Photodissociation spectroscopy and dynamics of the CH(2)CFO radical

Alexandra A. Hoops, Jason R. Gascooke, Kathryn E. Kautzman, Ann Elise Faulhaber, and Daniel M. Neumar

Photodissociation of the Propargyl (C3D3) Radicals at 248 nm and 193 nm

The photodissociation of perdeuterated propargyl (D{sub 2}CCCD) and propynyl (D{sub 3}CCC) radicals was investigated using fast beam photofragment translational spectroscopy. Radicals were produced from their respective anions by photodetachment at 540 nm and 450 nm (below and above the electron affinity of propynyl). The radicals were then photodissociated by 248 nm or 193 nm light. The recoiling photofragments were detected in coincidence with a time- and position-sensitive detector. Three channels were observed: D{sub 2} loss, CD + C{sub 2}D{sub 2}, and CD{sub 3} + C{sub 2}. Obervation of the D loss channel was incompatible with this experiment and was not attempted. Our translational energy distributions for D{sub 2} loss peaked at nonzero translational energy, consistent with ground state dissociation over small (< 1 eV) exit barriers with respect to separated products. Translational energy distributions for the two heavy channels peaked near zero kinetic energy, indicating dissociation on the ground state in the absence of exit barriers

PHOTODISSOCIATION OF SMALL I−^{-}(H2{_2}O)n{_n} CLUSTERS EXCITED TO THE CHARGE TRANSFER TO SOLVENT STATE

Author Institution: The Department of Chemistry, the University of California, Berkeley, and the Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720Anions in polar solvents typically display a broad absorption band in the UV due to the transfer of charge from the anion to the solvent. These charge transfer to solvent states (CTTS) have been the subject of many studies in the bulk and more recently in clusters. Although I$^{-}$(H${_2}$O)${_n}$ clusters have been studied both theoretically as well as experimentally, there is still some uncertainty as to the nature of the cluster analog of the CTTS state. Results presented here describe experiments performed using the fast beam photofragment coincident imaging technique to determine the main photodissociation products and translational energy distributions (P(E${_T}$)) of I$^{-}$(H${_2}$O)${_n}$ clusters excited to the CTTS state. A cool beam of I$^{-}$(H${_2}$O)${_n}$ (n = 2-5) clusters is accelerated, mass selected and excited to the CTTS state. The resulting photofragments strike a time-and-position-sensitive detector, enabling the calculation of product masses as well as the corresponding P(E${_T}$). In all cases, two channels are observed. The main channel is a 2-body process producing neutral I and (H${_2}$O)${_n}$ products, and the minor channel is a 3-body process forming neutral I, (H${_2}$O)${_{n-1}}$ and H${_2}$O products. Both channels impart little translational energy to the photofragments for all cluster sizes. Photodissociation is believed to occur following autodetachment of the cluster, producing neutral products

Light-Absorbing Oligomer Formation in Secondary Organic Aerosol from Reactive Uptake of Isoprene Epoxydiols

Secondary organic aerosol (SOA) produced from reactive uptake and multiphase chemistry of isoprene epoxydiols (IEPOX) has been found to contribute substantially (upward of 33%) to the fine organic aerosol mass over the Southeastern U.S. Brown carbon (BrC) in rural areas of this region has been linked to secondary sources in the summer when the influence of biomass burning is low. We demonstrate the formation of light-absorbing (290 < λ < 700 nm) SOA constituents from reactive uptake of <i>trans</i>-β-IEPOX onto preexisting sulfate aerosols as a potential source of secondary BrC. IEPOX-derived BrC generated in controlled chamber experiments under dry, acidic conditions has an average mass absorption coefficient of ∼300 cm² g^–1. Chemical analyses of SOA constituents using UV–visible spectroscopy and high-resolution mass spectrometry indicate the presence of highly unsaturated oligomeric species with molecular weights separated by mass units of 100 (C₅H₈O₂) and 82 (C₅H₆O) coincident with the observations of enhanced light absorption, suggesting such oligomers as chromophores, and potentially explaining one source of humic-like substances (HULIS) ubiquitously present in atmospheric aerosol. Similar light-absorbing oligomers were identified in fine aerosol collected in the rural Southeastern U.S., supporting their atmospheric relevance and revealing a previously unrecognized source of oligomers derived from isoprene that contributes to ambient fine aerosol mass

Fast beam studies of I(2)(-) and I(2)(-) (.) Ar photodissociation

Copyright © 2003 Elsevier Science B.VThe photodissociation dynamics of bare I₂⁻ and I₂⁻ • Ar at 413 and 390 nm have been investigated using a fast beam instrument coupled with a new photofragment coincidence imaging detector. Results from the application of this technique to the dissociation of I₂⁻ and I₂⁻ • Ar yielded the dissociation energy of I₂⁻ (D₀(I₂⁻)=1.012±0.008 eV) and I₂⁻–Ar binding energy (D0(I₂⁻–Ar)=45±8 meV). The experiments show that at these wavelengths, I₂⁻ • Ar undergoes three-body dissociation to I⁻ + I* + Ar, with very low momentum in the Ar atom and unequal momentum partitioning between the two I atoms.Alexandra A. Hoops, Jason R. Gascooke, Ann Elise Faulhaber, Kathryn E. Kautzman and Daniel M. Neumar