem to a sum of two two-body problems. Results included (1) the ratio of O({sup 3} P) to O({sup 1} D) product, (2) the distribution of recoil-kinetic energy between the two hydrogen atoms, (3) the angular distribution between the hydrogen atoms in the O({sup 3} P) channel and in the O({sup 1} D) channel.

Short review of branching ratios measurements in dissociative recombination process of polyatomic molecules by means of storage ring is given, with the main advantages of this experimental technique.

In the paper we report the first experimental observation of rotational state effects in dissociative recombination of H2+. We also report the branching fractions from the DR of BH2+ N3+ and O3+ and the dynamics occurring in the full fragmentation channel are discussed.

The vibrational population of the hydroxyl radical, OH, formed in the OH+H+H channel arising from the dissociative recombination of the hydronium ion, H(3)O(+), has been investigated at the storage ring CRYRING using a position-sensitive imaging detector. Analysis shows that the OH fragments are predominantly produced in the v=0 and v=1 states with almost equal probabilities. This observation is in disagreement with earlier FALP experiments, which reported OH(v=0) as the dominant product. Possible explanations for this difference are discussed.

Dissociative recombination (DR) of the water cluster ions H(+)(H(2)O)(3) and D(+)(D(2)O)(3) with electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). For the first time, absolute DR cross sections have been measured for H(+)(H(2)O)(3) in the energy range of 0.001-0.8 eV, and relative cross sections have been measured for D(+)(D(2)O)(3) in the energy range of 0.001-1.0 eV. The DR cross sections for H(+)(H(2)O)(3) are larger than previously observed for H(+)(H(2)O)(n) (n=1,2), which is in agreement with the previously observed trend indicating that the DR rate coefficient increases with size of the water cluster ion. Branching ratios have been determined for the dominating product channels. Dissociative recombination of H(+)(H(2)O)(3) mainly results in the formation of 3H(2)O+H (probability of 0.95+/-0.05) and with a possible minor channel resulting in 2H(2)O+OH+H(2) (0.05+/-0.05). The dominating channels for DR of D(+)(D(2)O)(3) are 3D(2)O+D (0.88+/-0.03) and 2D(2)O+OD+D(2) (0.09+/-0.02). The branching ratios are comparable to earlier DR results for H(+)(H(2)O)(2) and D(+)(D(2)O)(2), which gave 2X(2)O+X (X=H,D) with a probability of over 0.9.