An experimental and theoretical investigation of the N(D) + CH (benzene) reaction with implications for the photochemical models of Titan.

We report on a combined experimental and theoretical investigation of the N(D) + CH (benzene) reaction, which is of relevance in the aromatic chemistry of the atmosphere of Titan. Experimentally, the reaction was studied (i) under single-collision conditions by the crossed molecular beams (CMB) scattering method with mass spectrometric detection and time-of-flight analysis at the collision energy () of 31.8 kJ mol to determine the primary products, their branching fractions (BFs), and the reaction micromechanism, and (ii) in a continuous supersonic flow reactor to determine the rate constant as a function of temperature from 50 K to 296 K.

Low-temperature kinetics for the N + NO reaction: experiment guides the way.

The reaction N(S) + NO(XΠ) → O(P) + N(XΣ+g) plays a pivotal role in the conversion of atomic to molecular nitrogen in dense interstellar clouds and in the atmosphere. Here we report a joint experimental and computational investigation of the N + NO reaction with the aim of providing improved constraints on its low temperature reactivity. Thermal rates were measured over the 50 to 296 K range in a continuous supersonic flow reactor coupled with pulsed laser photolysis and laser induced fluorescence for the production and detection of N(S) atoms, respectively.

Reaction N(D) + CHCCH (Allene): An Experimental and Theoretical Investigation and Implications for the Photochemical Models of Titan.

We report on a combined experimental and theoretical investigation of the N(D) + CHCCH (allene) reaction of relevance in the atmospheric chemistry of Titan. Experimentally, the reaction was investigated (i) under single-collision conditions by the crossed molecular beams (CMB) scattering method with mass spectrometric detection and time-of-flight analysis at the collision energy ( ) of 33 kJ/mol to determine the primary products and the reaction micromechanism and (ii) in a continuous supersonic flow reactor to determine the rate constant as a function of temperature from 50 to 296 K. Theoretically, electronic structure calculations of the doublet CHN potential energy surface (PES) were performed to assist the interpretation of the experimental results and characterize the overall reaction mechanism.

Kinetic Study of the Gas-Phase O(D) + CHOH and O(D) + CHCN Reactions: Low-Temperature Rate Constants and Atomic Hydrogen Product Yields.

Atomic oxygen in its first excited singlet state, O(D), is an important species in the photochemistry of several planetary atmospheres and has been predicted to be a potentially important reactive species on interstellar ices. Here, we report the results of a kinetic study of the reactions of O(D) with methanol, CHOH, and acetonitrile, CHCN, over the 50-296 K temperature range. A continuous supersonic flow reactor is used to attain these low temperatures coupled with pulsed laser photolysis and pulsed laser-induced fluorescence to generate and monitor O(D) atoms, respectively.

An Experimental and Theoretical Investigation of the Gas-Phase C(P) + NO Reaction. Low Temperature Rate Constants and Astrochemical Implications.

The reaction between atomic carbon in its ground electronic state, C(P), and nitrous oxide, NO, has been studied below room temperature due to its potential importance for astrochemistry, with both species considered to be present at high abundance levels in a range of interstellar environments. On the experimental side, we measured rate constants for this reaction over the 50-296 K range using a continuous supersonic flow reactor. C(P) atoms were generated by the pulsed photolysis of carbon tetrabromide at 266 nm and were detected by pulsed laser-induced fluorescence at 115.

Experimental and theoretical studies of the gas-phase reactions of O(D) with HO and DO at low temperature.

Here we report the results of an experimental and theoretical study of the gas-phase reactions between O(D) and HO and O(D) and DO at room temperature and below. On the experimental side, the kinetics of these reactions have been investigated over the 50-127 K range using a continuous flow Laval nozzle apparatus, coupled with pulsed laser photolysis and pulsed laser induced fluorescence for the production and detection of O(D) atoms respectively. Experiments were also performed at 296 K in the absence of a Laval nozzle.

Tunneling Enhancement of the Gas-Phase CH + CO Reaction at Low Temperature.

The rates of numerous activated reactions between neutral species increase at low temperatures through quantum mechanical tunneling of light hydrogen atoms. Although tunneling processes involving molecules or heavy atoms are well known in the condensed phase, analogous gas-phase processes have never been demonstrated experimentally. Here, we studied the activated CH + CO → HCO + CO reaction in a supersonic flow reactor, measuring rate constants that increase rapidly below 100 K.

