Experimental Determination of the Dissociative Recombination Rate Coefficient for Rotationally Cold CH⁺ and Its Implications for Diffuse Cloud Chemistry

Observations of CH+ are used to trace the physical properties of diffuse clouds, but this requires an accurate understanding of the underlying CH+ chemistry. Until this work, the most uncertain reaction in that chemistry was dissociative recombination (DR) of CH+. Using an electron–ion merged-beams experiment at the Cryogenic Storage Ring, we have determined the DR rate coefficient of the CH+ electronic, vibrational, and rotational ground state applicable for different diffuse cloud conditions. Our results reduce the previously unrecognized order-of-magnitude uncertainty in the CH+ DR rate coefficient to ∼20% and are applicable at all temperatures relevant to diffuse clouds, ranging from quiescent gas to gas locally heated by processes such as shocks and turbulence. Based on a simple chemical network, we find that DR can be an important destruction mechanism at temperatures relevant to quiescent gas. As the temperature increases locally, DR can continue to be important up to temperatures of ∼600 K, if there is also a corresponding increase in the electron fraction of the gas. Our new CH+ DR rate-coefficient data will increase the reliability of future studies of diffuse cloud physical properties via CH+ abundance observations

Dose-dependent interleukin-3 stimulation of thrombopoiesis and neutropoiesis in patients with small-cell lung carcinoma before and following chemotherapy: a placebo-controlled randomized phase Ib study.

PURPOSE: To evaluate the safety, tolerance, and hematologic effects of recombinant human interleukin-3 (IL-3) in patients with small-cell lung cancer (SCLC) before and following multiagent antineoplastic therapy in a placebo-controlled, randomized, double-blind study. PATIENTS AND METHODS: Twenty-eight patients (22 men and six women; median age, 60 years) with previously untreated SCLC entered the study. Patients were assigned to six groups of escalating-dose IL-3 ranging from 0.25 to 10 micrograms/kg/d administered by continuous infusion for 7 days, with one patient in each group receiving placebo. After a 1-week interval, the first of three cycles of carboplatin, etoposide (VP16), and epirubicin (CVE) given every 3 weeks was administered. The second cycle of CVE was followed by 7 days of IL-3 administered at the same daily dose as administered during the first infusion. RESULTS: The maximum-tolerated dose was not encountered in this study. Fever was the most frequently observed side effect. Before any chemotherapy, World Health Organization (WHO) grade II fever only appeared at doses > or = 2.5 micrograms/kg/d. Other side effects included rash, headache, and myalgia. During the first infusion of IL-3, before administration of chemotherapy, dose-dependent increases in peripheral-platelet counts (r = .613; P or = 2.5 micrograms/kg of IL-3 (P = .036). Compared with an age-matched historical group receiving identical chemotherapy (n = 191), administration of IL-3 did not modify either disease-free survival or overall patient survival rates. CONCLUSION: IL-3 is well tolerated at doses up to 10 micrograms/kg/d. In the absence of chemotherapy, biologic effects on both neutrophils and platelets were seen at doses > or = 2.5 micrograms/kg/d. IL-3 infusion following the second cycle of CVE appears to reduce chemotherapy-induced myelosuppression, but does not alter tumor response or patient survival rates

Isochronous mass spectrometry in an electrostatic storage ring

For sensitive studies of molecular ions in electrostatic storage rings, the exact knowledge of the isobaric composition of stored beams from a variety of ion sources is essential. Conventional mass-filtering techniques are often inefficient to resolve the beam components. Here, we report the first isochronous mass spectrometry in an electrostatic storage ring, which offers a high mass resolution of Δm/m −5 even for heavy molecular species with m > 100 u and uncooled ion beams. Mass contaminations can be resolved and identified at relative fractions down to 0.02%

Metastable states of Si− observed in a cryogenic storage ring

We have used the Cryogenic Storage Ring (CSR) at the Max Planck Institute for Nuclear Physics to study long-lived metastable states of the silicon anion. A Si- beam of 58 keV kinetic energy was stored in the ultra-high cryogenic vacuum of the CSR, employing only electrostatic deflection elements. We used laser systems at various wavelengths to infer information on the decay of the metastable anionic states by selective photodetachment. Our results give evidence of an excited anionic state for which we determine the extremely long lower lifetime limit of 5.7 h at 90% confidence level, consistent with theoretical predictions for the ^2D term. Furthermore, we find an average lifetime of τ = (22:2 ± 2:5) s for the weakly bound ^2P states, employing coincidence counting with a pulsed nanosecond laser at 2.45 µm. Using a laser depletion technique, we produce a pure ground term ^4S_3/2 Si- beam, and we quantify the fraction of ions in metastable states in our initial ion sample. We combine our experimental efforts with state-of-the-art Multiconfiguration Dirac- Hartree-Fock calculations for the radiative lifetimes of all metastable levels of Si-. We find these calculations to be in excellent agreement with our measurements, and to improve previous efforts considerably

Quantum-state–selective electron recombination studies suggest enhanced abundance of primordial HeH⁺

The epoch of first star formation in the early Universe was dominated by simple atomic and molecular species consisting mainly of two elements: hydrogen and helium. Gaining insight into this constitutive era requires a thorough understanding of molecular reactivity under primordial conditions. We used a cryogenic ion storage ring combined with a merged electron beam to measure state-specific rate coefficients of dissociative recombination, a process by which electrons destroy molecular ions. We found a pronounced decrease of the electron recombination rates for the lowest rotational states of the helium hydride ion (HeH+), compared with previous measurements at room temperature. The reduced destruction of cold HeH+ translates into an enhanced abundance of this primordial molecule at redshifts of first star and galaxy formation