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Nitrile ions are abundant in Titan's upper atmosphere and are expected to be lost mainly via dissociative recombination with free electrons. We review in this paper a series of experimental results ...

We have investigated the dissociative recombination (DR) of the C 6 D 6 + and C 6 D 7 + ions using the CRYRING heavy-ion storage ring at Stockholm University, Sweden. The dissociative recombination branching ratios were determined at minimal collision energy, showing that the DR of both ions was dominated by pathways keeping the carbon atoms together in one product. The absolute reaction cross sections for the titular ions are best fitted by σ (E cm [eV]) = 1.3 ± 0.4 × 10 -15 (E cm [eV]) −1.19 ± 0.02 cm 2 (C 6 D 6 + ) and σ (E cm [eV]) = 1.1 ± 0.3 × 10 -15 (E cm [eV]) −1.33 ± 0.02 cm 2 (C 6 D 7 + ) in the intervals 3-300 meV and 3-200 meV respectively. The thermal rate constants of the titular reactions are best described by: k(T) = 1.3 ± 0.4 × 10 -6 (T/300) −0.69 ± 0.02 cm 3 s -1 for C 6 D 6 + and k(T) = 2.0 ± 0.6 × 10 -6 (T/300) −0.83 ± 0.02 cm 3 s -1 for C 6 D 7 + . These expressions correlates well with earlier flowing afterglow studies on the same process.

The dissociative recombination of protonated propionitrile, CH3CH2CNH+, has been investigated at the heavy ion storage ring, CRYRING, at the Manne Siegbahn Laboratory, Stockholm University, Sweden. ...

At the heavy ion storage ring CRYRING in Stockholm, Sweden, we have investigated the dissociative recombination of DCOOD2+ at low relative kinetic energies, from ~1 meV to 1 eV. The thermal rate coefficient has been found to follow the expression k(T) = 8.43 × 10-7 (T/300)^-0.78 cm3 s-1 for electron temperatures, T, ranging from ~10 to ~1000 K. The branching fractions of the reaction have been studied at ~2 meV relative kinetic energy. It has been found that ~87% of the reactions involve breaking a bond between heavy atoms. In only 13% of the reactions do the heavy atoms remain in the same product fragment. This puts limits on the gas-phase production of formic acid, observed in both molecular clouds and cometary comae. Using the experimental results in chemical models of the dark cloud, TMC-1, and using the latest release of the UMIST Database for Astrochemistry improves the agreement with observations for the abundance of formic acid. Our results also strengthen the assumption that formic acid is a component of cometary ices.

In this paper we report the results of a study on the dissociative recombination (DR) of the diacetylene cation, C4D2+, which has been carried out at the ion storage ring CRYRING in Stockholm, Sweden. The energy-dependent absolute DR cross-section as well as the branching fractions at ∼0 eV collision energy were measured. The DR cross-section was best fitted using the expression σ(E) = (7.5 ± 1.5) × 10−16 × E−(1.29±0.03) cm2 over the collision energy range 1–100 meV. The thermal rate coefficient was deduced from the cross-section to be α(T) = (1.10 ± 0.15) × 10−6 × (T/300)−(0.79±0.03) cm3/s. The reported branching fractions for C4D2+ agree with previous experiments on the DR of C4H2+ performed at the ASTRID storage ring in Aarhus, Denmark, and furthermore, indicate that the DR of C4D2+ possesses only two channels leading to the following products: C4D + D (75%) and C2D + C2D (25%).

(2007). Experimental determination of dissociative recombination reaction pathways and absolute reaction cross-sections of CH2OH + , CD2OD + and CD2. Molecular Physics: Vol. 105, A Special Issue In Honour of John M. Brown, pp. 899-906.

