The fundamental rotational transition J = 1←0 of the anion OH(-) has been measured by cooling mass-selected OH(-) ions to 10 K in a 22-pole ion trap and applying a novel rotational-rovibrational two-photon scheme. A transition frequency of (1 123 101.0410 ± 0.0014) MHz was obtained with so far unprecedented accuracy. The general application of the presented action-spectroscopy scheme to other anions and cations is discussed.
Complexes of the triatomic hydrogen ion with helium were synthesised in a low-temperature 22-pole rf ion trap at He number densities of up to 10 16 cm −3 . Absolute ternary rate coefficients for sequentially attaching He atoms have been determined from the growth of complexes with increasing storage time. The number of helium-tagged ions is significantly reduced when increasing the nominal temperature from 4 to 25 K. Competition between attachment and dissociation via collisions leads to stationary He n -H + 3 (n up to 9) distributions. State-specific excitation of the trapped H + 3 ions via IR transitions significantly reduces the formation of complexes. Tuning the laser to v 2 = 1 transitions in the range of 2726 cm −1 leads to LIICG lines, i.e., to spectra caused by laser-induced inhibition of complex growth. In addition, almost 100 lines have been found between 2700 and 2765 cm −1 , which are attributed to laser-induced dissociation of the in situ formed He-H + 3 complex ions. These lines are not yet assigned; however, their absorption strength, statistics and predissociation lifetimes provide interesting information on both the stable complexes as well as on scattering resonances in low-energy H + 3 + He collisions. New calculations of the potential energy surface will help to analyse the dissociation spectrum. There are some indications that para-H + 3 is enriched under the conditions of the present experiment.
IntroductionStudies of reactions between ions and neutrals under conditions relevant for astrochemistry are important for understanding different processes in the interstellar medium (ISM). Reactions involving helium and hydrogen significantly influence the overall evolution of our universe including the early universe chemistry and especially the 'Dark Age'. For modelling such environments, one needs reliable rate coefficients. A detailed discussion of primordial chemistry can be found in [1] and references therein. According to [2], helium became neutral at a red shift of z ∼ 2500. At those times, the density was already very low and the only way to form molecules was via radiative association. Because hydrogen was still ionised, models predict that the first molecule formed in space was HeH + . The coexistence of He and He + also lead to the formation of some He + 2 . Molecules were needed as coolants during the formation of the first galaxies. Also after these early times, helium and hydrogen play an important role. In all models of interstellar ion chemistry, the first steps are ionisation of He and H 2 by cosmic rays.
We
report the first gas-phase vibrational spectra of the hydrocarbon
ions C3H+ and C3H2+. The ions were produced by electron impact ionization of
allene. Vibrational spectra of the mass-selected ions tagged with
Ne were recorded using infrared predissociation spectroscopy in a
cryogenic ion trap instrument using the intense and widely tunable
radiation of a free electron laser. Comparison of high-level quantum
chemical calculations and resonant depletion measurements revealed
that the C3H+ ion is exclusively formed in its
most stable linear isomeric form, whereas two isomers were observed
for C3H2+. Bands of the energetically
favored cyclic c-C3H2+ are in excellent
agreement with calculated anharmonic frequencies, whereas for the
linear open-shell HCCCH+ (2Πg) a detailed theoretical description of the spectrum remains challenging
because of Renner–Teller and spin–orbit interactions.
Good agreement between theory and experiment, however, is observed
for the frequencies of the stretching modes for which an anharmonic
treatment was possible. In the case of linear l-C3H+, small but non-negligible effects of the attached Ne on the
ion fundamental band positions and the overall spectrum were found.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.