Geert Moortgat - Academia.edu (original) (raw)
Papers by Geert Moortgat
The Journal of Organic Chemistry, 2011
Dilute mixtures of n-octanal in synthetic air (up to 100 ppm) were photolyzed with fluorescent UV... more Dilute mixtures of n-octanal in synthetic air (up to 100 ppm) were photolyzed with fluorescent UV lamps (275-380 nm) at 298 K. The main photooxidation products were 1-hexene, CO, vinyl alcohol, and acetaldehyde. The photolysis rates and the absolute quantum yields were found to be slightly dependent on the total pressure. At 100 Torr, Φ(100) = 0.41 ± 0.06, whereas at 700 Torr the total quantum yield was Φ(700) = 0.32 ± 0.02. Two decomposition channels were identified: the radical channel C(7)H(15)CHO → C(7)H(15) + HCO and the molecular channel C(7)H(15)CHO → C(6)H(12) + CH(2)═CHOH, having absolute quantum yields of 0.022 and 0.108 at 700 Torr. The product CH(2)═CHOH tautomerizes to acetaldehyde. Carbon balance data lower than unities suggest the existence of unidentified decomposition channel(s) which substantially contributes to the photolysis. On the basis of experimental and theoretical evidence, n-octanal photolysis predominantly proceeds to form Norrish type II products as the major ones.
The Journal of Physical Chemistry A, 2012
Dilute mixtures of n-butanal, 3-methylbutanal, and 3,3-dimethylbutanal in synthetic air, differen... more Dilute mixtures of n-butanal, 3-methylbutanal, and 3,3-dimethylbutanal in synthetic air, different N(2)/O(2) mixtures, and pure nitrogen (up to 100 ppm) were photolyzed with fluorescent UV lamps (275-380 nm) at 298 K. The main photooxidation products were ethene (n-butanal), propene (3-methylbutanal) or i-butene (3,3-dimethylbutanal), CO, vinylalcohol, and ethanal. The photolysis rates and the absolute quantum yields were found to be dependent on the total pressure of synthetic air but not of nitrogen. At 100 Torr, the total quantum yield Φ(100) = 0.45 ± 0.01 and 0.49 ± 0.07, whereas at 700 Torr, Φ(700) = 0.31 ± 0.01 and 0.36 ± 0.03 for 3-methylbutanal and 3,3-dimethybutanal, respectively. Quantum yield values for n-butanal were reported earlier by Tadić et al. (J. Photochem. Photobiol. A2001143, 169-179) to be Φ(100) = 0.48 ± 0.02 and Φ(700) = 0.32 ± 0.01. Two decomposition channels were identified: the radical channel RCHO → R + HCO (Norrish type I) and the molecular channel CH(3)...
Fine mode aerosol was collected on quartz fiber filters at several sites across Europe. These sam... more Fine mode aerosol was collected on quartz fiber filters at several sites across Europe. These samples were analyzed for carboxylic acids by liquid chromatography coupled to a hybrid (quadrupole and time-of-flight) mass spectrometer (LC/ MS/MS-TOF). A series of oxodicarboxylic acids (C 7 -C 11 ) was detected. Oxodicarboxylic acids are linear dicarboxylic acids with an additional carbonyl group. Previous measurements of these acids are scarce and their sources are largely unknown. Several structural isomers (different positions of the carbonyl group within the molecule) could be identified and differentiated by the combination of laboratory experiments and high mass accuracy measurements. The homologs with 9-11 carbon atoms were identified for the first time in atmospheric aerosol particles. The concentrations of oxodicarboxylic acids in ambient aerosol samples frequently exceeded those of the corresponding unsubstituted dicarboxylic acids. Oxodicarboxylic acids have been shown to be products of the reaction of dicarboxylic acids with OH radicals in chamber experiments and a reaction mechanism is proposed. Good correlation of oxodicarboxylic acid and hydroxyl radical concentrations was found at two measurement sites (Finland and Crete) of different geographic location and meteorological conditions. The ratios of individual isomers from the field samples are comparable to those of the laboratory experiments. The results of this study imply that the reaction of OH radicals and dicarboxylic acids is an important pathway for the production of oxodicarboxylic acids in the atmosphere. Oxodicarboxylic acids seem to be important intermediates in atmospheric oxidation processes of organic compounds. r
