Physical Sciences and Mathematics | Open Access Articles

Microsolvation Of Anions By Molecules Forming Ch∙∙X- Hydrogen Bonds, Steve Scheiner, Binod Nepal

Chemistry and Biochemistry Faculty Publications

Various anions were surrounded by n molecules of CF₃H, which was used as a prototype CH donor solvent, and the structures and energies studied by M06-2X calculations with a 6-31+G∗∗ basis set. Anions considered included the halides F^-, Cl^-, Br^- and I^-, as well as those with multiple proton acceptor sites: CN^-, NO₃ ^-, HCOO^-, CH₃COO^-, HSO₄ ^-, H₂PO₄ ^-, and anions with higher charges SO₄ ^2-, HPO₄ ^2- and PO_{4 …}

Go to article

In Situ Measurements And Modeling Of Reactive Trace Gases In A Small Biomass Burning Plume, M. Muller, B. Anderson, A. Beyersdorf, J. H. Crawford, G. Diskin, P. Eichler, A. Fried, F. N. Keutsch, T. Mikoviny, K. L. Thornhill, J. G. Walega, A. J. Weinheimer, M. Yang, Robert Yokelson, A. Wisthaler

Chemistry and Biochemistry Faculty Publications

An instrumented NASA P-3B aircraft was used for airborne sampling of trace gases in a plume that had emanated from a small forest understory fire in Georgia, USA. The plume was sampled at its origin for deriving emission factors and followed ~ 13.6 km downwind for observing chemical changes during the first hour of atmospheric aging. The P-3B payload included a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS), which measured non-methane organic gases (NMOGs) at unprecidented spatio-temporal resolution (10m/0.1 s). Quantitative emission data are reported for CO₂, CO, NO, NO₂, HONO, NH₃ and 16 NMOGs (formaldehyde, methanol, …

Go to article

Cobalt-Centred Boron Molecular Drums With The Highest Coordination Number In The Cob16− Cluster, Ivan A. Popov, Tian Jian, Gary V. Lopez, Alexander I. Boldyrev, Lai-Sheng Wang

Chemistry and Biochemistry Faculty Publications

The electron deficiency and strong bonding capacity of boron have led to a vast variety of molecular structures in chemistry and materials science. Here we report the observation of highly symmetric cobalt-centered boron drum-like structures of CoB16⁻, characterized by photoelectron spectroscopy and ab initio calculations. The photoelectron spectra display a relatively simple spectral pattern, suggesting a high symmetry structure. Two nearly degenerate isomers with D8d(I) and C4v (II) symmetries are found computationally to compete for the global minimum. These drum-like structures consist of two B8 rings sandwiching a cobalt atom, which has the highest …

Go to article

Biomass Burning Emissions And Potential Air Quality Impacts Of Volatile Organic Compounds And Other Trace Gases From Temperate Fuels Common In The United States, J. B. Gilman, B. M. Lerner, W. C. Kuster, P. D. Goldan, C. Warneke, P. R. Veres, J. M. Roberts, J. A. De Gouw, I. R. Burling, Robert Yokelson

Chemistry and Biochemistry Faculty Publications

A comprehensive suite of instruments was used to quantify the emissions of over 200 organic gases, including methane and volatile organic compounds (VOCs), and 9 inorganic gases from 56 laboratory burns of 18 different biomass fuel types common in the southeastern, southwestern, or northern United States. A gas chromatograph-mass spectrometer (GC-MS) provided extensive chemical detail of discrete air samples collected during a laboratory burn and was complemented by real-time measurements of organic and inorganic species via an open-path Fourier transform infrared spectrometer (OP-FTIR) and 3 different chemical ionization-mass spectrometers. These measurements were conducted in February 2009 at the U.S. Department …

Go to article

Investigating The Links Between Ozone And Organic Aerosol Chemistry In A Biomass Burning Plume From A Prescribed Fire In California Chaparral, M. J. Alvarado, C. R. Lonsdale, Robert Yokelson, Sheryl Kashi Akagi, H. Coe, J. S. Craven, E. V. Fischer, G. R. Mcmeeking, J. H. Seinfeld, T. Soni, J. W. Taylor, D. R. Weise, C. E. Wold

