Electronic state spectroscopy of C2Cl4

Estimate of the C-Cl photoionization cross section and absolute photoionization cross sections of chlorinated organic compounds

Chlorinated organic compounds are prominently used for industrial production, but their vapors and emission byproducts can cause detrimental effects to human health and the environment. To accurately quantify organochlorine compounds, the absolute photoionization cross section of tetrachloroethylene, chlorobenzene, 1,2-dichlorobenzene, and chloroacetone are measured using multiplexed synchrotron photoionization mass spectrometry at the Advanced Light Source at Lawrence Berkeley National Laboratory. These measurements allow for the estimation of the C-Cl photoionization cross section, increasing quantification accuracy of chlorinated emissions for kinetic modeling and pollutant mitigation. CBS-QB3 calculations of adiabatic ionization energies and thermochemical appearance energies are also presented and agree well with the experimental results.

Ozone Generation from a Germicidal Ultraviolet Lamp with Peak Emission at 222 nm

Recent interest in commercial devices containing germicidal ultraviolet lamps with a peak emission wavelength at 222 nm (GUV222) has focused on mitigating virus transmission indoors while posing minimum risk to human tissue. However, 222 nm light can produce ozone (O3) in air. O3 is an undesirable component of indoor air because of health impacts from acute to chronic exposure and its ability to degrade indoor air quality through oxidation chemistry. In seven four-hour experiments we measured O3 produced from a single filtered GUV222 lamp in a 31.5 m3 stainless steel chamber. Using an emission model, we determined an O3 generation rate of 19.4 ppbv h-1 ± 0.3 ppbv h-1 (equivalent to 1.22 mg h-1 ± 0.02 mg h-1). We estimated the fluence rate from the lamp using two methods: (1) chemical actinometry using tetrachloroethylene (actinometry) and (2) geometric projection of the irradiance field from radial and angular distribution measurements of the GUV222 lamp fluence (irradiance). Using the estimated lamp fluence rates of 2.2 μW cm-2 (actinometry) and 3.2 μW cm-2 (irradiance) we predicted O3 production in our chamber within 20 % of the average measured mixing ratio. Future studies should evaluate the indoor air quality impacts of GUV222 technologies.

Halocarbenes May Deplete Atmospheric Ozone

Photooxidation of tetrachloroethylene (PERC) and trichloroethylene (TCE) in simulated tropospheric smog chamber studies occurs with a time delay, accelerating simultaneous decreasing O3/chlorinated ethylene (CE) concentrations along with increasing CCl2O, which is attributed to CCl2 in the case of PERC and CCl2 or CHCl for TCE. The carbenes, chlorinated acetyl chlorides and CCl2O products may result from the rearrangement of the oxidised and/or excited oxidised CE, e.g. an epoxide. Analyses indicate scavenging experiments have not proved the existence of Cl atoms as being responsible for chlorinated acetyl chloride formation. Halocarbenes may form complexes with O3 which can undergo electron transfer (ET) and lead to dissociation of O3 to O2 and O and regeneration of carbene, resulting in a chain reaction. The direction of ET may be determined by the smallest differential HOMO–LUMO energy between the carbene and O3 which results in greater transition state stabilisation. Similarities in the reactions of O3 with carbenes and simple alkenes, nucleophilic carbenes with electron-poor alkenes and electrophilic carbene PhCCl with alkyl-substituted alkenes, i.e. (1) complex formation, (2) very low or negative activation energies and (3) the ability to undergo ET reactions with alkylalkenes are discussed. The possibility of the world-wide used perhalocarbons, e.g. perfluorinated carbons, hydroperhalocarbons, their halogenated replacements and starting materials degrading to halocarbenes which may degrade O3, is analysed.