Electron Impact Ionization Mass Research Articles

Improved Discrimination of Mass Spectral Isomers Using the High-Dimensional Consensus Mass Spectral Similarity Algorithm.

This study employs a high-dimensional consensus mass spectral (HDCMS) similarity scoring technique to discriminate isomers collected using an electron ionization mass spectrometer. The HDCMS method was previously introduced and applied to the discrimination of mass spectra of constitutional isomers, methamphetamine and phentermine, collected with direct analysis real-time mass spectrometry (DART-MS). The method formulates the problem of discriminating mass spectra in a mathematical Hilbert space and is hence called "high dimensional." It requires replicate mass spectra to build a Gaussian model and evaluate the inner products between these functions. The resulting measurement variability is used as a signature by which to discriminate spectra. In this work, HDCMS is tested on electron impact ionization (EI) mass spectra of 7 terpene and terpene-related (C10H16 and C10H14) isomers with experimental retention indices that differ by less than 30 and with traditional cosine similarity scores greater than 0.9, on a scale of 0 to 1, when compared with at least one other compound in the test set. Using identical instrument parameters, 15 replicate gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) spectra of each isomer were collected and separated into distinct library and query sets. The HDCMS algorithm discriminated each isomer, indicating the method's potential. Because the method requires replicate measurements, observations from a simple heuristic study of the number of replicates required to discriminate these isomers is presented. The paper concludes with a discussion of compound discrimination using HDCMS and the benefits and drawbacks of applying the method to EI-MS data.

Self-reducing precursors for aluminium metal thin films: evaluation of stable aluminium hydrides for vapor phase aluminium deposition.

Thin films of Al as interconnect materials and those of AlN as wide bandgap semiconductor and piezoelectric material are of great interest for microelectronic applications. For the fabrication of these thin films via chemical vapor deposition (CVD) based routes, the available precursor library is rather limited, mostly comprising aluminium alkyls, chlorides, and few small amine-stabilized aluminium hydrides. Herein, we focused on rational precursor development for Al, their characterization and comparison to existing precursors comprising stabilized aluminium hydrides. We present and compare a series of potentially new and reported aluminium hydride precursors divided into three main groups with respect to their stabilization motive, and their systematic structural variation to evaluate the physicochemical properties. All compounds were comprehensively characterized by means of nuclear magnetic resonance spectroscopy (NMR), Fourier-transform infrared spectroscopy (FTIR), elemental analysis (EA), electron-impact ionization mass spectrometry (EI-MS) and thermogravimetric analysis (TGA). Promising representatives were further evaluated as potential single source precursors for aluminium metal formation in proof-of-concept experiments. Structure and reaction enthalpies with NH3 or H2 as co-reactants were calculated via first principles density functional theory simulations and show the great potential as atomic layer deposition (ALD) precursors for Al and AlN thin films.

Crannenols A-D, Sesquiterpenoids from the Irish Deep-Sea Soft Coral Acanella arbuscula.

Four undescribed sesquiterpenoids, crannenols A-D (1-4), have been isolated from CHCl2 and MeOH extracts of the deep-sea bamboo coral Acanella arbuscula. The corals were collected from a submarine canyon on the edge of Ireland's Porcupine Bank via a remotely operated vehicle. The structure elucidation of these (Z,E)-α-farnesene derivatives was achieved using a combination of 1D and 2D NMR, electron impact (1, 2), and electrospray ionization (3, 4) mass spectrometry.

