Emission resulting from KrF laser (248 nm) multiphoton dissociation of HgBr2 was resolved in the ... more Emission resulting from KrF laser (248 nm) multiphoton dissociation of HgBr2 was resolved in the 460-510 nm region. Vibrational analysis of the HgBr(B2∑-X2∑) transition was also determined. The formation of electronically excited HgBr(B2∑) radicals was induced by two-photon dissociation of HgBr2 via a real intermediate state. The role of added inert gas on the observed emission was also examined, and the following order of efficiency was found N2, Ar, Xe and Ne.
OH, Cl and O3 kinetics and IR spectra of (CF3)2CCH2 utilized to estimate tropospheric lifetimes,... more OH, Cl and O3 kinetics and IR spectra of (CF3)2CCH2 utilized to estimate tropospheric lifetimes, radiative efficiencies, global warming potentials, estimated photochemical ozone creation potentials and tropospheric oxidation end-products.
Molecular beam techniques are commonly used to obtain detailed information about reaction dynamic... more Molecular beam techniques are commonly used to obtain detailed information about reaction dynamics and kinetics of gas-surface interactions. These experiments are traditionally performed in vacuum and the dynamic state of surfaces under ambient conditions is thereby excluded from detailed studies. Herein we describe the development and demonstration of a new vacuum-gas interface that increases the accessible pressure range in environmental molecular beam (EMB) experiments. The interface consists of a grating close to a macroscopically flat surface, which allows for experiments at pressures above 1 Pa including angularly resolved measurements of the emitted flux. The technique is successfully demonstrated using key molecular beam experiments including elastic helium and inelastic water scattering from graphite, helium and light scattering from condensed adlayers, and water interactions with a liquid 1-butanol surface. The method is concluded to extend the pressure range and flexibili...
Water uptake on aerosol and cloud particles in the atmosphere modifies their chemistry and microp... more Water uptake on aerosol and cloud particles in the atmosphere modifies their chemistry and microphysics with important implications for climate on Earth. Here, we apply an environmental molecular beam (EMB) method to characterize water accommodation on ice and organic surfaces. The adsorption of surface-active compounds including short-chain alcohols, nitric acid, and acetic acid significantly affects accommodation of D2O on ice. n-Hexanol and n-butanol adlayers reduce water uptake by facilitating rapid desorption and function as inefficient barriers for accommodation as well as desorption of water, while the effect of adsorbed methanol is small. Water accommodation is close to unity on nitric-acid- and acetic-acid-covered ice, and accommodation is significantly more efficient than that on the bare ice surface. Water uptake is inefficient on solid alcohols and acetic acid but strongly enhanced on liquid phases including a quasi-liquid layer on solid n-butanol. The EMB method provides unique information on accommodation and rapid kinetics on volatile surfaces, and these studies suggest that adsorbed organic and acidic compounds need to be taken into account when describing water at environmental interfaces.
Journal of the Chemical Society, Faraday Transactions, 1996
ABSTRACT The reaction of Cl atoms with dimethyl disulfide, CH3SSCH3, was studied in the gas phase... more ABSTRACT The reaction of Cl atoms with dimethyl disulfide, CH3SSCH3, was studied in the gas phase and over the temperature range 273–363 K with the very low pressure reactor (VLPR) technique. The reaction proceeds via two competing pathways: (a) hydrogen atom abstraction that produces CH3SSCH2 radicals, with a rate given by the expression k1a=(1.83 ± 0.08)× 10–10 exp [–(2.43 ± 0.21)/RT] cm3 molecule–1 s–1, (R in kJ mol–1 K–1, 2σ uncertainty); and (b) an intermediate adduct CH3S(Cl)SCH3 formation channel, which further leads to CH3SCl and CH3S products, its rate is given by the expression k1b=(5.17 ± 0.32)× 10–11 exp [(3.39 ± 0.29)/RT] cm3 molecule–1 s–1. The branching ratio k1a/k1b was found to be 0.35 at room temperature and low pressure conditions.