Chemistry and Biochemistry Faculty Publications

Within minutes after emission, complex photochemistry in biomass burning smoke plumes can cause large changes in the concentrations of ozone (O3) and organic aerosol (OA). Being able to understand and simulate this rapid chemical evolution under a wide variety of conditions is a critical part of forecasting the impact of these fires on air quality, atmospheric composition, and climate. Here we use version 2.1 of the Aerosol Simulation Program (ASP) to simulate the evolution of O₃ and secondary organic aerosol (SOA) within a young biomass burning smoke plume from the Williams prescribed fire in chaparral, which was sampled over …

Go to article

Revealing Important Nocturnal And Day-To-Day Variations In Fire Smoke Emissions Through A Multiplatform Inversion, Pablo E. Saide, David A. Peterson, Arlindo Da Silva, Bruce Anderson, Luke D. Ziemba, Glenn Diskin, Glen Sachse, Johnathan Hair, Carolyn Butler, Marta Fenn, Jose L. Jimenez, Pedro Campuzano-Jost, Anne E. Perring, Joshua P. Schwarz, Milos Z. Markovic, Phil Russell, Jens Redemann, Yohei Shinozuka, David G. Streets, Fang Yan, Jack Dibb, Robert Yokelson, O. Brian Toon, Edward Hyer, Gregory R. Carmichael

Chemistry and Biochemistry Faculty Publications

We couple airborne, ground-based, and satellite observations; conduct regional simulations; and develop and apply an inversion technique to constrain hourly smoke emissions from the Rim Fire, the third largest observed in California, USA. Emissions constrainedwithmultiplatform data show notable nocturnal enhancements (sometimes over a factor of 20), correlate better with daily burned area data, and are a factor of 2–4 higher than a priori estimates, highlighting the need for improved characterization of diurnal profiles and day-to-day variability when modeling extreme fires. Constraining only with satellite data results in smaller enhancements mainly due to missing retrievals near the emissions source, suggesting that …

Go to article

The Infrared Spectrum Of The He-C2d2 Complex, N. Moazzen-Ahmadi, A. R. W. Mckellar, Berta Fernandez, David Farrelly

Chemistry and Biochemistry Faculty Publications

Spectra of the helium-acetylene complex are elusive because this weakly bound system lies close to the free rotor limit. Previously, limited assignments of He–C2D2 transitions in the R(0) region of the ν3 fundamental band (≈2440 cm⁻¹) were published. Here, new He–C2D2 infrared spectra of this band are obtained using a tunable optical parametric oscillator laser source to probe a pulsed supersonic slit jet expansion from a cooled nozzle, and the analysis is extended to the weaker and more difficult P(1) and R(1) regions. A term value approach is used to obtain a consistent set of “experimental” energy levels. …

Go to article

Identification And Quantification Of Gaseous Organic Compounds Emitted From Biomass Burning Using Two-Dimensional Gas Chromatography–Time-Of-Flight Mass Spectrometry, L. E. Hatch, W. Luo, J. F. Pankow, Robert Yokelson, C. Stockwell, K. C. Barsanti

Chemistry and Biochemistry Faculty Publications

The current understanding of secondary organic aerosol (SOA) formation within biomass burning (BB) plumes is limited by the incomplete identification and quantification of the non-methane organic compounds (NMOCs) emitted from such fires. Gaseous organic compounds were collected on sorbent cartridges during laboratory burns as part of the fourth Fire Lab at Missoula Experiment (FLAME-4) and analyzed by two-dimensional gas chromatography-time-of-flight mass spectrometry (GC x GC-ToFMS). The sensitivity and resolving power of GC x GC-ToFMS allowed the acquisition of the most extensive data set of BB NMOCs to date, with measurements from 708 positively or tentatively identified compounds. Estimated emission factors …

Go to article

Intramolecular S···O Chalcogen Bond As Stabilizing Factor In Geometry Of Substituted Phenyl-Sf3 Molecules, Vincent De Paul Nziko, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

Density functional methods are used to examine the geometries and energetics of molecules containing a phenyl ring joined to the trigonal bipyramidal SF3 framework. The phenyl ring has a strong preference for an equatorial position. This preference remains when one or two ether -CH2OCH3 groups are added to the phenyl ring, ortho to SF3, wherein an apical structure lies nearly 30 kcal/mol higher in energy. Whether equatorial or apical, the molecule is stabilized by a S···O chalcogen bond, sometimes augmented by CH···F or CH···O H-bonds. The strength of the intramolecular S···O bond is estimated to lie in the range between …

Go to article

Characterization Of Biomass Burning Emissions From Cooking Fires, Peat, Crop Residue, And Other Fuels With High-Resolution Proton-Transfer-Reaction Time-Of-Flight Mass Spectrometry, C. Stockwell, P. Veres, J. Williams

