Experimental Characterization of the Isomer-Selective Generation of the Astrochemically Relevant Hydroxymethylene Radical Cation (HCOH/DCOH).

Interest in the observation and characterization of organic isomers in astronomical environments has grown rapidly with an increase in the sensitivity of detection techniques. Accurate modeling and interpretation of these environments require experimental isomer-specific reactivity and spectroscopic measurements. Given the abundance of formaldehyde (HCO) in various astrophysical objects, the properties and reactivities of its cation isomers HCO and HCOH are of significant interest.

Combined experimental and computational study of the reactivity of the methanimine radical cation (HCNH˙) and its isomer aminomethylene (HCNH˙) with propene (CHCHCH).

The gas phase reactivity of the radical cation isomers HCNH˙ (methanimine) and HCNH˙ (aminomethylene) with propene (CHCHCH) has been investigated by measuring absolute reactive cross sections and product branching ratios, under single collision conditions, as a function of collision energy (in the range ∼0.07-11.80 eV) using guided ion beam mass spectrometry coupled with VUV photoionization for selective isomer generation.

The role of intersystem crossing in the reactive collision of S+(4S) with H2.

We report a study on the reactive collision of S+(4S) with H2, HD, and D2 combining guided ion beam experiments and quantum-mechanical calculations. It is found that the reactive cross sections reflect the existence of two different mechanisms, one being spin-forbidden. Using different models, we demonstrate that the spin-forbidden pathway follows a complex mechanism involving three electronic states instead of two as previously thought.

An innovative method to identify structural change through ion-molecule collision, making use of Time-Of-Flight measurements and SIMION simulations.

Structural change of ions induced by collision with a neutral has been studied in a guided ion beam tandem mass spectrometer, using Time-Of-Flight measurements and SIMION simulation. The exothermic catalytic isomerization of HOC to HCO is used to explore the new methodology. Isomerization is catalyzed via a proton transport mechanism through the interplay of a neutral molecule, the catalyst.

Reactivity of the Ethenium Cation (CH) with Ethyne (CH): A Combined Experimental and Theoretical Study.

The gas-phase reaction between the ethyl cation (CH) and ethyne (CH) is re-investigated by measuring absolute reactive cross sections (CSs) and branching ratios (BRs) as a function of collision energy, in the thermal and hyperthermal energy range, via tandem-guided ion beam mass spectrometry under single collision conditions. Dissociative photoionization of CHBr using tuneable VUV radiation in the range 10.5-14.

New light on the imbroglio surrounding the CH isomers formed from ionized azulene and naphthalene using ion-molecule reactions.

Most polycyclic aromatic hydrocarbons (PAHs) can isomerize with internal energies near to or below the dissociation threshold. The CH group of ions, made up of the naphthalene (Naph) and the azulene (Azu) radical cations, is a prototypical example. CH isomers are important species in the growth kinetics and formation of complex organic molecules, and more generally fragments from larger PAHs, yet information about CH structures is scarce and contradictory.

HO˙ and OH reactivity furan: experimental low energy absolute cross sections for modeling radiation damage.

Radiotherapy is one of the most widespread and efficient strategies to fight malignant tumors. Despite its broad application, the mechanisms of radiation-DNA interaction are still under investigation. Theoretical models to predict the effects of a particular delivered dose are still in their infancy due to the difficulty of simulating a real cell environment, as well as the inclusion of a large variety of secondary processes.

Vacuum UV photodesorption of organics in the interstellar medium: an experimental study of formic acid HCOOH and methyl formate HCOOCH-containing ices.

Being a potential process that could explain gas phase abundances of so-called complex organic molecules (COMs) in the cold interstellar medium (ISM), the UV photon-induced desorption from organics-containing molecular ices has been experimentally studied. In this work, we focused on the observation of the photodesorbed products and the measurement of the associated photodesorption yields from pure and mixed molecular ices, each containing organic molecules whose detection has been achieved in the gas phase of the cold ISM, namely formic acid HCOOH and methyl formate HCOOCH. Each molecule, in pure ice or in ice mixed with CO or water, was irradiated at 15 K with monochromatic vacuum UV photons in the 7-14 eV range using synchrotron radiation from the SOLEIL synchrotron facility, DESIRS beamline.

Monitoring the Light-induced Isomerisation of the Prototypical Polycyclic Aromatic Hydrocarbons C H through Ion-Molecule Reactions.

Structural rearrangements in ions are essential for understanding the composition and evolution of energetic and chemically active environments. This study explores the interconversion routes for simple polycyclic aromatic hydrocarbons, namely naphthalene and azulene radical cations (C H ), by combining mass spectrometry and vacuum ultraviolet tunable synchrotron radiation through the chemical monitoring technique. Products of ion-molecule reactions are used to probe C H structures that are formed as a function of their internal energies.

Structural Elucidation of C H Using Chemical Reaction Monitoring: Charge Transfer Versus Bond Forming Reactions.

Mass spectrometry is a powerful tool but when used on its own, without specific activation of ions, the ion mass is the single observable and the structural information is absent. One way of retrieving this information is by using ion-molecule reactions. We propose a general method to disentangle isomeric structures by combining mass spectrometry, tunable synchrotron light source, and quantum-chemistry calculations.

Study of the Reactivity of CHCOOH and COOH Ions with CHNH: Evidence of the Formation of New Peptide-like C(O)-N Bonds.