The branching ratios of the different reaction pathways and the overall rate coefficients of the dissociative recombination reactions of CH3OH2+ and CD3OD2+ have been measured at the CRYRING storage ring located in Stockholm, Sweden. Analysis of the data yielded the result that formation of methanol or deuterated methanol accounted for only 3 and 6% of the total rate in CH3OH2+ and CD3OD2+, respectively. Dissociative recombination of both isotopomeres mainly involves fragmentation of the C-O bond, the major process being the three-body break-up forming CH3, OH and H (CD3, OD and D). The overall cross sections are best fitted by sigma = 1.2 +/- 0.1 x 10(-15) E(-1.15 +/- 0.02) cm2 and sigma = 9.6 +/- 0.9 x 10(-16) E(-1.20 +/- 0.02) cm2 for CH3OH2+ and CD3OD2+, respectively. From these values thermal reaction rate coefficients of k(T) = 8.9 +/- 0.9 x 10(-7) (T/300)(-0.59 +/- 0.02) cm3 s(-1) (CH3OH2+) and k(T) = 9.1 +/- 0.9 x 10(-7) (T/300)(-0.63 +/- 0.02) cm3 s(-1) (CD3OD2+) can be calculated. A non-negligible formation of interstellar methanol by the previously proposed mechanism via radiative association of CH3+ and H2O and subsequent dissociative recombination of the resulting CH3OH2+ ion to yield methanol and hydrogen atoms is therefore very unlikely.

The paper reports an investigation of the dissociative recombination of at the heavy-ion storage ring CRYRING. The absolute cross-section has been measured as a function of centre-of-mass energy ...

Branching ratios and absolute cross sections have been measured for the dissociative recombination of HCS+ and OCS+ at the CRYRING ion storage ring. In the case of OCS+, the channel leading to CO + S (83%) dominates, whereas the other exoergic pathways leading to CS + O (14%) and C + SO (3%) are of lesser importance. In the case of HCS+, fracture of the C–S bond is predominant (81%), with the production of H + CS accounting for the remainder (19%). The cross section of the reaction could be fitted by the expressions σ = 1.41 × 10-15E(eV)-1.11 and 4.47 × 10-16E(eV)-1.14 cm2 for HCS+ and OCS+, respectively. The derived energy dependences of the thermal reaction rate coefficients can be fitted by k(T) = 9.7 × 10-7(T/300)-0.57 and 3.5 × 10-7(T/300)-0.62 cm3 s-1 for HCS+ and OCS+, respectively. We use these data to perform model calculations on the HCS+/CS abundance ratio in dark clouds and find that the models using the UMIST and Ohio State University databases have even more difficulty in accounting for the large observed ratio.

Branching ratios and absolute cross sections have been measured for the dissociative recombination of DCCCN+ and DCCCND+ using the CRYRING ion storage ring. In the case of DCCCN+ the dissociation y ...

Branching ratios and absolute cross sections have been measured for the dissociative recombination of C3H4+ using the CRYRING ion storage ring. The pre-eminent channel involves the production of C3 ...

Branching ratios and absolute cross sections have been measured for the dissociative recombination of (SO2+)-O-18 using the CRYRING ion storage ring. The branching ratio of the (SO2+)-O-18 + e(-)-->(SO)-O-18+O-18 channel amounts to 61%, while the three-body breakup (SO2+)-O-18 + e(-)-->S+2(18)O accounts for the remaining 39% of the total reaction. The cross section of the reaction could be fitted by the expression sigma=(1.2+/-0.4)x10(-15) E-0.96+/-0.02 cm(2), which leads to a thermal reaction rate of k(T)=(4.6+/-0.2)x10(-7)(T/300 K)(-0.52+/-0.02) cm(3) mol(-1) s(-1).

Branching ratios and absolute cross sections have been measured for the dissociative recombination of N2H+ using the CRYRING ion storage ring. It has been found that the channel N2H+ + e- → N2 + H accounts for only 36% of the total reaction and that the branching into the other exoergic pathway, N2H+ + e- → NH + N, consequently amounts to 64%. The cross section of the reaction could be fitted by the expression σ = (2.4 ± 0.4) × 10-16E-1.04±0.02 cm2, which leads to a thermal reaction rate of k(T) = (1.0 ± 0.2) × 10-7(T/300)-0.51±0.02 cm3 s-1, in favorable agreement with previous flowing afterglow Langmuir probe measurements at room temperature, although our temperature dependence is very different. The implications of these measurements for the chemistry of interstellar clouds are discussed. A standard model calculation for a dark cloud predicts a slight increase of N2H+ in the dark clouds but a five- to sevenfold increase of the NH concentration as steady state is reached.