Chemistry and Biochemistry Faculty Publications

We deployed a high-resolution proton-transferreaction time-of-flight mass spectrometer (PTR-TOF-MS) to measure biomass-burning emissions from peat, crop residue, cooking fires, and many other fire types during the fourth Fire Lab at Missoula Experiment (FLAME-4) laboratory campaign. A combination of gas standard calibrations and composition sensitive, mass-dependent calibration curves was applied to quantify gas-phase non-methane organic compounds (NMOCs) observed in the complex mixture of fire emissions. We used several approaches to assign the best identities to most major “exact masses”, including many high molecular mass species. Using these methods, approximately 80–96% of the total NMOC mass detected by the PTR-TOFMS and Fourier …

Go to article

Observations And Analysis Of Organic Aerosol Evolution In Some Prescribed Fire Smoke Plumes, A. A. May, T. Lee, G. R. Mcmeeking, Sheryl Kashi Akagi, A. P. Sullivan, S. P. Urbanski, Robert Yokelson, S. M. Kreidenweis

Chemistry and Biochemistry Faculty Publications

Open biomass burning is a significant source of primary air pollutants such as particulate matter and non-methane organic gases. However, the physical and chemical atmospheric processing of these emissions during transport is poorly understood. Atmospheric 5 transformations of biomass burning emissions have been investigated in environmental chambers, but there have been limited opportunities to investigate these transformations in the atmosphere. In this study, we deployed a suite of real-time instrumentation on a Twin Otter aircraft to sample smoke from prescribed fires in South Carolina, conducting measurements at both the source and downwind to character10 ize smoke evolution with atmospheric aging. …

Go to article

Physical Sciences and Mathematics Commons^™

Full-Text Articles in Physical Sciences and Mathematics

Microsolvation Of Anions By Molecules Forming Ch∙∙X- Hydrogen Bonds, Steve Scheiner, Binod Nepal

Chemistry and Biochemistry Faculty Publications

In Situ Measurements And Modeling Of Reactive Trace Gases In A Small Biomass Burning Plume, M. Muller, B. Anderson, A. Beyersdorf, J. H. Crawford, G. Diskin, P. Eichler, A. Fried, F. N. Keutsch, T. Mikoviny, K. L. Thornhill, J. G. Walega, A. J. Weinheimer, M. Yang, Robert Yokelson, A. Wisthaler

Chemistry and Biochemistry Faculty Publications

Cobalt-Centred Boron Molecular Drums With The Highest Coordination Number In The Cob16− Cluster, Ivan A. Popov, Tian Jian, Gary V. Lopez, Alexander I. Boldyrev, Lai-Sheng Wang

Chemistry and Biochemistry Faculty Publications

Chemistry and Biochemistry Faculty Publications

Chemistry and Biochemistry Faculty Publications

Chemistry and Biochemistry Faculty Publications

The Infrared Spectrum Of The He-C2d2 Complex, N. Moazzen-Ahmadi, A. R. W. Mckellar, Berta Fernandez, David Farrelly

Chemistry and Biochemistry Faculty Publications

Identification And Quantification Of Gaseous Organic Compounds Emitted From Biomass Burning Using Two-Dimensional Gas Chromatography–Time-Of-Flight Mass Spectrometry, L. E. Hatch, W. Luo, J. F. Pankow, Robert Yokelson, C. Stockwell, K. C. Barsanti

Chemistry and Biochemistry Faculty Publications

Intramolecular S···O Chalcogen Bond As Stabilizing Factor In Geometry Of Substituted Phenyl-Sf3 Molecules, Vincent De Paul Nziko, Steve Scheiner

Chemistry and Biochemistry Faculty Publications

Characterization Of Biomass Burning Emissions From Cooking Fires, Peat, Crop Residue, And Other Fuels With High-Resolution Proton-Transfer-Reaction Time-Of-Flight Mass Spectrometry, C. Stockwell, P. Veres, J. Williams

Chemistry and Biochemistry Faculty Publications

Observations And Analysis Of Organic Aerosol Evolution In Some Prescribed Fire Smoke Plumes, A. A. May, T. Lee, G. R. Mcmeeking, Sheryl Kashi Akagi, A. P. Sullivan, S. P. Urbanski, Robert Yokelson, S. M. Kreidenweis

Chemistry and Biochemistry Faculty Publications