4-Oxopentanoic acid was characterized experimentally by electrospray ionization using a triple qu... more 4-Oxopentanoic acid was characterized experimentally by electrospray ionization using a triple quadrupole and time-of-flight analyzer hybrid system. This compound was chosen as a model substance for small organic compounds bearing an acetyl and a carboxyl group. Collision-induced dissociation experiments at different activation energies were performed to elucidate possible fragmentation pathways. These pathways were also studied on the theoretical level using density functional theory (DFT) B3LYP/6-311++G(3df,3pd)//B3LYP/6-31+G(d)+ZPVE calculations. CO2 ejection from the [M-H](-) anion of 4-oxopentanoic acid was observed and the fragmentation pathway studied by DFT reveals a new concerted mechanism for CO2 elimination accompanied by an intramolecular proton transfer within a pentagonal transition state structure. Successive elimination of water and CO from the [M-H](-) anion of 4-oxopentanoic acid was also observed. A rearrangement in the primary deprotonated ketene anion produced after water elimination was found on the theoretical level and leads to CO elimination from the primary product anion [M-H-H2O](-). Energy diagrams along the reaction coordinates of the fragmentation pathways are presented and discussed in detail. Mulliken charge distributions of some important structures are presented.
The objective of this work was to develop a method to determine the concentrations of higher orga... more The objective of this work was to develop a method to determine the concentrations of higher organic acids in snow samples. The target species are the homologous aliphatic α,ω-dicarboxylic acids from C 5 to C 13 , pinonic acid, pinic acid and phthalic acid. A preconcentration procedure utilizing solid phase extraction was developed and optimized using solutions of authentic standards. The influences of different parameters such as flow rate during extraction and the concentration of the eluent on the efficiency of the extraction procedure were investigated. The compounds of interest were separated by HPLC and detected by a quadrupole time-of-flight mass spectrometer (qTOF-MS). The recovery rate (extraction efficiency) of the extraction procedure was found to vary between 41% for tridecanedioic acid and 102% for adipic acid. The limits of detection were determined for all compounds and were between 0.9 nmol/L (dodecanedioic acid) and 29.5 nmol/L (pinonic acid). An exception is pinic acid, for which a considerably higher detection limit of 103.9 nmol/L was calculated. Snow samples were collected in December 2006 and January 2007 at the Fee glacier (Switzerland) from locations at heights from 3056 to 3580 m asl and from different depths within the snow layer. In total, the analysis of 61 single snow samples was performed, and the following compounds could be quantified: homologous aliphatic α,ωdicarboxylic acids with 5-12 carbon atoms and phthalic acid. Tridecanedioic acid, pinonic and pinic acid were identified in the samples but were not quantified due to their low concentrations. The three most abundant acids found in the molten snow samples were glutaric acid (C 5 -di; 3.90 nmol/L), adipic acid (C 6 -di; 3.35 nmol/L) and phthalic acid (Ph; 3.04 nmol/L).