Utility of gas chromatography infrared spectroscopy (GC-IR) for the differentiation of positional isomers of fentanyl related substances

Forensic laboratories routinely use gas chromatography mass spectrometry (GC–MS) in the identification of controlled substances using both retention time and electron impact ionization (EI) mass spectra. Certain drugs such as positional isomers of some fentanyl related substances (FRS) can produce indistinguishable EI mass spectra but may be differentiated using retention time. The core structure of fentanyl consists of an amide group, a piperidine ring, an aniline ring, and an N-alkyl chain, each providing opportunities for points of substitution that create FRS and corresponding positional isomers. For this study, the analysis by GC coupled to a vapor-phase infrared spectroscopy detector (GC-IR) was used as a complementary technique to GC–MS for the identification of positional isomers of FRS. The result is a novel fentanyl library consisting of 212 different FRS reference compounds. A collaboration among three different laboratories yielded correct identifications of twenty blind samples when searched against the GC-IR FRS library created at Florida International University (FIU). The expected limits of detection for fentanyl using GC-IR range between 0.10 and 0.19 mg/mL, depending on the sample introduction (injector) method and other instrumental parameters. The newly created GC-IR library and its GC–MS counterpart of 212 FRS are shared in the supplementary materials for future use by researchers and practitioners.

Blue-green light is required for a maximized fatty acid unsaturation and pigment concentration in the microalga Acutodesmus obliquus.

Blue-green light is known to maximize the degree of fatty acid (FA) unsaturation in microalgae. However, knowledge on the particular waveband responsible for this stimulation of FA desaturation and its impact on the pigment composition in microalgae remains limited. In this study, Acutodesmus obliquus was cultivated for 96 h at 15°C with different light spectra (380-700 nm, 470-700 nm, 520-700 nm, 600-700 nm, and dark controls). Growth was monitored daily, and qualitative characterization of the microalgal FA composition was achieved via gas chromatography coupled with electron impact ionization mass spectrometry (GC-EI/MS). Additionally, a quantitative analysis of microalgal pigments was performed using high-performance liquid chromatography with diode array detection (HPLC-DAD). Spectra that included wavelengths between 470 and 520 nm led to a significantly higher percentage of the polyunsaturated fatty acids (PUFA) 18:3 and 16:4, compared to all other light conditions. However, no significant differences between the red light cultivations and the heterotrophic dark controls were observed for the FA 18:3 and 16:4. These results indicate, that exclusively the blue-green light waveband between 470 and 520 nm is responsible for a maximized FA unsaturation in A. obliquus. Furthermore, the growth and production of pigments were impaired if blue-green light (380-520 nm) was absent in the light spectrum. This knowledge can contribute to achieving a suitable microalgal pigment and FA composition for industrial purposes and must be considered in spectrally selective microalgae cultivation systems.

Electron Impact Ionization Mass Spectra of 3-Amino 6-Chloro2-methyl Quinazolin-4-(3H)-one Derivative

Looking at the previous studies on quinazolinones derivatives, only limited information’s are available on their mass spectral along with the preparation of novel quinazolin-4-(3H)-one derivatives The condensation of Methyl-2-amino-4-Chlorobenzoate with acetic anhydride yielded the cyclic compound 2-methyl 7-Chloro-1, 3-benzo-oxazine-4-one (1) which further produce 3-Amino-2-Methyl 7-Chloro quinazolin-4(3H)-ones (2) via the reaction with hydrazine hydrate. The compounds synthesized were unequivocally confirmed by means of Infrared, Nuclear Magnetic Resonance (1H and 13C), Gas Chromatography-Mass spectrophotometry and Elemental analysis. Discussion: The molecular ion of m/z 235 fragments to give m/z 220 by loss of –NH group. The ion of m/z 220 was broken to give m/z 206 by losing CH2 group and fragment to m/z 177 by loss of HCO. This fragmented to m/z 162 by loss of –CH3 group and then m/z 136 by loss of CN group. The loss of O gave m/z 120 which fragment to give m/z 93 by loss of –HCN and finally gave m/z 65 by loss of CO group. Conclusion: The electron impact ionization mass spectra of compound 2show a weak molecular ion peak and a base peak of m/z 235resulting from a cleavage fragmentation. Compound 2 give a characteristic fragmentation pattern. From the study of the mass spectra of compound 2, it was found that the molecular ion had fragmented to the m/z 220. The final fragmentation led to ion of m/z 93 and ion of mass m/z 65, respectively

Growth and fatty acid composition of Acutodesmus obliquus under different light spectra and temperatures.