Branching ratios and absolute cross sections have been measured for the dissociative recombination of N2OD+ using the CRYRING ion storage ring. The most dominating pathways were found to be those leading to N2+OD (46%) and the three-body break-up producing N2+O+D (40%). The production of N2O is not observed. The cross section of the reaction could be fitted to the expression σ=1.25±0.25×10−15(E/eV)−1.24±0.02, which leads to a thermal reaction rate of k(T)=1.4±0.1×10−6(T/300)−0.74±0.02 cm3 s−1. The findings are compared with those of the related dissociative recombination of DOCO+ as well as with earlier flowing afterglow measurements.

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.

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...

The electron cooler at CRYRING is now operating with a superconducting gun solenoid and an electron beam that is adiabatically expanded with a factor of up to 100. This paper describes the new gun solenoid and electron gun. It presents measurements made on longitudinal cooling forces with different expansion factors, electron densities, magnetic field strengths and beam alignments. It also presents studies of a transverse beam instability that appears when a misalignment is introduced between ion and electron beams. Finally, some measurements of dielectronic recombination that directly yield transverse and longitudinal electron temperatures are discussed.

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.

Branching ratios in dissociative recombination of C2H2+ molecular ions with electrons were measured using the CRYRING heavy-ion storage ring. We have determined complete branching ratios for C2H2+ at collision energies between 0 and 7.4 meV. We found dissociative recombination of C2H2+ to be dominated by the two-body C2H+H and three-body C2+H+H channels, with branching ratios of 0.50±0.06 and 0.30±0.05, respectively. The branching to CH+CH was measured to be 0.13±0.01, whereas two other energetically allowed channels were found to be almost negligible.

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 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.

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.

Asymptotic atomic-state branching ratios for the dissociative recombination of both {sup 3}HeD{sup +} and {sup 4}HeH{sup +} have been studied using the CRYRING and TSR heavy-ion storage rings. The kinetic-energy release in the recombination process was measured for incident electron energies between 0 and 15 eV. It was found that the He(1{ital s}{sup 2})+D,H({ital n}=2) channel completely dominates at zero electron energy. The branching ratios observed slightly above the threshold for the {ital n}=3 state of the H (D) atom indicate a rapid switchover of the final-state population to this level. At collision energies above 10 eV many channels leading to excited He atoms are found to contribute, and also a strong angular anisotropy of the dissociation products is observed. {copyright} {ital 1996 The American Physical Society.}

Absolute cross sections for dissociative recombination of HD+ were measured in the ion storage CRYRING for incident electron energies in the range 0.01-20 eV. The ions were stored for about 25 s before data taking, which is several orders of magnitude longer than their vibrational lifetimes towards spontaneous emission of infrared radiation. A broad resonance in the cross section at 5-12 eV is due to recombination into a manifold of doubly excited states. Multichannel quantum-defect theory was used to calculate the absolute cross section of this resonance. The calculations required inclusion of different mechanisms, such as dissociative autoionization, and many molecular states in order to reproduce the resonance region. Very good agreement of experiment and theory is found, and the results strongly reinforce that vibrationally cold ions were used in the experiment.

We have used the CRYRING heavy-ion storage ring at the Manne Siegbahn Laboratory in Stockholm to store and cool beams of ${\mathrm{H}}_{2}$${\mathrm{D}}^{+}$. These beams circulate with energies of MeV per amu and are merged with an electron beam traveling at nearly the same velocity. In this way, relative energies from a fraction of a meV to tens of an eV are achieved. When dissociative recombination (DR) takes place, the neutral fragments exit the ring and strike a detector, enabling the measurement of total DR cross sections. Using this technique, coupled with a ``translucent barrier'' in which some particles pass directly through holes and others pass through a thin solid and lose part of their energy before striking the detector, we are able to measure the total cross section for DR in ${\mathrm{H}}_{3}^{+}$ and the branching into the three-body (H+H+H) channel and the two-body (${\mathrm{H}}_{2}$+H) channel. Coupling this method with the use of energy absorbers, we are able to measure these quantities for ${\mathrm{H}}_{2}$${\mathrm{D}}^{+}$ and the separate two-body channels HD+H and ${\mathrm{H}}_{2}$+D. An isotope effect is observed favoring the formation of HD.