The temperature dependence of secondary organic aerosol (SOA) formation from ozonolysis of β-pine... more The temperature dependence of secondary organic aerosol (SOA) formation from ozonolysis of β-pinene was studied in a flow reactor at 263 K-303 K and 1007 hPa under dry and humid conditions (0% and 26%-68% relative humidity, respectively). The observed SOA yields reached maximum values of 0.18-0.39 at high particle mass concentrations (M o ). Under dry conditions, the measurement data showed an overall increase in SOA yield with inverse temperature, but significant oscillatory deviations from the predicted linear increase with inverse temperature (up to 50% at high M o ) was observed. Under humid conditions the SOA yield exhibited a linear decrease with inverse temperature. For the atmospherically relevant concentration level of M o =10 µg m −3 and temperature range 263 K-293 K, the results from humid experiments in this study indicate that the SOA yield of β-pinene ozonolysis may be well represented by an average value of 0.15 with an uncertainty estimate of ±0.05. When fitting the measurement data with a twoproduct model, both the partitioning coefficients (K om,i ) and the stoichiometric yields (α i ) of the low-volatile and semivolatile model species were found to vary with temperature. The results indicate that not only the reaction product vapour pressures but also the relative contributions of different gasphase or multiphase reaction channels are strongly dependent on temperature and the presence of water vapour. In fact, the oscillatory positive temperature dependence observed under dry conditions and the negative temperature dependence observed under humid conditions indicate that the SOA yield is governed much more by the temperature and humidity dependence of the involved chemical reactions than by vapour
The temperature dependence of secondary organic aerosol (SOA) formation from ozonolysis of β-pine... more The temperature dependence of secondary organic aerosol (SOA) formation from ozonolysis of β-pinene was studied in a flow reactor at 263-303 K and 1007 hPa. The observed SOA yields were of similar magnitude as predicted by a two-product model based on detailed gas phase chemistry , reaching maximum values of 5 0.22-0.39 at high particle mass concentrations. However, the measurement data exhibited significant deviations (up to 50%) from the predicted linear dependence on inverse temperature. When fitting the measurement data with a two-product model, we found that both the partitioning coefficients (K om,i ) and the stoichiometric yields (α i ) of the low-volatile and semi-volatile species vary with temperature. The results indicate 10 that not only the reaction product vapour pressures but also the relative contributions of different gas-phase or multiphase reaction channels are dependent on temperature. We suggest that the modelling of secondary organic aerosol formation in the atmosphere needs to take into account the effects of temperature on the pathways and kinetics of the involved chemical reactions as well as on the gas-particle partitioning of 15 the reaction products. 20 vegetation emit large amounts of biogenic volatile organic compounds (BVOCs) (500-1800 Tg C yr −1 ). Besides isoprene monoterpenes are the most abundant BVOCs, and with an emission rate of 10-50 Tg C yr −1 β-pinene is the second most important monoterpene (Wiedinmyer et al., 2004). Biogenic secondary organic aerosol (SOA) are formed from oxidation of BVOCs in the atmosphere by O 3 , OH and NO 3 radicals, Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion
The Journal of Physical Chemistry, 1989
The ultraviolet absorption spectrum of the acetylperoxy radical was measured in the range 190-280... more The ultraviolet absorption spectrum of the acetylperoxy radical was measured in the range 190-280 nm. The radical was generated by flash photolysis of Clâ/CHâCHO/Oâ mixtures. The absorption spectrum was calibrated against the HOâ radical generated in the Clâ/CHâOH/Oâ system. The spectrum shows a strong maximum at 207 nm, with Ï = 9.5 à 10â»Â¹â¸ cm² moleculeâ»Â¹ and a weak maximum near 245 nm with Ï = 3.7 à 10â»Â¹â¸ cm² moleculeâ»Â¹. Kinetic data were obtained at 600 Torr of air over the temperature range 253-368 K. Rate constants were deduced from computer simulations of the absorption traces obtained at various wavelengths using nonlinear least-squares treatment of multiple time profiles. The following reactions were studied: 2CHâCOOâ â 2CHâCOO + Oâ (4); CHâCOOâ + CHâOâ â CHâCOO + CHâO + Oâ (3a); CHâCOOâ + CHâOâ â CHâCOOH + HCHO + Oâ (3b); the rate constants can be expressed in Arrhenius form as follows: kâ = 2.8 à 10â»Â¹Â² exp((530 {plus minus} 100)/T); k{sub 3a} = 1.8 à 10â»â¹ exp(-(1800 {plus minus} 1100)/T); k{sub 3b} = 4.1 à 10â»Â¹âµ exp((2100 {plus minus} 1200)/T), all in units of cm³ moleculeâ»Â¹ sâ»Â¹, the errors being 2 standard deviations. These expressions are valid only at tropospheric temperatures, and a global value of kâ, independent of the temperature, is kâ = (1.4 {plus minus} 0.3) à 10â»Â¹Â¹ cm³ moleculeâ»Â¹ sâ»Â¹.
Journal of the Chemical Society, Faraday Transactions 2, 1989
... Geert K. Moortgat,* Richard A. Cox,? ... Barnes et all9 observed an overall slow effective de... more ... Geert K. Moortgat,* Richard A. Cox,? ... Barnes et all9 observed an overall slow effective decay of H02 in the presence of CH,CHO; kefl = 1 x In the present study we report the determination of the final products by long-path Ftir spectroscopy as a function of various initial CH3CH0 ...