Emission resulting from KrF laser (248 nm) multiphoton dissociation of HgBr2 was resolved in the ... more Emission resulting from KrF laser (248 nm) multiphoton dissociation of HgBr2 was resolved in the 460-510 nm region. Vibrational analysis of the HgBr(B2∑-X2∑) transition was also determined. The formation of electronically excited HgBr(B2∑) radicals was induced by two-photon dissociation of HgBr2 via a real intermediate state. The role of added inert gas on the observed emission was also examined, and the following order of efficiency was found N2, Ar, Xe and Ne.
OH, Cl and O3 kinetics and IR spectra of (CF3)2CCH2 utilized to estimate tropospheric lifetimes,... more OH, Cl and O3 kinetics and IR spectra of (CF3)2CCH2 utilized to estimate tropospheric lifetimes, radiative efficiencies, global warming potentials, estimated photochemical ozone creation potentials and tropospheric oxidation end-products.
Molecular beam techniques are commonly used to obtain detailed information about reaction dynamic... more Molecular beam techniques are commonly used to obtain detailed information about reaction dynamics and kinetics of gas-surface interactions. These experiments are traditionally performed in vacuum and the dynamic state of surfaces under ambient conditions is thereby excluded from detailed studies. Herein we describe the development and demonstration of a new vacuum-gas interface that increases the accessible pressure range in environmental molecular beam (EMB) experiments. The interface consists of a grating close to a macroscopically flat surface, which allows for experiments at pressures above 1 Pa including angularly resolved measurements of the emitted flux. The technique is successfully demonstrated using key molecular beam experiments including elastic helium and inelastic water scattering from graphite, helium and light scattering from condensed adlayers, and water interactions with a liquid 1-butanol surface. The method is concluded to extend the pressure range and flexibili...
Water uptake on aerosol and cloud particles in the atmosphere modifies their chemistry and microp... more Water uptake on aerosol and cloud particles in the atmosphere modifies their chemistry and microphysics with important implications for climate on Earth. Here, we apply an environmental molecular beam (EMB) method to characterize water accommodation on ice and organic surfaces. The adsorption of surface-active compounds including short-chain alcohols, nitric acid, and acetic acid significantly affects accommodation of D2O on ice. n-Hexanol and n-butanol adlayers reduce water uptake by facilitating rapid desorption and function as inefficient barriers for accommodation as well as desorption of water, while the effect of adsorbed methanol is small. Water accommodation is close to unity on nitric-acid- and acetic-acid-covered ice, and accommodation is significantly more efficient than that on the bare ice surface. Water uptake is inefficient on solid alcohols and acetic acid but strongly enhanced on liquid phases including a quasi-liquid layer on solid n-butanol. The EMB method provides unique information on accommodation and rapid kinetics on volatile surfaces, and these studies suggest that adsorbed organic and acidic compounds need to be taken into account when describing water at environmental interfaces.
Journal of the Chemical Society, Faraday Transactions, 1996
ABSTRACT The reaction of Cl atoms with dimethyl disulfide, CH3SSCH3, was studied in the gas phase... more ABSTRACT The reaction of Cl atoms with dimethyl disulfide, CH3SSCH3, was studied in the gas phase and over the temperature range 273–363 K with the very low pressure reactor (VLPR) technique. The reaction proceeds via two competing pathways: (a) hydrogen atom abstraction that produces CH3SSCH2 radicals, with a rate given by the expression k1a=(1.83 ± 0.08)× 10–10 exp [–(2.43 ± 0.21)/RT] cm3 molecule–1 s–1, (R in kJ mol–1 K–1, 2σ uncertainty); and (b) an intermediate adduct CH3S(Cl)SCH3 formation channel, which further leads to CH3SCl and CH3S products, its rate is given by the expression k1b=(5.17 ± 0.32)× 10–11 exp [(3.39 ± 0.29)/RT] cm3 molecule–1 s–1. The branching ratio k1a/k1b was found to be 0.35 at room temperature and low pressure conditions.
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