We report the first high-resolution cross section measurements of dissociative recombination in $^{3}\mathrm{He}$${\mathrm{H}}^{+}$ for $0.05 \mathrm{meV}\ensuremath{\le}{E}_{\mathrm{rel}}\ensuremath{\le}300 \mathrm{meV}$. We used the electron cooling beam of the storage ring CRYRING, which now features $k{T}_{\ensuremath{\perp}}\ensuremath{\sim}10$ meV. The experiment confirms the puzzlingly large lowenergy rate measured previously and finds six heretofore unreported peaks at 34, 54, 113, 216, 250, and 284 meV. We remark on the utility of the Fourier transform to remove peak shifts and broadening due to the electron beam's thermal energy spread.

The efficiency of electron cooling can be improved by adiabatically expanding the electron beam in a decreasing magnetic field, thereby lowering the transverse electron temperature. An electron beam expanded by a factor of 10 has been implemented at the CRYRING electron cooler, decreasing the transverse electron temperature from 100 to 10 meV. This has resulted in an increased drag force between ions and electrons and in large reductions of cooling times. Also, the energy resolution in electron-ion recombination experiments at low relative energy has increased by a factor of 10.

CRYRING is a small synchrotron and storage ring equipped with electron cooling. Highly charged ions from the electron beam ion source CRYSIS or singly charged ions from the plasmatron source MINIS are injected via an RFQ into the ring. The facility is in the commissioning phase. Full design energy has been achieved and electron cooling demonstrated both for atomic and molecular ions. The experimental program started in August with two projects, dissociative recombination of H+3 ions and radiative recombination to deuterons. The status as of September 20, 1992, is reported.

We have investigated the dissociative recombination of the N2O+ ion using the CRYRING heavy-ion storage ring at the Manne Siegbahn laboratory in Stockholm, Sweden. The dissociative recombination branching ratios were determined at minimal (approximately 0 eV) collision energy, showing that the dominating pathways involved two-body fragmentation: N2 + O (48%) and NO + N (36%). The branching ratio of the three-body break-up 2N + O was 16%. The overall thermal rate coefficient of the title reaction follows the expression k(T) = 3.34 +/- 0.75 x 10(-7) (T/300) (-0.57+/- 0.03 cm3 s(-1)), which correlates perfectly with earlier flowing afterglow studies on the same process.

International audience; Cross sections and branching ratios are presented for the dissociative recombination of the CF+2 and CF+3 ions with electrons. It is found that the channel producing CF + F is dominant for the reaction with CF+2 and the production of CF2 + F is dominant for the reaction with CF+3. The cross sections for these two ions are very similar.

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 of the development of the CRYRING facility has been aimed at the production, handling and measurement of weak beams, often of ions that are difficult to produce in the ion sources. Due to the diverse requirements for ions, several different ion source types are in use. To be able to handle and measure the weak beams, the beam diagnostic systems have been improved. The ECR source is in regular use for single pass experiments and will be used for experiments in the storage ring before the summer of 2003. The EBIS source has been renovated and upgraded with a new electron gun and will be back in operation in May 2003.

Dimethyl disulfide (DMDS) and N-methylacetamide are two first choice model systems that represent the disulfide bridge bonding and the peptide bonding in proteins. These molecules are therefore suitable for investigation of the mechanisms involved when proteins fragment under electron capture dissociation (ECD). The dissociative recombination cross sections for both protonated DMDS and protonated N-methylacetamide were determined at electron energies ranging from 0.001 to 0.3 eV. Also, the branching ratios at 0 eV center-of-mass collision energy were determined. The present results give support for the indirect mechanism of ECD, where free hydrogen atoms produced in the initial fragmentation step induce further decomposition. We suggest that both indirect and direct dissociations play a role in ECD.

