Stability and Cooling of the C_{7}^{2-} Dianion

We have studied the stability of the smallest long-lived all carbon molecular dianion (C_{7}^{2-}) in new time domains and with a single ion at a time using a cryogenic electrostatic ion-beam storage ring. We observe spontaneous electron emission from internally excited dianions on millisecond timescales and monitor the survival of single colder C_{7}^{2-} molecules on much longer timescales. We find that their intrinsic lifetime exceeds several minutes-6 orders of magnitude longer than established from earlier experiments on C_{7}^{2-}. This is consistent with our calculations of vertical electron detachment energies predicting one inherently stable isomer and one isomer which is stable or effectively stable behind a large Coulomb barrier for C_{7}^{2-}→C_{7}^{-}+e^{-} separation.

Erratum: Rotationally Cold OH^{-} Ions in the Cryogenic Electrostatic Ion-Beam Storage Ring DESIREE [Phys. Rev. Lett. 119, 073001 (2017)]

This corrects the article DOI: 10.1103/PhysRevLett.119.073001.

Dianion diagnostics in DESIREE: High-sensitivity detection of Cn2- from a sputter ion source

A sputter ion source with a solid graphite target has been used to produce dianions with a focus on carbon cluster dianions, C_n^2-, with n = 7-24. Singly and doubly charged anions from the source were accelerated together to kinetic energies of 10 keV per atomic unit of charge and injected into one of the cryogenic (13 K) ion-beam storage rings of the Double ElectroStatic Ion Ring Experiment facility at Stockholm University. Spontaneous decay of internally hot C_n^2- dianions injected into the ring yielded C_n^- anions with kinetic energies of 20 keV, which were counted with a microchannel plate detector. Mass spectra produced by scanning the magnetic field of a 90° analyzing magnet on the ion injection line reflect the production of internally hot C₇^2- - C₂₄^2- dianions with lifetimes in the range of tens of microseconds to milliseconds. In spite of the high sensitivity of this method, no conclusive evidence of C₆^2- was found while there was a clear C₇^2- signal with the expected isotopic distribution. This is consistent with earlier experimental studies and with theoretical predictions. An upper limit is deduced for a C₆^2- signal that is two orders-of-magnitude smaller than that for C₇^2-. In addition, C_nO^2- and C_nCu^2- dianions were detected.

Rotationally Cold OH^{-} Ions in the Cryogenic Electrostatic Ion-Beam Storage Ring DESIREE

We apply near-threshold laser photodetachment to characterize the rotational quantum level distribution of OH^{-} ions stored in the cryogenic ion-beam storage ring DESIREE at Stockholm University. We find that the stored ions relax to a rotational temperature of 13.4±0.2  K with 94.9±0.3% of the ions in the rotational ground state. This is consistent with the storage ring temperature of 13.5±0.5  K as measured with eight silicon diodes but in contrast to all earlier studies in cryogenic traps and rings where the rotational temperatures were always much higher than those of the storage devices at their lowest temperatures. Furthermore, we actively modify the rotational distribution through selective photodetachment to produce an OH^{-} beam where 99.1±0.1% of approximately one million stored ions are in the J=0 rotational ground state. We measure the intrinsic lifetime of the J=1 rotational level to be 145±28  s.

Storing keV negative ions for an hour: the lifetime of the metastable ^(2)P((1/2)^(o)) level in ^(32)S^(-)

We use a novel electrostatic ion storage ring to measure the radiative lifetime of the upper level in the 3p^{5} ^{2}P_{1/2}^{o}→3p^{5} ^{2}P_{3/2}^{o} spontaneous radiative decay in ^{32}S^{-} to be 503±54  sec. This is by orders of magnitude the longest lifetime ever measured in a negatively charged ion. Cryogenic cooling of the storage ring gives a residual-gas pressure of a few times 10^{-14} mbar at 13 K and storage of 10 keV sulfur anions for more than an hour. Our experimental results differ by 1.3σ from the only available theoretical prediction [P. Andersson et al., Phys. Rev. A 73, 032705 (2006)].

