Arnold Fox

Carbene chemistry of cations: the chemistry of the carbene cation :C3H+ in the gas phase

Preparation de C 3 H + a partir du propene dans un spectrometre de masse SIFT et etude de ses reactions avec divers substrats (H 2 , CO, H 2 O, H 2 S, CO 2 , CH 4 , CH 3 OH, C 2 H 4 )

Laboratory measurements of gas‐phase reactions of polyatomic carbon ions C+n(n=1–6) and CnH+(n=2–5) with carbon monoxide

The selected‐ion flow tube (SIFT) technique has been employed in the study of reactions of carbon monoxide with the polyatomic carbon cations C+n(n=1−6) and CnH+(n=2–5) at 296±2 K in helium buffer gas at ∼0.34 Torr and 1.1×1016 atoms cm−3. The polyatomic carbon cations were generated by electron impact on a suitable parent molecule. Carbon monoxide was observed to add rapidly to C+n(n=2–6) twice in succession to form polyatomic carbon monoxide and dioxide cations, and once to CnH+ to form polyatomic carbon monoxide cations. Further additions did not occur with measurable specific rates. This remarkable behavior is attributed to double bond formation at the terminal carbon atoms of the polyatomic carbon cations. The specific rate for the addition of CO was observed to vary with the size of the polyatomic carbon cation, increasing to a maximum for reactions with five atoms in the reacting ion. This trend is attributed to an increase in the lifetime of the intermediate addition complex.

Formation of the high-energy isomer HSiO+ by chemical reaction in the gas phase

The high-energy isomer HSiO+ of protonated SiO has been generated by a fast O-atom transfer reaction between SiH* and N20 in helium and hydrogen buffer gases at 0.35 Torr and 295 k 2 K. Formation of HSiO* by O-atom transfer proceeds in competition with formation of the ground-state SiOH+ isomer, which is formally an Insertion reaction. Other insertion reactions were observed in the reactions of SiH+ with COa and SO*. The mechanism of insertion is rationalized in terms of sequential Oatom transfer and isomerization of HSiO+ to SiOH+ within the intermediate complex, where the isomerization may be achieved via a proton shuttle within the complex or unimolecularly, when suffkient excessenergy is available in the initial O-atom transfer. The high-energy isomer HSiO* does not convert to SiOH+ by reaction with H2 at the operating conditions of the experiments.

Chemical Pathways from Atomic Silicon Ions to Silicon Carbides and Oxides

Ion/molecule reactions initiated by ground-state atomic silicon ions are described which lead to Si-C and Si-O bond formation. They are viewed as the first steps in the chemical pathways leading from atomic silicon to the formation of silicon carbide and oxide molecules of the type which may be precursors for the formation of silicon carbide and silicate grain particles in carbon-rich and oxygen-rich astrophysical environments.

Laboratory Studies of Extraterrestrial Chemistry Initiated by Atomic Silicon Ions in the Gas Phase

Gas-phase chemistry initiated by atomic silicon ions occurs in a variety of extraterrestrial environments including diffuse interstellar clouds,1 dense interstellar clouds,2 and the atmospheres of certain stars.3 Reliable observational evidence for extraterrestrial molecules containing Si exists for SiO, SiS and SiC2 but is limited otherwise, in contrast to evidence which has been obtained for larger numbers of molecules containing less abundant elements. This lack of observational evidence is partly due to the lack of experimental spectral information for relevant silicon-containing molecules. Such information is difficult to obtain in the terrestrial laboratory. Also, one needs to know which silicon-containing molecules to search for. Suggestions have been made in the past,4 but the basis of these suggestions is somewhat obscure. Here we explore experimentally the kinds of silicon-containing molecules which may be produced via the chemistry initiated by atomic silicon ions in the gas phase.