Experimental and theoretical studies of the N(D) + H and D reactions.

This study reports the results of an experimental and theoretical investigation of the N(2D) + H2 and N(2D) + D2 reactions at room temperature and below. On the experimental side, a supersonic flow (Laval nozzle) reactor was employed to measure rate constants for these processes at temperatures as low as 127 K. N(2D) was produced indirectly by pulsed laser photolysis and these atoms were detected directly by pulsed laser induced fluorescence in the vacuum ultraviolet wavelength region.

A kinetic study of the N(D) + CH reaction at low temperature.

Electronically excited nitrogen atoms N(D) are important species in the photochemistry of N based planetary atmospheres such as Titan. Despite this, few N(D) reactions have been studied over the appropriate low temperature range. During the present work, rate constants were measured for the N(D) + ethene (CH) reaction using a supersonic flow reactor at temperatures between 50 K and 296 K.

Rate constants for the N(D) + CH reaction over the 50-296 K temperature range.

The reactions of metastable atomic nitrogen N(D) are important processes in the gas-phase chemistry of several planetary atmospheres. Here we present a combined experimental and theoretical investigation of the N(D) + acetylene reaction due to its potential significance for the photochemistry of Titan's atmosphere. Experimentally, a continuous supersonic flow reactor was used to study this reaction over the 50-296 K temperature range employing pulsed laser photolysis and vacuum ultraviolet laser induced fluorescence to produce and detect N(D) atoms, respectively.

Experimental and Theoretical Study of the O(D) + HD Reaction.

This work addresses the kinetics and dynamics of the gas-phase reaction between O(D) and HD molecules down to low temperature. Here, measurements were performed by using a supersonic flow (Laval nozzle) reactor coupled with pulsed laser photolysis for O(D) production and pulsed-laser-induced fluorescence for O(D) detection to obtain rate constants over the 50-300 K range. Additionally, temperature-dependent branching ratios (OD + H/OH + D) were obtained experimentally by comparison of the H/D atom atom yields with those of a reference reaction.

Oxygen fractionation in dense molecular clouds.

We have developed the first gas-grain chemical model for oxygen fractionation (also including sulphur fractionation) in dense molecular clouds, demonstrating that gas-phase chemistry generates variable oxygen fractionation levels, with a particularly strong effect for NO, SO, O, and SO. This large effect is due to the efficiency of the neutral O + NO, O + SO, and O + O exchange reactions. The modeling results were compared to new and existing observed isotopic ratios in a selection of cold cores.

Low-Temperature Rate Constants and Product-Branching Ratios for the C(D) + HO Reaction.

The gas-phase reaction between atomic carbon in its first electronically excited D state and water has been studied over the 50-296 K temperature range using a supersonic flow apparatus. C(D) atoms were produced by pulsed ultraviolet multiphoton dissociation of carbon tetrabromide; a process that also generates ground-state atomic carbon C(P). The reaction was followed by detecting product H-atoms by pulsed vacuum ultraviolet laser-induced fluorescence.

Conical intersection-regulated intermediates in bimolecular reactions: Insights from C(D) + HD dynamics.

The importance of conical intersections (CIs) in electronically nonadiabatic processes is well known, but their influence on adiabatic dynamics has been underestimated. Here, through combined experimental and theoretical studies, we show that CIs induce a barrier and regulate conversion from a precursor metastable intermediate (CI-R) to a deep well one. This results in bond-selective activation, influencing the adiabatic dynamics markedly in the C(D) + HD reaction.

A low temperature investigation of the N(D) + CH, CH and CH reactions.

The gas-phase reactions between metastable nitrogen atoms, N(D) and saturated hydrocarbons CH, CH and CH have been investigated using a supersonic flow reactor over the 296-75 K temperature range. N(D) was generated as a product of the C(P) + NO → N(D) + CO reaction, with C(P) atoms created in situ by pulsed laser photolysis of CBr. The kinetics of N(D) loss were followed by vacuum ultraviolet laser induced fluorescence.

A low temperature investigation of the gas-phase N(D) + NO reaction. Towards a viable source of N(D) atoms for kinetic studies in astrochemistry.