Acetamide, a small organic compound containing a peptide bond, was observed in the interstellar medium, but reaction pathways leading to the formation of this prebiotic molecule remain uncertain. We investigated the possible formation of a peptide-like bond from the reaction between acetic acid (CH-COOH) and methylamine (CH-NH) that were identified in the interstellar medium. From an experimental point of view, a quadrupole/octopole/quadrupole mass spectrometer was used in combination with synchrotron radiation as a tunable source of VUV photons for monitoring the reactivity of selected ions.

State-Selected Reactivity of Carbon Dioxide Cations ( ) With Methane.

The reactivity of with CD has been experimentally investigated for its relevance in the chemistry of plasmas used for the conversion of CO in carbon-neutral fuels. Non-equilibrium plasmas are currently explored for their capability to activate very stable molecules (such as methane and carbon dioxide) and initiate a series of reactions involving highly reactive species (e.g.

Vibronic structure of the cyanobutadiyne cation. I. VUV photoionization study of HCN.

We report the vacuum-ultraviolet threshold-photoelectron spectrum of HCN recorded over a wide spectral range, from 84 000 to 120 000 cm, with a 120 cm spectral resolution, better than what was achieved in previous photoelectron studies, and with mass selectivity. The adiabatic ionization potential of cyanobutadiyne is measured at 85 366 (±40) cm. Assignment of the vibrational bands of the four lowest electronic states XΠ, AΠ, BΣ, and CΠ are performed, supported by high level ab initio calculations which are fully detailed in Paper II [B.

Effects of collision energy and vibrational excitation of CH cations on its reactivity with hydrocarbons: But-2-yne CHCCCH as reagent partner.

The methyl carbocation is ubiquitous in gaseous environments, such as planetary ionospheres, cometary comae, and the interstellar medium, as well as combustion systems and plasma setups for technological applications. Here we report on a joint experimental and theoretical study on the mechanism of the reaction CH + CHCCCH (but-2-yne, also known as dimethylacetylene), by combining guided ion beam mass spectrometry experiments with ab initio calculations of the potential energy hypersurface. Such a reaction is relevant in understanding the chemical evolution of Saturn's largest satellite, Titan.

Experimental and ab initio characterization of HCN vibronic structure. I. Synchrotron-based threshold photo-electron spectroscopy.

Threshold-photoionization spectroscopy of cyanoacetylene (HCN) and its N isotopologue has been investigated in the vacuum-ultraviolet range with a synchrotron-based experiment allowing to record threshold-photoelectron spectrum and photoion yield over a large energy range (from 88 500 to 177 500 cm, i.e., from 11 to 22 eV).

Is the Reaction of C3N(-) with C2H2 a Possible Process for Chain Elongation in Titan's Ionosphere?

The reaction of C3N(-) with acetylene was studied using three different experimental setups, a triple quadrupole mass spectrometer (Trento), a tandem quadrupole mass spectrometer (Prague), and the "CERISES" guided ion beam apparatus at Orsay. The process is of astrophysical interest because it can function as a chain elongation mechanism to produce larger anions that have been detected in Titan's ionosphere by the Cassini Plasma Spectrometer. Three major products of primary processes, C2H(-), CN(-), and C5N(-), have been identified, whereby the production of the cyanide anion is probably partly due to collisional induced dissociation.

Threshold photoelectron spectroscopy of unstable N-containing compounds: Resolution of ΔK subbands in HNCO(+) and vibrational resolution in NCO(.).

The threshold photoelectron spectra (TPES) of two unstable nitrogen-containing species, HNCO and NCO, were recorded utilizing vacuum ultraviolet synchrotron radiation. Both are intermediates in combustion processes and play a role in the removal of nitrogen oxides from exhaust gases. The rovibronic structure of the first band in the TPES of HNCO(+) was analyzed within the framework of an orbital ionization model, and the resolved structure of the origin band was assigned to ΔK subbands.

Reactions of State-Selected Atomic Oxygen Ions O(+)((4)S, (2)D, (2)P) with Methane.

An experimental study has been carried out on the reactions of state selected O(+)((4)S, (2)D, (2)P) ions with methane with the aims of characterizing the effects of both the parent ion internal energy and collision energy on the reaction dynamics and determining the fate of oxygen species in complex media, in particular the Titan ionosphere. Absolute cross sections and product velocity distributions have been determined for the reactions of (16)O(+) or (18)O(+) ions with CH4 or CD4 from thermal to 5 eV collision energies by using the guided ion beam (GIB) technique. Dissociative photoionization of O2 with vacuum ultraviolet (VUV) synchrotron radiation delivered by the DESIRS beamline at the SOLEIL storage ring and the threshold photoion photoelectron coincidence (TPEPICO) technique are used for the preparation of purely state-selected O(+)((4)S, (2)D, (2)P) ions.

UV photodesorption of interstellar CO ice analogues: from subsurface excitation to surface desorption.

Carbon monoxide is after H(2) the most abundant molecule identified in the interstellar medium (ISM), and is used as a major tracer for the gas phase physical conditions. Accreted at the surface of water-rich icy grains, CO is considered to be the starting point of a complex organic--presumably prebiotic--chemistry. Non-thermal desorption processes, and especially photodesorption by UV photons, are seen as the main cause that drives the gas-to-ice CO balance in the colder parts of the ISM.

The photoionisation of propargylene and diazopropyne.

The photoionisation of the C(3)H(2) isomer propargylene was studied using synchrotron radiation and coincidence techniques. An adiabatic ionisation energy (IE(ad)) of 8.99 ± 0.