The combined impact of temperature and light spectra on the fatty acid (FA) composition in microalgae has been sparsely investigated. The aim of this study was to investigate the interactions of light and temperature on the FA composition in Acutodesmus obliquus. For this purpose, A. obliquus was cultivated with different temperatures (20, 30, and 35°C), as well as broad light spectra (blue, green, and red light). Growth and FA composition were monitored daily. Microalgal FA were extracted, and a qualitative characterization was done by gas chromatography coupled with electron impact ionization mass spectrometry (GC-EI/MS). Compared to red light, green and blue light caused a higher percentage of the polyunsaturated fatty acids (PUFA) 16:4, 18:3, and 18:4, at all temperatures. The highest total percentage of these PUFA were observed at the lowest cultivation temperature and blue and green light. These data imply that a combination of lower temperatures and blue-green light (450-550 nm) positively influences the activity of specific FA-desaturases in A. obliquus. Additionally, a lower 16:1 trans/cis ratio was observed upon green and blue light treatment and lower cultivation temperatures. Remarkably, green light treatment resulted in a comparably high growth under all tested conditions. Therefore, a higher content of green light, compared to blue light might additionally lead to a higher biomass concentration. Microalgae cultivation with low temperatures and green light might therefore result in a suitable FA composition for the food industry and a comparably high biomass production.

Modification of the Lipid Profile of the Initial Oral Biofilm In Situ Using Linseed Oil as Mouthwash.

Lipids are of interest for the targeted modification of oral bioadhesion processes. Therefore, the sustainable effects of linseed oil on the composition and ultrastructure of the in situ pellicle were investigated. Unlike saliva, linseed oil contains linolenic acid (18:3), which served as a marker for lipid accumulation. Individual splints with bovine enamel slabs were worn by five subjects. After 1 min of pellicle formation, rinses were performed with linseed oil for 10 min, and the slabs’ oral exposure was continued for up to 2 or 8 h. Gas chromatography coupled with electron impact ionization mass spectrometry (GC-EI/MS) was used to characterize the fatty acid composition of the pellicle samples. Transmission electron microscopy was performed to analyze the ultrastructure. Extensive accumulation of linolenic acid was recorded in the samples of all subjects 2 h after the rinse and considerable amounts persisted after 8 h. The ultrastructure of the 2 h pellicle was less electron-dense and contained lipid vesicles when compared with controls. After 8 h, no apparent ultrastructural effects were visible. Linolenic acid is an excellent marker for the investigation of fatty acid accumulation in the pellicle. New preventive strategies could benefit from the accumulation of lipid components in the pellicle.

Structural effect on electron impact decomposition of 1,3- and 1,4-cyclohexane dinitrites

Alkyl dinitrites have attracted attention as an important type of nitrosating agent and a pollution source in atmosphere. The reactivity and chemistry of alkyl dinitrites induced by the two ONO functional groups are relatively unknown. In this work, decompositions of 1,3- cyclohexane dinitrite and 1,4-cyclohexane dinitrite are studied by electron impact ionization mass spectroscopy (EI-MS). Apart from NO+ (m/z=30), fragment ions m/z=43 and 71 are the most abundant for the 1,3-isomer. On the other hand, fragments m/z=29, 57, 85, and 97 stand out in the EI-MS spectrum of 1,4-isomer. Possible dissociation mechanisms of the two dinitrites are proposed by theoretical calculations. The results reveal that the ring-opening of 1,3-cyclohexane dinitrite mainly starts from the intermediate ion (M-NO)+ by cleavage of two αC-βC bonds. For 1,4-cyclohexane dinitrite, in addition to the decomposition via intermediate (M-NO)+, cleavage of βC-βC bonds can occur directly from the parent cation M+. The results will help to understand the structural related chemistry of alkyl dinitrites in atmosphere and in NO transfer process.

