Richard I. Martinez

Mass spectrometric detection of dioxirane, H2COO, and its decomposition products, H2 and CO, from the reaction of ozone with ethylene

Abstract Dioxirane has been detected in the gas phase, by means of photoionization mass spectrometry, as a product of the low temperature reaction of ozone with ethylene. Hydrogen and carbon monoxide are found to be products of the decomposition of dioxirane. The significance of these observations to atmospheric chemistry is discussed.

Gas‐phase reaction of SO2 with a Criegee intermediate in the presence of water vapor

Abstract A reaction scheme is proposed to explain the H2SO4 aerosol formation experimentally observed in O3‐alkene‐SO2 systems in terms of adduct formation between SO2 and a Criegee intermediate. The reaction scheme also provides the basis for a homogeneous gas‐phase flue‐gas desulfurization process.

Products of the reaction of hydroxyl radicals with trans-2-butene in the presence of oxygen and nitrogen dioxide

Abstract The reactions of hydroxy-substituted alkyl radicals, formed as secondary products in the reaction of ozone with trans-2-butene, have been identified in photoionization mass spectrometry studies, using acetaldehyde and nitrogen dioxide as free-radical scavengers. Products derived from 2-hydroxy-1-methylpropl in the absence of scavengers include 2,3-butanedione (diacetyl), 3-hydroxy-2-butanone (acetoin),and 2,3-butanediol. In the presence of added acetaldehyde or nitrogen dioxide, the formation of these products is suppressed. In addition, with added nitrogen dioxide, new products are formed which have been identified as a series of oxoalkyl and hydroxy-substituted-alkyl nitrates and peroxynitrates. These observations may have an important bearing on the chemistry of photochemical smog.

The role of the Criegee intermediate in the matrix thermoluminescence study of the CH2+O2 reaction

The identification by Lee and Pimentel [J. Chem. Phys., 74, 4851 (1981)] of two new progressions of formic acid arising from the reaction of CH2 with O2 in an argon matrix provides the first direct identification of excited formic acid as an intermediate product of this reaction. Their observations provide further evidence that the reaction of CH2 with O2 probably proceeds to products through the initial formation of the dioxmethylene adduct H2ĊOȮ (a Criegee intermediate) which then rearranges to the excited formic acid through the CH2O2 intermediates dioxirane and methylenebis (oxy). (AIP)

Absolute cross-section measurements in XQQ instruments: Ar+ + N2 → Ar + N+2

Abstract The energy dependence of the cross-section, σ(E), for the asymmetric near-resonant charge-transfer reaction Ar+ + N2 → Ar + N+2 was measured in the NBS triple quadrupole (QQQ) tandem mass spectrometer. For P ⋍ 0.04–0.35 mtorr and E ⋍ 5–60 eV (LAB) [the range of collision energies used for collisionally activated dissociation (CAD)], identical σE values were measured from both the rate of reactant ion decay and the rate of product ion formation. Therefore, these σE values are substantially free from kinetic interferences (i.e. no back reactions, no impurity reactions, no scattering losses, minimal fringing fields, no mass discrimination, well-defined gas target, etc.). Moreover, there is probably no significant systematic error in our measurements of the absolute σE values for Ar+ + N2 → Ar + N+2 because the σE values we measured with this same technique for Ne+ + Ne → Ne + Ne+ and Ar+ + Ar → Ar + Ar+ agreed well with literature values obtained with several well-established techniques.

The NBS triple quadrupole tandem mass spectrometer

A detailed description is provided of a triple quadrupole (QQQ) tandem mass spectrometer (MS/MS) which is kinetically well behaved and can be configured to use either a molecular beam target (type A) or collision chamber (type B) configuration. Its unique capabilities are being used to explore design criteria essential for (i) absolute cross‐section measurements, and for (ii) the development of standardized operating conditions for generic, instrument‐independent spectral databases for collisionally activated dissociation (CAD).

Validation of absolute target thickness calibrations in a QQQ instrument by measuring absolute total cross-sections of Ne+ (Ne, Ne) Ne+

Abstract Total cross-sections, σ( E ), for the symmetric (resonant) charge transfer reaction Ne + + Ne → Ne + Ne + were measured in our triple-quadrupole (QQQ) tandem mass spectrometer for collision energies E coll ⋍ 5–60 eV (LAB coordinates). This is the range of energies typically used for collision-induced dissociation (CID) in QQQ instruments. We measured identical σ( E ) from both the rate of reactant ion decay and the rate of product ion formation. This validates that our QQQ instrument is kinetically well behaved. Our σ( E ), for E ⋍ 5–60 eV and P ⋍ 0.04–1 mtorr are in excellent agreement with the Rapp-Francis theory as corrected by Dewangan. Our kinetic method provides a means whereby the absolute target thickness [(actual path length traversed by the ion) × (effective number density of the CID target)] of gas targets can be accurately calibrated in situ for collision energies in the range of ca. 5–60 eV (LAB). Knowledge of target thicknesses is essential for the development of generic CID spectral libraries generated in different types of QQQ instruments [i.e. collision chamber and molecular beam targets]. An interlaboratory round robin test protocol is being formulated to assess the utility of our method for standardization of generic operating parameters. Letters of inquiry from prospective participants may be sent to NBS.

Stopped-flow study of the gas-phase reactions of ozone with organic sulfides: thiirane

Abstract The autocatalytic reaction of ozone with thiirane has been studied at 296 K and 1.1 kPa (8 Torr) The specific rate of primary attack of ozone on thurane is immeasurably slow ( k 4 cm 3 mol −1 s −1 ). The major products observed are C 2 H 4 , SO 2 , H 2 CO and CO 2 . A free-radical chain mechanism is suggested to account for these observations.

Excited-neutral-metastable SO2 formation in the , O3-olefin-SO2, and active nitrogen-SO2 systems

Abstract Long-liied (τ > 10 −3 s), electronically-excited ( E * > 4 eV) neutral metastables, whose formation was attributed to the presence of SO 2 , were observed in the three titled systems. Their possible identity as collisionally-accessed metastable states of the normal , cyclic , or superoxide isomers of SO 2 is discussed.

Acid precipitation: The role of O3‐alkene‐SO2 systems in the atmospheric conversion of SO2 to H2SO4 aerosol

Abstract The atmospheric conversion of SO2 to H2SO4 aerosol is discussed in the context of O3‐alkene‐SO2 reactions and a mechanism is proposed.