Experimental data are presented from three different heavy-ion storage rings (ASTRID in Aarhus, CRYRING in Stockholm, and TSR in Heidelberg) to assess the reliability of this experimental tool for the extraction of absolute rate coefficients and cross sections for dissociative recombination (DR). The DR reaction between HD. and electrons has been studied between 0 and 30 eV on a dense energy grid. HD+ displays two characteristic local maxima in the DR rate around 9 and 16 eV. These maxima influence the data analysis at smaller collision energies. We conclude that resonant structures in the DR cross sections are reproduced among the experiments within the collision energy resolution. The absolute cross sections agree within the systematic experimental errors of 20% related to the measurement of the ion currents. Absolute thermal rate coefficients for HD. ions are given for an electron temperature range of 50-300 K. Results for the DR cross section and the thermal rate coefficients are compared to recent theoretical calculations including rotational effects, finding satisfactory agreement.

Knowledge of the abundance of H(3)(+) is needed in interstellar and planetary atmospheric chemistry. An important destruction mechanism of H(3)(+) is low-energy electron impact followed by dissociation, but estimates of the reaction rate span several orders of magnitude. As an attempt to resolve this uncertainty, the cross section for dissociative recombination of vibrationally cold H(3)(+) has been measured with an ion storage ring down to collision energies below 1 millielectron volt. A rate coefficient of 1.15 x 10(-7) cubic centimeters per second at 300 kelvin was deduced. The cross section scaled with collision energy according to E(-1.15), giving thee rate a temperature dependence of T(-0.65).

The experimental program at CRYRING storage ring began shortly after the installation of the electron cooler in May 1992. The performance of the ion sources and the ring is reported. Results of electron cooling are reviewed and a method to improve the efficiency of electron cooling is presented. >

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

Resonant ion-pair formation from the collisions of ${\mathrm{NO}}^{+}$ ions with electrons was studied using the heavy-ion storage ring CRYRING at the Manne Siegbahn Laboratory of Stockholm University. The total cross section is measured for the formation of ${\mathrm{N}}^{+}{+\mathrm{O}}^{\mathrm{\ensuremath{-}}}$ for electron energies 8--18 eV, and the results are compared with ion-pair formation in photoionization work. A peak in the cross section is observed at 12.5 eV, with a magnitude of $8.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19}{\mathrm{cm}}^{2}.$ An attempt to extract the cross section for the reverse process of associative ionization is made.

Resonant ion-pair formation from collisions of electrons with electronic and vibronic ground-state diatomic molecular ions has been studied in the present work for ${\mathrm{HD}}^{+}$ and ${\mathrm{OH}}^{+}.$ The cross section for ${\mathrm{HD}}^{+}$ has a magnitude of the order of $3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}19} {\mathrm{cm}}^{2}$ and is characterized by an energy threshold and 14 resolved peaks in the energy range up to 16 eV. A theoretical study confirms that the structures derive primarily from quantum interference of the multiple dissociation pathways. Measurements for ${\mathrm{OH}}^{+}$ reveal that the cross section for ${\mathrm{H}}^{+}$ and ${\mathrm{O}}^{\ensuremath{-}}$ formation is lower than ${10}^{\ensuremath{-}21} {\mathrm{cm}}^{2}$ at energies of 6 and 12 eV.

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.

The rapid development of the accelerator technology which enables the construction of reliable and very intense neutron sources has initiated a growing interest for acceleratordriven transmutation systems in Sweden. After the Specialist Meeting on Accelerator‐Driven Transmutation Technology for Radwaste and other Applications on 24–28 June 1991 at Saltsjobaden, Sweden the research activities oriented towards accelerator‐driven systems have been started at several research centers in Sweden. Also the governmental agencies responsible for the spent fuel policy showed a positive attitude to these activities through a limited financial support, particularly for studies of the safety aspects of these systems. Also the nuclear power industry and utilities show a positive interest in the research on these concepts. The present paper presents an overview of the Swedish research activities on accelerator‐driven systems and the proposed future coordination, organizations and prospects for this research in the context of the national nuclear energy and spent fuel policy. The Swedish perspective for international cooperation is also described.