First storage of ion beams in the Double Electrostatic Ion-Ring Experiment: DESIREE

We report on the first storage of ion beams in the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. We have produced beams of atomic carbon anions and small carbon anion molecules (C(n)(-), n = 1, 2, 3, 4) in a sputter ion source. The ion beams were accelerated to 10 keV kinetic energy and stored in an electrostatic ion storage ring enclosed in a vacuum chamber at 13 K. For 10 keV C2 (-) molecular anions we measure the residual-gas limited beam storage lifetime to be 448 s ± 18 s with two independent detector systems. Using the measured storage lifetimes we estimate that the residual gas pressure is in the 10(-14) mbar range. When high current ion beams are injected, the number of stored particles does not follow a single exponential decay law as would be expected for stored particles lost solely due to electron detachment in collision with the residual-gas. Instead, we observe a faster initial decay rate, which we ascribe to the effect of the space charge of the ion beam on the storage capacity.

The double electrostatic ion ring experiment: a unique cryogenic electrostatic storage ring for merged ion-beams studies

We describe the design of a novel type of storage device currently under construction at Stockholm University, Sweden, using purely electrostatic focussing and deflection elements, in which ion beams of opposite charges are confined under extreme high vacuum cryogenic conditions in separate "rings" and merged over a common straight section. The construction of this double electrostatic ion ring experiment uniquely allows for studies of interactions between cations and anions at low and well-defined internal temperatures and centre-of-mass collision energies down to about 10 K and 10 meV, respectively. Position sensitive multi-hit detector systems have been extensively tested and proven to work in cryogenic environments and these will be used to measure correlations between reaction products in, for example, electron-transfer processes. The technical advantages of using purely electrostatic ion storage devices over magnetic ones are many, but the most relevant are: electrostatic elements which are more compact and easier to construct; remanent fields, hysteresis, and eddy-currents, which are of concern in magnetic devices, are no longer relevant; and electrical fields required to control the orbit of the ions are not only much easier to create and control than the corresponding magnetic fields, they also set no upper mass limit on the ions that can be stored. These technical differences are a boon to new areas of fundamental experimental research, not only in atomic and molecular physics but also in the boundaries of these fields with chemistry and biology. For examples, studies of interactions with internally cold molecular ions will be particular useful for applications in astrophysics, while studies of solvated ionic clusters will be of relevance to aeronomy and biology.

Two-center double-capture interference in fast He2+ + H2 collisions

We report the first observation of Young-type interference effects in a two-electron transfer process. These effects change strongly as the projectile velocity changes in fast (1.2 and 2.0 MeV) He(2+) + H(2) collisions as manifested in strong variations of the double-electron capture rates with the H(2) orientation. This is consistent with fully quantum mechanical calculations, which ignore sequential electron transfer, and a simple projectile de Broglie wave picture assuming that two-electron transfer probabilities are higher in collisions where the projectile passes close to either one of the H(2) nuclei.

Evidence of wave-particle duality for single fast hydrogen atoms

We report the direct observation of interference effects in a Young's double-slit experiment where the interfering waves are two spatially separated components of the de Broglie wave of single 1.3 MeV hydrogen atoms formed close to either target nucleus in H++H2 electron-transfer collisions. Quantum interference strongly influences the results even though the hydrogen atoms have a de Broglie wavelength, lambda_{dB}, as small as 25 fm.

