The reactions of the OH radicals and the Cl atoms with 3-hydroxy 2-butanone (3H2B) and 4-hydroxy 2-butanone (4H2B) were investigated in the gas-phase using relative rate method. The kinetic study on the OH-reactions was carried out using a Pyrex atmospheric chamber at 600-760 Torr of purified air. The temperature ranges were 298-338 K for 3H2B and 278-333 K for 4H2B. A slight negative dependence of the rate coefficients behavior was observed and the Arrhenius expressions obtained are (in cm 3 molecule-1 s-1): k 3H2B(OH) = (1.250.20)× 10-12 exp(61250/T) and k 4HB (OH) = (7.50 2.0) ×10-12 exp(19620/T). Rate coefficients for the gas-phase reactions of Cl atoms with 3H2B and 4H2B were measured using an atmospheric simulation chamber made of Teflon at 298 ± 3 K and 760 Torr. The obtained rate coefficients (in cm 3 molecule-1 s-1) were (4.90 0.45) ×10-11 and (1.45 0.15) ×10-10 for 3H2B and 4H2B, respectively. The obtained data are presented, compared to those reported in the literature and the reactivity trends discussed. The estimated tropospheric lifetimes obtained in this work suggest that once emitted into the atmosphere, 3H2B and 4H2B will be oxidized near the emission sources.

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The UV absorption cross-sections of 2,3-pentanedione and 2,4-pentanedione were measured and their reactions with OH were investigated in the gas-phase using a relative rate method. A temperature dependence of the rate coefficients was observed for both reactions over the temperature range 298 -338 K. This work provides the first UV cross-section in the gas phase for 2,4-pentanedione and the first kinetic data for the reaction of 2,3-pentanedione with OH radicals as a function of temperature. The tropospheric lifetimes obtained in this work suggest that once emitted into the atmosphere, these species could be quickly degraded close to their emission sources.

The gas-phase reactions of the bare tungsten cation W+ with silane have been investigated using Fourier-Transform Ion Cyclotron Resonance mass spectrometry. Dehydrogenation of a first molecule leads to the formation of WSiH2 +. This ion is itself reactive with a second silane molecule, this time through elimination of 2H2, to form WSi2H2 +. A similar reaction follows, yielding WSi3H2 + as the next product ion, which itself leads to both WSi4H4 + and WSi4H2 +. This seems to initiate two parallel reaction sequences, yielding WSi10H6 + as the major final product, together with a minor amount of WSi10H4 +. CID experiments on the products of the first three reactions were carried out to aid in their structural elucidation. Ab initio calculations at the CASSCF level have been performed in order to derive optimum structures for the first two product ions WSiH2 + and WSi2H2 +, and for the non-observed intermediate WSi2H4 +. The results show that structural isomerism exists for these three ions, due to the versatile bonding capabilities of W+ and Si. The ground state of WSiH2 + is a high-spin (sextet) silylene complex in which there is a dative bond between SiH2 and the metal. For WSi2H4 + there are two low-energy isomers, a covalently bonded metal disilene three-membered ring with a quartet spin state, and a datively bonded metal silylsilylene in a high-spin sextet. It is proposed that the successive ions formed have compact structures, and that the reaction sequence ends when the metal gets trapped into a silicon cage, or alternatively when it no longer has enough nonbonding electrons to insert exothermically into a Si−H bond of a further silane molecule.