Photolysis of CH3CHO at 248 nm: Evidence of triple fragmentation from primary quantum yield of CH3 and HCO radicals and H atoms

Radical quantum yields have been measured following the 248 nm photolysis of acetaldehyde, CH3CHO. HCO radical and H atom yields have been quantified by time resolved continuous wave Cavity Ring Down Spectroscopy in the near infrared following their conversion to HO2 radicals by reaction with O2. The CH3 radical yield has been determined using the same technique following their conversion into CH3O2. Absolute yields have been deduced for HCO radicals and H atoms through fitting of time resolved HO2 profiles, obtained under various O2 concentrations, to a complex model, while the CH3 yield has been determined relative to the CH3 yield from 248 nm photolysis of CH3I. Time resolved HO2 profiles under very low O 2 concentrations suggest that another unknown HO2 forming reaction path exists in this reaction system besides the conversion of HCO radicals and H atoms by reaction with O2. HO2 profiles can be well reproduced under a large range of experimental conditions with the following quantum yields: CH3CHO+hν248nm → CH 3CHO*, CH3CHO* → CH3+HCO φ1a = 0.125±0.03, CH3CHO* → CH 3+H+CO φ1e = 0.205±0.04, CH 3CHO* o2→ CH3CO+HO2 φ1f = 0.07±0.01. The CH3O2 quantum yield has been determined in separate experiments as φCH3 = 0.33 ± 0.03 and is in excellent agreement with the CH3 yields derived from the HO2 measurements considering that the triple fragmentation (R1e) is an important reaction path in the 248 nm photolysis of CH3CHO. From arithmetic considerations taking into account the HO2 and CH3 measurements we deduce a remaining quantum yield for the molecular pathway: CH3CHO* → CH 4+CO φ1b = 0.6. All experiments can be consistently explained with absence of the formerly considered pathway: CH 3CHO* → CH3CO+H φ1c = 0. © 2014 AIP Publishing LLC.Fil: Pranay Morajkar. University Of Lille.; FranciaFil: Bossolasco, Adriana Gabriela. University Of Lille.; Francia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Schoemaecker, Coralie. University Of Lille.; FranciaFil: Fittschen, Christa. University Of Lille.; Franci

The life-career class in the public school curriculum

Thesis (M.A)--Boston Universit

Potential energy surfaces for atomic oxygen reactions: Formation of singlet and triplet biradicals as primary reaction products with unsaturated organic molecules

The experimental study of the interaction of atomic oxygen with organic polymer films under LEO conditions has been hampered by the inability to conduct detailed experiments in situ. As a result, studies of the mechanism of oxygen atom reactions have relied on laboratory O-atom sources that do not fully reproduce the orbital environment. For example, it is well established that only ground electronic state O atoms are present at LEO, yet most ground-based sources are known to produce singlet O atoms and molecules and ions in addition to O(3P). Engineers should not rely on such facilities unless it can be demonstrated either that these different O species are inert or that they react in the same fashion as ground state atoms. Ab initio quantum chemical calculations have been aimed at elucidating the biradical intermediates formed during the electrophilic addition of ground and excited-state O atoms to carbon-carbon double bonds in small olefins and aromatic molecules. These biradicals are critical intermediates in any possible insertion, addition and elimination reaction mechanisms. Through these calculations, we will be able to comment on the relative importance of these pathways for O(3P) and O(1D) reactions. The reactions of O atoms with ethylene and benzene are used to illustrate the important features of the mechanisms of atomic oxygen reaction with unsaturated organic compounds and polymeric materials

Evolution of red wines II. An assessment of the role of acetaldehyde

Factors influencing formation and utilisation of acetaldehyde during red vinification have been examined, with emphasis on its production during primary fermentation and depletfon during early maturation.Acetaldehyde concentrations in new wines were controlled at predictably low levels by addition of SO2 at 30- 50 mg/l before fermentation. There was no appreciable effect from yeast strain, pH or temperature on acetaldehyde production. Significant decrease in acetaldehyde, a-ketoglutaric acid and pyruvic acid, with release of free SO2, occurred during malolactic fermentation. The rate of acetaldehyde consumption in sterile-filtered wine was increased at higher te·mperature and decreased by the presence of free SO2 at high levels. Progressive change in pigment composition of new wines was not influenced by variation in bound acetaldehyde within the range 2-103 mg/l.Acetaldehyde concentration also decreased in a majority of red wines during conservation in commercial cellars. Increases were attributed to abnormal conditions of wine exposure to air. lt was concluded that acetaldehyde formation in wine is probably a surface phenomenon, involving autoxidation of ethanol at the wine interface with atmospheric oxygen. Increase in acetaldehyde during vinification was considered to be adverse in relation to sensory properties and stability of red wine

Letter to Mary Sibley from William Potts, May 26, 1840

Transcript of letter to Mary Sibley from William Potts, May 26, 1840. Potts discusses issues related to the local Presbyterian Church