Temperature-Dependent Reaction Kinetics of the Carbanions C and CH ( = 2 and 4) with H Atoms in a Cryogenic Ion Trap.

We report on the temperature-dependent reactions of the carbon-chain anions C and C, as well as the hydrocarbons CH and CH with H atoms in the temperature regime between 8 and 296 K. The experiments have been carried out in a temperature-variable radiofrequency multipole ion trap. From the measured kinetics, we have derived reaction rate coefficients that are constant for all considered systems in the measured temperature regime.

Reaction dynamics of the methoxy anion CHO with methyl iodide CHI.

Studying larger nucleophiles in bimolecular nucleophilic substitution (S2) reactions bridges the gap from simple model systems to those relevant to organic chemistry. Therefore, we investigated the reaction dynamics between the methoxy anion (CHO) and iodomethane (CHI) in our crossed-beam setup combined with velocity map imaging at the four collision energies 0.4, 0.

Imaging the Ion-Molecule Reaction Dynamics of O + CD.

While neutral reactions involved in methane oxidation have been intensively studied, much less information is known about the reaction dynamics of the oxygen radical anion with methane. Here, we study the scattering dynamics of this anion-molecule reaction using crossed-beam velocity map imaging with deuterated methane. Differential scattering cross sections for the deuterium abstraction channel have been determined at relative collision energies between 0.

Vibrational Quenching of Optically Pumped Carbon Dimer Anions.

Careful control of quantum states is a gateway to research in many areas of science such as quantum information, quantum-controlled chemistry, and astrophysical processes. Precise optical control of molecular ions remains a challenge due to the scarcity of suitable level schemes, and direct laser cooling has not yet been achieved for either positive or negative molecular ions. Using a cryogenic wire trap, we show how the internal quantum states of C_{2}^{-} anions can be manipulated using optical pumping and inelastic quenching collisions with H_{2} gas.

Collision-induced state-changing rate coefficients for cyanogen backbones NCN Σ and CNN Σ in astrophysical environments.

We report quantum calculations involving the dynamics of rotational energy-transfer processes, by collision with He atoms in interstellar environments, of the title molecular species which share the presence of the CN backbone and are considered of importance in those environments. The latter structural feature is taken to be especially relevant for prebiotic chemistry and for its possible role in the processing of the heterocyclic rings of RNA and DNA nucleobases in the interstellar space. We carry out calculations of their interaction potentials with He atoms and further obtain the state-to-state rotationally inelastic cross sections and rate coefficients over the relevant range of temperatures.

Investigating Possible Dipole-Bound States of Cyanopolyynes: the Case for the C N Anion Detected in Interstellar Space.

We present results of quantum structure calculations aimed at demonstrating the possible existence of dipole-bound states (DBS) for the anion , a species already detected in the Interstellar medium (ISM). The positive demonstration of DBS existence using ab initio studies is an important step toward elucidating possible pathways for the formation of the more tightly bound valence bound states (VBS) in environments where free electrons from starlight ionization processes are known to be available to interact with the radical partner of the title molecule. Our current calculations show that such excited DBS states can exist in , in agreement with what we had previously found for the smallercyanopolyyne in the series: the anion.

Imaging Frontside and Backside Attack in Radical Ion-Molecule Reactive Scattering.

We report on the reactive scattering of methyl iodide, CHI, with atomic oxygen anions O. This radical ion-molecule reaction can produce different ionic products depending on the angle of attack of the nucleophile O on the target molecule. We present results on the backside and frontside attack of O on CHI, which can lead to I and IO products, respectively.

Dynamics of the Oxygen Atom Transfer Reaction between Carbon Dioxide and the Tantalum Cation.

The understanding of fundamental atomic-level processes often requires well-defined model systems. The oxygen atom transfer from CO to a transition metal cation in the gas phase presents such a model system. We investigate the reaction of Ta + CO for which the formation of TaO is highly efficient and attributed to multistate reactivity.

Three-Body Collisions Driving the Ion-Molecule Reaction C + H at Low Temperatures.

We report on the three-body reaction rate of C with H producing CH studied in a cryogenic 16-pole radio frequency ion trap. The reaction was measured in the temperature range from 10 to 28 K, where it was found to only take place via three-body collisions. The experimentally determined termolecular rate coefficient follows the form of with = 20 K, where = 8.

Vibrational Predissociation Spectra of C N and C N : Bending and Stretching Vibrations.

We present infrared predissociation spectra of C N (H ) and C  N (H ) in the 300-1850 cm range. Measurements were performed using the FELion cryogenic ion trap end user station at the Free Electron Lasers for Infrared eXperiments (FELIX) laboratory. For C N (H ), we detected the CCN bending and CC-N stretching vibrations.

