OH radical formation from the ozone reaction with isoprene, α‐pinene, and methyl vinyl ketone were measured using the recently developed small‐ratio relative‐rate technique. This method uses small amounts of fast‐reacting aromatics and aliphatic ethers to trace OH formation. Measured OH yields were 0.25±0.06, 0.70±0.17, and 0.16±0.05 for isoprene, α‐pinene, and methyl vinyl ketone, respectively. The levels of biogenic alkenes necessary to contribute a non‐negligible fraction of new OH, HO2, and RO2 radicals are briefly discussed.

Abstract. A series of experiments investigating the formation of OH radicals from O3-alkene reactions are described. Pairs of OH tracer compounds--aromatic and aliphatic hydrocarbons--were added to O3-alkene mixtures in small quantities. Under these conditions, a large fraction of the tracer is consumed, resulting in a much larger signal than in experiments using excess tracer. The average decay ratios of tracer pairs in 30 experiments were within 7% of those predicted by literature rate constants for tracer-OH reactions, strongly supporting the hypothesis that OH is formed directly from 03 reaction with alkenes.

The complex dielectric constants of n-alkanes with two to seven carbon atoms have been measured. The measurements were conducted using a slotted-line technique at 1.2 GHz and at atmospheric pressure. The temperature was varied from the melting point to the boiling point of the respective alkanes. The real part of the dielectric constant was found to decrease with increasing temperature and correlate with the change in the molar volume. An upper limit to all the loss tangents was established at 0.001. The complex dielectric constants of a few mixtures of liquid alkanes were also measured at room temperature. For a pentane-octane mixture the real part of the dielectric constant could be explained by the Clausius-Mosotti theory. For the mixtures of n-hexane-ethylacetate and n-hexane-acetone the real part of the dielectric constants could be explained by the Onsager theory extended to mixtures. The dielectric constant of the n-hexane-acetone mixture displayed deviations from the Onsager theory at the highest fractions of acetone. The dipole moments of ethylacetate and acetone were determined for dilute mixtures using the Onsager theory and were found to be in agreement with their accepted gas-phase values. The loss tangents of the mixtures exhibited a linear relationship with the volume fraction for low concentrations of the polar liquids.

The reaction of the methyl cation with hydrogen cyanide is revisited. We have confidence that we have resolved a long standing apparent contradiction of experimental results. A literature history is presented along with one new experiment and a re-examination of an old experiment. In this present work it is shown that all of the previous studies had made consistent observations. Yet, each of the previous studies failed to observe all of the information present. The methyl cation does react with HCN by radiative association, a fact which had been in doubt. The product ions formed in the two-body and three-body processes react differently with HCN. The collisionally stabilized association product formed by a three-body mechanism, does not react with HCN and is readily detected in the experiments. The radiatively stabilized association product, formed by a slow two-body reaction, is not detected because it reacts with HCN by a fast proton transfer reaction forming the protonated HCN ion. Previous studies either ‘‘lost’’ this product in the extremely large protonated HCN signal that is always present when HCN is used, or discounted it for various reasons. We have been able to show by ion cyclotron resonance (ICR) techniques (both FT-ICR and tandem ICR-dempster-ICR) that the radiative association product does react with the HCN to form the protonated HCN ion.

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