The Journal of Physical Chemistry A
ABSTRACT
The Journal of Organic Chemistry, 2011
Dilute mixtures of n-octanal in synthetic air (up to 100 ppm) were photolyzed with fluorescent UV... more Dilute mixtures of n-octanal in synthetic air (up to 100 ppm) were photolyzed with fluorescent UV lamps (275-380 nm) at 298 K. The main photooxidation products were 1-hexene, CO, vinyl alcohol, and acetaldehyde. The photolysis rates and the absolute quantum yields were found to be slightly dependent on the total pressure. At 100 Torr, Φ(100) = 0.41 ± 0.06, whereas at 700 Torr the total quantum yield was Φ(700) = 0.32 ± 0.02. Two decomposition channels were identified: the radical channel C(7)H(15)CHO → C(7)H(15) + HCO and the molecular channel C(7)H(15)CHO → C(6)H(12) + CH(2)═CHOH, having absolute quantum yields of 0.022 and 0.108 at 700 Torr. The product CH(2)═CHOH tautomerizes to acetaldehyde. Carbon balance data lower than unities suggest the existence of unidentified decomposition channel(s) which substantially contributes to the photolysis. On the basis of experimental and theoretical evidence, n-octanal photolysis predominantly proceeds to form Norrish type II products as the major ones.
The Journal of Physical Chemistry A, 2012
Dilute mixtures of n-butanal, 3-methylbutanal, and 3,3-dimethylbutanal in synthetic air, differen... more Dilute mixtures of n-butanal, 3-methylbutanal, and 3,3-dimethylbutanal in synthetic air, different N(2)/O(2) mixtures, and pure nitrogen (up to 100 ppm) were photolyzed with fluorescent UV lamps (275-380 nm) at 298 K. The main photooxidation products were ethene (n-butanal), propene (3-methylbutanal) or i-butene (3,3-dimethylbutanal), CO, vinylalcohol, and ethanal. The photolysis rates and the absolute quantum yields were found to be dependent on the total pressure of synthetic air but not of nitrogen. At 100 Torr, the total quantum yield Φ(100) = 0.45 ± 0.01 and 0.49 ± 0.07, whereas at 700 Torr, Φ(700) = 0.31 ± 0.01 and 0.36 ± 0.03 for 3-methylbutanal and 3,3-dimethybutanal, respectively. Quantum yield values for n-butanal were reported earlier by Tadić et al. (J. Photochem. Photobiol. A2001143, 169-179) to be Φ(100) = 0.48 ± 0.02 and Φ(700) = 0.32 ± 0.01. Two decomposition channels were identified: the radical channel RCHO → R + HCO (Norrish type I) and the molecular channel CH(3)...
Fine mode aerosol was collected on quartz fiber filters at several sites across Europe. These sam... more Fine mode aerosol was collected on quartz fiber filters at several sites across Europe. These samples were analyzed for carboxylic acids by liquid chromatography coupled to a hybrid (quadrupole and time-of-flight) mass spectrometer (LC/ MS/MS-TOF). A series of oxodicarboxylic acids (C 7 -C 11 ) was detected. Oxodicarboxylic acids are linear dicarboxylic acids with an additional carbonyl group. Previous measurements of these acids are scarce and their sources are largely unknown. Several structural isomers (different positions of the carbonyl group within the molecule) could be identified and differentiated by the combination of laboratory experiments and high mass accuracy measurements. The homologs with 9-11 carbon atoms were identified for the first time in atmospheric aerosol particles. The concentrations of oxodicarboxylic acids in ambient aerosol samples frequently exceeded those of the corresponding unsubstituted dicarboxylic acids. Oxodicarboxylic acids have been shown to be products of the reaction of dicarboxylic acids with OH radicals in chamber experiments and a reaction mechanism is proposed. Good correlation of oxodicarboxylic acid and hydroxyl radical concentrations was found at two measurement sites (Finland and Crete) of different geographic location and meteorological conditions. The ratios of individual isomers from the field samples are comparable to those of the laboratory experiments. The results of this study imply that the reaction of OH radicals and dicarboxylic acids is an important pathway for the production of oxodicarboxylic acids in the atmosphere. Oxodicarboxylic acids seem to be important intermediates in atmospheric oxidation processes of organic compounds. r
4-Oxopentanoic acid was characterized experimentally by electrospray ionization using a triple qu... more 4-Oxopentanoic acid was characterized experimentally by electrospray ionization using a triple quadrupole and time-of-flight analyzer hybrid system. This compound was chosen as a model substance for small organic compounds bearing an acetyl and a carboxyl group. Collision-induced dissociation experiments at different activation energies were performed to elucidate possible fragmentation pathways. These pathways were also studied on the theoretical level using density functional theory (DFT) B3LYP/6-311++G(3df,3pd)//B3LYP/6-31+G(d)+ZPVE calculations. CO2 ejection from the [M-H](-) anion of 4-oxopentanoic acid was observed and the fragmentation pathway studied by DFT reveals a new concerted mechanism for CO2 elimination accompanied by an intramolecular proton transfer within a pentagonal transition state structure. Successive elimination of water and CO from the [M-H](-) anion of 4-oxopentanoic acid was also observed. A rearrangement in the primary deprotonated ketene anion produced after water elimination was found on the theoretical level and leads to CO elimination from the primary product anion [M-H-H2O](-). Energy diagrams along the reaction coordinates of the fragmentation pathways are presented and discussed in detail. Mulliken charge distributions of some important structures are presented.