Electron Impact Ionization Mass Spectra of 3-Amino 6-Chloro-2-methyl Quinazolin-4-(3H)-one Derivative

Background: Looking at the previous studies on quinazolinones derivatives, only limited information’sare available on their massspectral along with the preparation of novel quinazolin-4-(3H)-one derivatives. Consolidation of Methyl-2-amino-4-Chlorobenzoate with acetic anhydride produced the cyclic compound 2-methyl 7-Chloro-1, 3-benzo-oxazine-4-one (1) which then produced 3-Amino-2-Methyl 7-Chloro quinazolin-4(3H)-ones (2) through the reaction with hydrazine hydrate. These compounds synthesized were indisputably confirmed by means of Infrared, Nuclear Magnetic Resonance (¹H and ¹³C), Gas Chromatography-Mass spectrophotometry and Elemental analysis. Discussion: The molecular ion of m/z 235 fragments to give m/z 220 by loss of –NH group. The ion of m/z 220 was broken to give m/z 206 by losing CH₂ group and fragment to m/z 177 by loss of HCO. This fragmented to m/z 162 by loss of –CH₃ group and then m/z 136 by loss of CN group. The loss of O gave m/z 120 which fragment to give m/z 93 by loss of –HCN and finally gave m/z 65 by loss of CO group. Conclusion: The electron impact ionization mass spectra of compound 2 show a weak molecular ion peak and a base peak of m/z 235 resulting from a cleavage fragmentation. Compound 2 give a characteristic fragmentation pattern. From the study of the mass spectra of compound 2, it was found that the molecular ion had fragmented to the m/z 220. The final fragmentation led to ion of m/z 93 and ion of mass m/z 65, respectively.

Time-Resolved Quantification of Phenolic Antioxidants and Oxidation Products in a Model Fuel by GC-EI-MS/MS

Phenol-type components, such as butylated hydroxytoluene (BHT), are used as antioxidants (AOs) to enhance the thermo-oxidative stability of kerosene-type Jet A-1 fuel. Although the antioxidative effect of BHT is well known and often published, there is far less information about the degradation products of BHT in fuels and their impact on stability toward oxidation. In order to monitor a time-resolved depletion of BHT in model kerosene, an artificial alteration method adapted for regular sampling was applied. Subsequently, the molecular structure of degradation products of BHT was identified by gas chromatography with electron impact ionization mass spectrometry (GC-EI-MS). For the quantification of the residual BHT as well as the two representatives of degradation products, namely, 3,5-di-tert-butyl-4-hydroxybenzaldehyde (HBA) and 2,6-di-tert-butyl-p-benzoquinone (BQ), an analytical technique comprising a GC-EI triple quadrupole mass spectrometer run in the MS/MS mode was developed. The limit of detection (LOD) and the limit of quantification (LOQ) for BHT, BQ, and HBA were determined below 1 ppb. The formation of BQ and HBA was observed shortly after the nascent degradation of BHT, while an increase of oxidation products derived from the fuel ascended remarkably after a full depletion of both the initial AO BHT and the monitored oxidation products BQ and HBA. As the evolution of BQ and HBA followed a characteristic trend, these compounds can be used as markers to reliably predict the residual time until a total consumption or a predefined threshold of BHT is reached. This way, the quality management of in-service or stored kerosene-type fuels is enhanced.

Mass Spectra of New Heterocycles: XX. Electron Impact and Chemical Ionization Mass Spectra of 5-(Prop-2-yn-1-ylsulfanyl)-1H-pyrrol-2-amines