Tunnelling measured in a very slow ion-molecule reaction.

Quantum tunnelling reactions play an important role in chemistry when classical pathways are energetically forbidden, be it in gas-phase reactions, surface diffusion or liquid-phase chemistry. In general, such tunnelling reactions are challenging to calculate theoretically, given the high dimensionality of the quantum dynamics, and also very difficult to identify experimentally. Hydrogenic systems, however, allow for accurate first-principles calculations.

Quasi-classical trajectory study of the OH + CHI reaction: theory meets experiment.

Regarding OH + CHI, several studies have focused on the dynamics of the reaction. Here, high-level quasi-classical trajectory simulations are carried out at four different collision energies on our recently developed potential energy surface. In all, more than half a million trajectories are performed, and for the first time, the detailed quasi-classical trajectory results are compared with the reanalysed crossed-beam ion imaging experiments.

The CHΣ Anion: Inelastic Rate Coefficients from Collisions with He at Interstellar Conditions.

We present accurate calculations on several properties of a gas-phase system of interest in the interstellar medium (ISM), where the title molecular anion has been often surmised but not yet confirmed by observations. The CHΣ constitutes the smallest term in the series of longer anionic polyynes which have been observed in the ISM (e.g.

Imaging the Atomistic Dynamics of Single Proton Transfer and Combined Hydrogen/Proton Transfer in the O + CHI Reaction.

We report on reactive scattering studies of the proton transfer and combined hydrogen/proton transfer in the O + CHI reaction. We combine state-of-the-art crossed-beam velocity map imaging and quantum chemistry calculations to understand the dynamics for the formations of the CHI + OH and CHI + HO products. The experimental velocity- and angle-differential cross section show for both products and at all collision energies (between 0.

Quantum state-dependent anion-neutral detachment processes.

The detachment loss dynamics between rubidium atoms (Rb) and oxygen anions (O) are studied in a hybrid atom-ion trap. The amount of excited rubidium present in the atomic ensemble is actively controlled, providing a tool to tune the electronic quantum state of the system and, thus, the anion-neutral interaction dynamics. For a ground state Rb interacting with O, the detachment induced loss rate is consistent with zero, while the excited state Rb yields a significantly higher loss rate.

Associative detachment in anion-atom reactions involving a dipole-bound electron.

Associative electronic detachment (AED) between anions and neutral atoms leads to the detachment of the anion's electron resulting in the formation of a neutral molecule. It plays a key role in chemical reaction networks, like the interstellar medium, the Earth's ionosphere and biochemical processes. Here, a class of AED involving a closed-shell anion (OH) and alkali atoms (rubidium) is investigated by precisely controlling the fraction of electronically excited rubidium.

Strong ortho/para effects in the vibrational spectrum of Cl(H).

The predissociation spectrum of the Cl-35(H) complex is measured between 450 and 800 cm in a multipole radiofrequency ion trap at different temperatures using the FELIX infrared free electron laser. Above a certain temperature, the removal of the Cl(p-H) para nuclear spin isomer by ligand exchange to the Cl(o-H) ortho isomer is suppressed effectively, thereby making it possible to detect the spectrum of this more weakly bound complex. At trap temperatures of 30.

Complex Formation in Three-Body Reactions of Cl with H.

Three-body reaction rates of Cl with H to form the weakly bound complex Cl(H) are measured between 10 and 26 K in a linear radio-frequency wire trap. Formation of larger clusters of the form Cl(H) are also observed. The three-body (or termolecular) rate coefficients follow the form , with = 1.

Atomistic dynamics of elimination and nucleophilic substitution disentangled for the F + CHCHCl reaction.

Chemical reaction dynamics are studied to monitor and understand the concerted motion of several atoms while they rearrange from reactants to products. When the number of atoms involved increases, the number of pathways, transition states and product channels also increases and rapidly presents a challenge to experiment and theory. Here we disentangle the dynamics of the competition between bimolecular nucleophilic substitution (S2) and base-induced elimination (E2) in the polyatomic reaction F + CHCHCl.

Influence of a Supercritical Electric Dipole Moment on the Photodetachment of C_{3}N^{-}.

Threshold photodetachment spectroscopy of the molecular ion C_{3}N^{-} has been performed at both 16(1) and 295(2) K in a 22-pole ion trap. The 295(2) K spectrum shows a large increase in the cross section with an onset about 200  cm^{-1} below threshold, which is explained by significant vibrational excitation of the trapped ions at room temperature. This excitation disappears at cryogenic temperatures leading to an almost steplike onset of the cross section at threshold, which cannot be adequately described with a Wigner threshold law.