The objective of this work was to develop a method to determine the concentrations of higher orga... more The objective of this work was to develop a method to determine the concentrations of higher organic acids in snow samples. The target species are the homologous aliphatic α,ω-dicarboxylic acids from C 5 to C 13 , pinonic acid, pinic acid and phthalic acid. A preconcentration procedure utilizing solid phase extraction was developed and optimized using solutions of authentic standards. The influences of different parameters such as flow rate during extraction and the concentration of the eluent on the efficiency of the extraction procedure were investigated. The compounds of interest were separated by HPLC and detected by a quadrupole time-of-flight mass spectrometer (qTOF-MS). The recovery rate (extraction efficiency) of the extraction procedure was found to vary between 41% for tridecanedioic acid and 102% for adipic acid. The limits of detection were determined for all compounds and were between 0.9 nmol/L (dodecanedioic acid) and 29.5 nmol/L (pinonic acid). An exception is pinic acid, for which a considerably higher detection limit of 103.9 nmol/L was calculated. Snow samples were collected in December 2006 and January 2007 at the Fee glacier (Switzerland) from locations at heights from 3056 to 3580 m asl and from different depths within the snow layer. In total, the analysis of 61 single snow samples was performed, and the following compounds could be quantified: homologous aliphatic α,ωdicarboxylic acids with 5-12 carbon atoms and phthalic acid. Tridecanedioic acid, pinonic and pinic acid were identified in the samples but were not quantified due to their low concentrations. The three most abundant acids found in the molten snow samples were glutaric acid (C 5 -di; 3.90 nmol/L), adipic acid (C 6 -di; 3.35 nmol/L) and phthalic acid (Ph; 3.04 nmol/L).
The temperature dependence of secondary organic aerosol (SOA) formation from ozonolysis of β-pine... more The temperature dependence of secondary organic aerosol (SOA) formation from ozonolysis of β-pinene was studied in a flow reactor at 263 K-303 K and 1007 hPa under dry and humid conditions (0% and 26%-68% relative humidity, respectively). The observed SOA yields reached maximum values of 0.18-0.39 at high particle mass concentrations (M o ). Under dry conditions, the measurement data showed an overall increase in SOA yield with inverse temperature, but significant oscillatory deviations from the predicted linear increase with inverse temperature (up to 50% at high M o ) was observed. Under humid conditions the SOA yield exhibited a linear decrease with inverse temperature. For the atmospherically relevant concentration level of M o =10 µg m −3 and temperature range 263 K-293 K, the results from humid experiments in this study indicate that the SOA yield of β-pinene ozonolysis may be well represented by an average value of 0.15 with an uncertainty estimate of ±0.05. When fitting the measurement data with a twoproduct model, both the partitioning coefficients (K om,i ) and the stoichiometric yields (α i ) of the low-volatile and semivolatile model species were found to vary with temperature. The results indicate that not only the reaction product vapour pressures but also the relative contributions of different gasphase or multiphase reaction channels are strongly dependent on temperature and the presence of water vapour. In fact, the oscillatory positive temperature dependence observed under dry conditions and the negative temperature dependence observed under humid conditions indicate that the SOA yield is governed much more by the temperature and humidity dependence of the involved chemical reactions than by vapour
