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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...

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 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...

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.

Laser induced fluorescence spectroscopy has been applied for the first time on a stored fast molecular ion beam. The rotational temperature of the N2+ ion beam was studied as a function of storage time. For up to 1 s of storage time, a temperature of 1040 K can be used to describe the rotational energy distribution.

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.