C. Rebrion-Rowe

Ultralow temperature kinetics of neutral–neutral reactions. The technique and results for the reactions CN+O2 down to 13 K and CN+NH3 down to 25 K

An entirely new experimental method is described which enables the rate constants of neutral–neutral gas‐phase reactions to be measured at ultralow temperatures. The measurements are made by applying the pulsed laser photolysis (PLP), laser‐induced fluorescence (LIF) technique of studying the kinetics of free radical reactions in the ultracold environment provided by the gas flow in a Cinetique de Reaction en Ecoulement Supersonique Uniforme (CRESU) apparatus. The experimental method is described in some detail and its application and limitations are discussed. Results are reported for the reactions of CN radicals with O2 and NH3. For reaction (1) between CN and O2 data are reported for the temperature range T=13–295 K and the rate constants are well‐matched by the expression k1(T)=(2.49±0.17)×10−11 (T/298)(−0.63±0.04) cm3 molecule−1 s−1. For reaction (2) between CN and NH3, rate constants in the temperature range T=25–295 K fit the expression k2(T)=(2.77±0.67)×10−11 (T/298)(−1.14±0.15) cm3 molecule−1 s−1...

Ultra‐low temperature kinetics of neutral–neutral reactions: The reaction CN+O2 down to 26 K

A new method is described which enables the measurement for the first time of the rates of neutral–neutral gas‐phase reactions at temperatures down to 26 K (and in the future, below). Results for the reaction of CN radicals with O2 are presented and discussed in terms of current theoretical treatments.

The dissociative recombination of hydrocarbon ions. I. Light alkanes

Rate coefficients for the dissociative recombination of a series of hydrocarbon ions derived from normal alkanes have been measured using the FALP-MS technique. Despite the increasing complexity of the ions along the series, the measured rate coefficients are found to be remarkably similar having values between 5.5 and 8.3×10−7 cm3 s−1.

The Si(

The rate coecient of the reaction Si( 3 PJ )+O 2! SiO +Oh as been measured at temperatures down to 15 Ku sing aC RESU (Cinetique de R eaction en Ecoulement Supersonique Uniforme) apparatus coupled with the PLP-LIF (Pulsed Laser Photolysis { Laser Induced Fluorescence) technique. The temperature dependence of the rate coecient is well tted using the expression: 1:7210 10 (T /300 K) 0:53 exp( 17 K=T )c m 3 molecule 1 s 1 in the temperature range 15{300 K. The silicon chemistry in interstellar clouds is reviewed and possible consequences of our study are stressed.

^\mathsf3

A series of measurements of the rate coefficient for the dissociative recombination (DR) of has been recorded. A value of was found for ions that are vibrationally cold. This is somewhat smaller than that measured previously by this group. The difference is ascribed to aerodynamic effects which affected our earlier measurement that have been eliminated in the present work. Results for and DR are also reported.

PJ) + O

Dissociative recombination reactions of a number of cyclic ions, derived from ion-molecule reactions involving acetylene as parent molecule and of protonated butane derived from reactions involving ethylene have been studied. It is found that the recombination rate coefficient does not seem to be much affected by the substitution of functional groups for hydrogen atoms in the cyclic cases. Also, protonated butane has a rate coefficient very similar to that for protonated methane.

_\mathsf2

A storage ring measurement of the rate coefficient for the production of neutral Ar in e + ArH + collisions is described. It is found that the recombination rate is too small to measure at low centre-of-mass energies but the combined rate coefficient for dissociative recombination and dissociative excitation increases above 2.5 eV displaying peaks centred at 7.5 eV, 16 and 26 eV. Calculated potential energy curves for the ground and excited states of ArH + are presented and these aid in the elucidation of the recombination and excitation processes observed at higher energies. The implications for plasma modelling are discussed.

reaction: A fast source of SiO at very low temperature; CRESU measurements and interstellar consequences

Rate coefficients for the reaction of ground-state silicon atoms Si(3PJ) with acetylene and ethylene have been measured at temperatures down to 15 K. The experiments have been performed in a continuous flow CRESU (Cinetique de Reaction en Ecoulement Supersonique Uniforme) apparatus using pulsed laser photolysis of Si(CH3)4 to generate Si(3PJ) atoms and laser-induced fluorescence to observe the kinetic decay of the atoms and hence determine the rate coefficients. Both reactions are found to be fast, and the reaction rates show a very mild dependence on temperature. The rate coefficients match the expressions k(Si+C2H2)=(2.6±0.6)10−10(T/300)−(0.71±0.24) exp(−(29±10)/T) cm3 molecule−1 s−1 and k(Si+C2H4)=(3.7±0.3)10−10(T/300)−(0.34±0.10) exp(−(16±4)/T) cm3 molecule−1 s−1 in the temperature range 15–300 K. The nature of the products and the similarities of the carbon and silicon chemistry are discussed.

New FALP-MS measurements of , and dissociative recombination

Abstract Branching ratios for CC bond breaking during the dissociative recombination of C4H9+ and C4H5+ ions, produced from n-butane gas in a Nielsen source, have been measured using the merged beam method at the ASTRID storage ring. These results show that while C4H9+ recombines to form C4 and C3+C products, C4H5+ recombines to form C4 and C2+C2 products. A discussion of how these fragmentation patterns may be related to the isomeric forms of the ions undergoing recombination is presented.

The dissociative recombination of hydrocarbon ions. II. Alkene and alkyne derived species

Experimental results are presented from an experiment in which ionization created by a high energy X-ray synchrotron radiation beam intersecting an ethylene diffusion flame is measured. The ionization signal is believed to arise from X-ray absorption by aggregated soot particles. Comparisons are made between these ionization profiles and those that are a result of natural flame ionization. Visible light absorption measurements were also performed to determine the soot volume fraction in the beam and the results compared with the X-ray induced signals.