The temperature dependence of secondary organic aerosol (SOA) formation from ozonolysis of β-pine... more The temperature dependence of secondary organic aerosol (SOA) formation from ozonolysis of β-pinene was studied in a flow reactor at 263-303 K and 1007 hPa. The observed SOA yields were of similar magnitude as predicted by a two-product model based on detailed gas phase chemistry , reaching maximum values of 5 0.22-0.39 at high particle mass concentrations. However, the measurement data exhibited significant deviations (up to 50%) from the predicted linear dependence on inverse temperature. When fitting the measurement data with a two-product model, we found that both the partitioning coefficients (K om,i ) and the stoichiometric yields (α i ) of the low-volatile and semi-volatile species vary with temperature. The results indicate 10 that not only the reaction product vapour pressures but also the relative contributions of different gas-phase or multiphase reaction channels are dependent on temperature. We suggest that the modelling of secondary organic aerosol formation in the atmosphere needs to take into account the effects of temperature on the pathways and kinetics of the involved chemical reactions as well as on the gas-particle partitioning of 15 the reaction products. 20 vegetation emit large amounts of biogenic volatile organic compounds (BVOCs) (500-1800 Tg C yr −1 ). Besides isoprene monoterpenes are the most abundant BVOCs, and with an emission rate of 10-50 Tg C yr −1 β-pinene is the second most important monoterpene (Wiedinmyer et al., 2004). Biogenic secondary organic aerosol (SOA) are formed from oxidation of BVOCs in the atmosphere by O 3 , OH and NO 3 radicals, Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Printer-friendly Version Interactive Discussion
The Journal of Physical Chemistry, 1989
The ultraviolet absorption spectrum of the acetylperoxy radical was measured in the range 190-280... more The ultraviolet absorption spectrum of the acetylperoxy radical was measured in the range 190-280 nm. The radical was generated by flash photolysis of Clâ/CHâCHO/Oâ mixtures. The absorption spectrum was calibrated against the HOâ radical generated in the Clâ/CHâOH/Oâ system. The spectrum shows a strong maximum at 207 nm, with Ï = 9.5 à 10â»Â¹â¸ cm² moleculeâ»Â¹ and a weak maximum near 245 nm with Ï = 3.7 à 10â»Â¹â¸ cm² moleculeâ»Â¹. Kinetic data were obtained at 600 Torr of air over the temperature range 253-368 K. Rate constants were deduced from computer simulations of the absorption traces obtained at various wavelengths using nonlinear least-squares treatment of multiple time profiles. The following reactions were studied: 2CHâCOOâ â 2CHâCOO + Oâ (4); CHâCOOâ + CHâOâ â CHâCOO + CHâO + Oâ (3a); CHâCOOâ + CHâOâ â CHâCOOH + HCHO + Oâ (3b); the rate constants can be expressed in Arrhenius form as follows: kâ = 2.8 à 10â»Â¹Â² exp((530 {plus minus} 100)/T); k{sub 3a} = 1.8 à 10â»â¹ exp(-(1800 {plus minus} 1100)/T); k{sub 3b} = 4.1 à 10â»Â¹âµ exp((2100 {plus minus} 1200)/T), all in units of cm³ moleculeâ»Â¹ sâ»Â¹, the errors being 2 standard deviations. These expressions are valid only at tropospheric temperatures, and a global value of kâ, independent of the temperature, is kâ = (1.4 {plus minus} 0.3) à 10â»Â¹Â¹ cm³ moleculeâ»Â¹ sâ»Â¹.
Journal of the Chemical Society, Faraday Transactions 2, 1989
... Geert K. Moortgat,* Richard A. Cox,? ... Barnes et all9 observed an overall slow effective de... more ... Geert K. Moortgat,* Richard A. Cox,? ... Barnes et all9 observed an overall slow effective decay of H02 in the presence of CH,CHO; kefl = 1 x In the present study we report the determination of the final products by long-path Ftir spectroscopy as a function of various initial CH3CH0 ...
The Journal of Physical Chemistry A
ABSTRACT