CH3+ is an important molecular ion in the astrochemistry of diffuse clouds, dense clouds, cometary comae, and planetary ionospheres. However, the rate of one of the major destruction mechanisms of CH3+, dissociative recombination (DR), has long been uncertain, hindering the use of CH3+ as an astrochemical probe. Here, we present the first absolute measurement of the DR of vibrationally cold CH3+, which has been made using the heavy storage ring CRYRING in Stockholm, Sweden. From our collision-energy-dependent cross sections, we infer a thermal rate constant of k(T) = 6.97(+/- 0.03) x 10(-7)(T/300)(-0.61(+/- 0.01)) cm(3) s(-1) over the region 10 K AuthorCount:12

The dissociative recombination (DR) of N2H+ has been reinvestigated at the heavy ion storage ring CRYRING at the Manne Siegbahn Laboratory in Stockholm, Sweden. Thermal rate coefficients for electr ...

Ion storage rings offer several advantages for studies of recombination of molecular ions by electrons, a process which in general leads to dissociation. During the last year dissociative recombination of H+3, HD+, H+2, 3HeH+, 4HeH+, and 4HeD+ have been studied in storage rings in Stockholm, Heidelberg, Tokyo, and Aarhus. Only a fraction of the results obtained at these places have been processed to the point where they have been published in the literature. Hence, the discussion of some of the results in this article must be regarded as tentative.

Aims. We determine branching fractions, cross sections and thermal rate constants for the dissociative recombination of CD3CDOD + and CH3CH2OH + at the low relative kinetic energies encountered in the interstellar medium. Methods. The experiments were carried out by merging an ion and electron beam at the heavy ion storage ring CRYRING, Stockholm, Sweden. Results. Break-up of the CCO structure into three heavy fragments is not found for either of the ions. Instead the CCO structure is retained in 23 ± 3% of the DR reactions of CD3CDOD + and 7 ± 3% in the DR of CH3CH2OH + , whereas rupture into two heavy fragments occurs in 77 ± 3% and 93 ± 3% of the DR events of the respective ions. The measured cross sections were fitted between 1–200 meV yielding the following thermal rate constants and cross-section dependencies on the relative kinetic energy: σ(Ecm[eV]) = 1.7 ± 0.3 × 10 −15 (Ecm[eV]) −1.23±0.02 cm 2 and k(T) = 1.9 ± 0.4 × 10 −6 (T/300) −0.73±0.02 cm 3 s −1 for CH3CH2OH + as well as k(T) = 1.1 ± 0.4 × 10 −6 (T/300) −0.74±0.05 cm 3 s −1 and σ(Ecm[eV]) = 9.2 ± 4 × 10 −16 (Ecm[eV]) −1.24±0.05 cm 2 for CD3CDOD +

Aims: Determination of branching fractions, cross sections and thermal rate coefficients for the dissociative recombination of CD3OCD2+ (0-0.3 eV) and (CD3)2OD+ (0-0.2 eV) at the low relative kinet ...

Dissociative recombination (DR) of water cluster ions H(+)(H(2)O)(n) (n=4-6) with free electrons has been studied at the heavy-ion storage ring CRYRING (Manne Siegbahn Laboratory, Stockholm University). For the first time, branching ratios have been determined for the dominating product channels and absolute DR cross sections have been measured in the energy range from 0.001 to 0.7 eV. Dissociative recombination is concluded to result in extensive fragmentation for all three cluster ions, and a maximum number of heavy oxygen-containing fragments is produced with a probability close to unity. The branching ratio results agree with earlier DR studies of smaller water cluster ions where the channel nH(2)O+H has been observed to dominate and where energy transfer to internal degrees of freedom has been concluded to be highly efficient. The absolute DR cross sections for H(+)(H(2)O)(n) (n=4-6) decrease monotonically with increasing energy with an energy dependence close to E(-1) in the lower part of the energy range and a faster falloff at higher energies, in agreement with the behavior of other studied heavy ions. The cross section data have been used to calculate DR rate coefficients in the temperature range of 10-2000 K. The results from storage ring experiments with water cluster ions are concluded to partly confirm the earlier results from afterglow experiments. The DR rate coefficients for H(+)(H(2)O)(n) (n=1-6) are in general somewhat lower than reported from afterglow experiments. The rate coefficient tends to increase with increasing cluster size, but not in the monotonic way that has been reported from afterglow experiments. The needs for further experimental studies and for theoretical models that can be used to predict the DR rate of polyatomic ions are discussed.