Influence of different phosphorus levels and phytase supplementation in gestation diets on sow performance

A total of 104 sows of different parities were studied. They were fed four diets with different phosphorus (P) levels during gestation for two reproductive cycles, while the same diet was fed during lactation. The aim was to decrease the total P level in the diet during gestation and to evaluate the effect on sow performance. The gestation treatments were low P (LP-; 3.7 g P/kg feed), low P with phytase (LP+, Ronozyme P; 765 FTU/kg feed), medium P (MP; 4.5 g P/kg feed) and high P (HP; 6.0 g P/kg feed). Daily feed allowances were 2.6 kg during gestation and 9.2 kg during lactation. Number of born piglets and piglet mortality were higher (p < 0.05) in the LP treatments than in the MP and HP treatments. No difference (p > 0.05) in the numbers of live-born piglets, piglet birthweights, sow weights or piglet weight gains was found between the treatments. Phosphorus level in sow milk was the highest (p < 0.05) in the MP treatment, while no effects (p > 0.05) of treatment were found on milk Ca levels, P and Ca levels in serum of sows and piglets, nor on the analysed mineral, fat and protein contents of piglets. The estimated average requirement of P for the entire gestation period was 4.4-4.5 g/day. In conclusion, a reduction of dietary total P content during gestation did not result in negative effects on sow or piglet performance. This suggests that it should be possible to lower the dietary P content for gestating sows, compared with earlier recommendations, and thereby reduce the environmental P pollution.

Influence of phosphorus level and soaking of food on phosphorus availability and performance in growing-finishing pigs

The effects of 1-h soaking of a pig diet based on wheat and barley with low (4·1 g P per kg) and high (6·8 g P per kg) total phosphorus (P) content on total tract apparent digestibility and performance in growing-finishing pigs were studied in a balance and a performance trial respectively. Phosphorus bound to inositol penta- and hexaphosphate (IP5-IP6) was reduced by proportionately 0·1 in the soaked food. Soaking numerically increased the apparent digestibility of P. The digestibility of P did not differ between the dry high P and the soaked low P. Excretion of P in urine was correlated (R2= 0·84) with the intake of digestible P. The average daily weight gain, final body weight and carcass weight were lower (P< 0·001), and the energy conversion ratio was higher (P< 0·001) in the dry low P treatment than in the other treatments. Pigs on the low P diets had lower levels of inorganic P in serum (P< 0·01) and slightly higher serum Ca values (P< 0·05) and there were no effects of soaking. The density of femur was lower (P< 0·01) in both the low P treatments than in the high P treatments, and soaking of the low P diet improved (P< 0·01) femur density. In conclusion, a 1-h soaking of pig food in water appears to be sufficient to improve P availability and growth performance.

Dissociative recombination of protonated methanol

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.

Model and observations of Schottky-noise suppression in a cold heavy-ion beam

Some years ago it was found at GSI in Darmstadt that the momentum spread of electron-cooled beams of highly charged ions dropped abruptly to very low values when the particle number decreased to 10 000 or less. This has been interpreted as an ordering of the ions, such that they line up after one another in the ring. We report observations of similar transitions at CRYRING, including an accompanying drop in Schottky-noise power. We also introduce a model of the ordered beam from which the Schottky-noise power can be calculated numerically. The good agreement between the model calculation and the experimental data is seen as evidence for a spatial ordering of the ions.

Hematological and blood chemical data in pigs fed on fine, medium and coarse ground dry grain

Blood was collected the day before slaughter from pigs fed fine, medium or coarse ground grain and examined in accordance with Tables 1–3. Of the 15 pigs (group 1) on the finest meal all except one developed parakeratotic or erosive changes (Figs. 1–5) in the pars oesophagea of the stomach. In group 2 (medium ground) the corresponding number was seven out of 18. No pathological alterations could be detected in the stomach of the pigs on coarse grain.

Statistically significant or almost significant differences were obtained between the groups for hemoglobin, hematocrit, number of erythrocytes, urea-N and pepsinogen. A much wider range was observed in the γ-globulins of the group on fine grain than in the other two groups. The differences in proteins were, however, not significant. To see whether the observed differences between the groups were related to the gastric pathological alterations or to the feed, a comparison was made between pigs with and without pathological changes (Table 3). There were still significant, though smaller, differences in the hemoglobin and hematocrit values. A higher level of significance was only obtained for pepsinogen.