The gas-phase reaction of metastable atomic nitrogen N(2D) with nitric oxide has been investigated over the 296-50 K temperature range using a supersonic flow reactor. As N(2D) could not be produced photolytically in the present work, these excited state atoms were generated instead through the C(3P) + NO → N(2D) + CO reaction while C(3P) atoms were created in situ by the 266 nm pulsed laser photolysis of CBr4 precursor molecules. The kinetics of N(2D) atoms were followed on-resonance by vacuum ultraviolet laser induced fluorescence at 116.

Rate Constants and H-Atom Product Yields for the Reactions of O(D) Atoms with Ethane and Acetylene from 50 to 296 K.

The gas phase reactions of atomic oxygen in its first excited state with ethane and acetylene have been investigated in a continuous supersonic flow reactor over the temperature range from 50 to 296 K. O(D) atoms were produced by the pulsed laser photolysis of ozone at 266 nm. Two different types of experiments, kinetics measurements and H-atom product yield determinations, were performed by detecting O(D) atoms and H(S) atoms, respectively, by vacuum ultraviolet laser-induced fluorescence.

Kinetics of the Gas-Phase O(D) + CO and C(D) + CO Reactions over the 50-296 K Range.

The kinetics of the reactions of CO with atomic oxygen and atomic carbon in their first excited singlet states have been studied at room temperature and below using the Laval nozzle reactor method. O(D) and C(D) atoms were created in situ by the 266 nm pulsed laser photolysis of O and CBr precursor molecules, respectively. While O(D) atoms were detected directly by vacuum ultraviolet laser-induced fluorescence at 115 nm, C(D) atoms were followed indirectly through a chemical tracer method.

Experimental and theoretical investigation of the temperature dependent electronic quenching of O(D) atoms in collisions with Kr.

The kinetics and dynamics of the collisional electronic quenching of O(D) atoms by Kr have been investigated in a joint experimental and theoretical study. The kinetics of quenching were measured over the temperature range 50-296 K using the Laval nozzle method. O(D) atoms were prepared by 266 nm photolysis of ozone, and the decay of the O(D) concentration was monitored through vacuum ultraviolet fluorescence at 115.

A combined theoretical and experimental investigation of the kinetics and dynamics of the O(D) + D reaction at low temperature.

The O(D) + H reaction is a prototype for simple atom-diatom insertion type mechanisms considered to involve deep potential wells. While exact quantum mechanical methods can be applied to describe the dynamics, such calculations are challenging given the numerous bound quantum states involved. Consequently, efforts have been made to develop alternative theoretical strategies to portray accurately the reactive process.

Kinetic and Product Study of the Reactions of C(D) with CH and CH at Low Temperature.

The reactions of atomic carbon in its first excited D state with both CH and CH have been investigated using a continuous supersonic flow reactor over the 50-296 K temperature range. C(D) atoms were generated in situ by the pulsed laser photolysis of CBr at 266 nm. To follow the reaction kinetics, product H atoms were detected by vacuum ultraviolet laser-induced fluorescence at 121.

Low-Temperature Experimental and Theoretical Rate Constants for the O(D) + H Reaction.

In the present joint experimental and theoretical study, we report thermal rate constants for the O(D) + H reaction within the 50-300 K temperature range. Experimental kinetics measurements were performed using a continuous supersonic flow reactor coupled with pulsed laser photolysis for O(D) production and pulsed laser-induced fluorescence in the vacuum ultraviolet wavelength range (VUV LIF) for O(D) detection. Theoretical rate constants were obtained using the ring polymer molecular dynamics (RPMD) approach over the two lowest potential energy surfaces 1A' and 1A″, which possess barrierless and thermally activated energy profiles, respectively.

An experimental and theoretical investigation of the C(D) + D reaction.

In a previous joint experimental and theoretical study of the barrierless chemical reaction C(D) + H at low temperatures (300-50 K) [K. M. Hickson, J.

Theoretical and experimental investigations of rate coefficients of O(D) + CH at low temperature.

The rate coefficients of the barrierless O(D) + CH reaction are determined both theoretically and experimentally at 50-296 K. For the calculations, ring polymer molecular dynamics (RPMD) simulations are performed on the basis of a new neural network potential energy surface (PES) in the reactant asymptotic part. Only the reactant asymptotic part of the PES is constructed because of its barrierless and exothermic properties.