Electron impact (70 eV) and chemical ionization (methane as reactant gas) mass spectra of 1-alkyl- and 1-[2-(vinyloxy)ethyl]-5-(prop-2-yn-1-ylsulfanyl)-1H-pyrrol-2-amines have been studied for the first time. The title compounds under electron impact form stable molecular ions which decompose mainly along pathways typical of the molecular ions derived from the corresponding intramolecular cyclization products, 7-alkyl- and 7-[2-(vinyloxy)ethyl]-2,7-dihydrothiopyrano[2,3-b]pyrrol-6-amines. In addition, fragment ions that could be formed only via decomposition of unrearranged molecular ion were detected. The main fragmentation pathway of their molecular ions involves cleavage of the N1-CAlk bond with the formation of stable [M − R3]+ ions (Irel 85–100%) {except for N,N-diethyl- and N,N-dipropyl-1-[2-(vinyloxy)emyl]-5-(prop-2-yn-1-ylsulfanyl)-1H-pyrrol-2-amines}. The results of quantum chemical calculations at the B3LYP/6-311+G(d,p) level of theory are consistent with the experimental data. In the chemical ionization mass spectra of 5-(prop-2-yn-1-ylsulfanyl)-1H-pyrrol-2-amines, the major peaks were those corresponding to M+· (Irel 65–100%) and [M + H]+ (Irel 75–100%). The title compounds have been found to undergo partial (5–10%) thermally induced isomerization to 5-(prop-1-yn-1-ylsulfanyl)-1H-pyrrol-2-amines under the chemical ionization conditions.

Ammonium Salts as a Source of Small Molecules Observed with High-Resolution Electron-Impact Ionization Mass Spectrometry.

Recent high-resolution in situ mass spectrometry at comet 67P/Churyumov-Gerasimenko visited by European Space Agency's Rosetta spacecraft raised the question, if sublimating ammonium salts can unequivocally be detected in the cometary coma. In laboratory experiments with the twin model of the space instrument, two prototypic ammonium salts NH4B, namely, ammonium chloride (B = Cl-) and ammonium formate (B = HCOO-) (as well as methodologically relevant isotopologues), were allowed to sublimate in vacuum while mass spectra were collected. High-resolution electron-impact ionization mass spectrometry provides an outstanding experimental tool to investigate the complex physicochemical processes occurring during the sublimation of ammonium salts. Sublimation of ammonium chloride led to the observation of the ammonium cation NH4+ and the chloramide molecule NH2Cl in the neutral gas mode of the instrument. These observations could be jointly interpreted as indirect evidence for the existence of a neutral gaseous parent species (either as the molecular complex NH3···HB or the double-ionic species NH4+···B-). However, the qualitative fragmentation pattern we present for 13C15N-ammonium formate suggests an alternative route of NH4+ production within the ionization region of the instrument, namely, by protonation/hydrogenation. Besides NH4+, other species were observed that were formed in protonation/hydrogenation reactions. Moreover, together with the two major species from the decomposition of the salt, ammonia and formic acid, three minor species also contributed to the fragmentation pattern: HCN/HNC, HOCN/HNCO, and CH3NO. Like chloramide, formamide (CH3NO) also is a secondary species probably formed in a pseudo-intramolecular chemical reaction while ammonia and the respective acid are in a state of association. HCN/HNC and HOCN/HNCO are ternary products coming out of formamide decomposition reactions. We discuss our experimental findings, summarized in a tentative chemical reaction network, in light of the available theoretical literature and highlight their relevance for the interpretation of in situ measurements in space research.

Mass Spectra of New Heterocycles: XVIII. Electron Impact and Chemical Ionization Mass Spectra of Alkyl 5-Amino-3-methyl-4-(1H-pyrrol-1-yl)thiophene-2-carboxylates

Electron impact (70 eV) and chemical ionization (methane as reactant gas) mass spectra of alkyl 5-amino-3-methyl-4-(1H-pyrrol-1-yl)thiophene-2-carboxylates have been studied for the first time. All compounds, except for tert-butyl thiophene-2-carboxylate, under electron impact give rise to stable molecular ions which decompose along two paths, depending on the site of positive charge localization (at the ester fragment or amino nitrogen atom). The main fragmentation pathway of the molecular ions is elimination of alkoxy radical from the ester group. Chemical ionization of alkyl 5-amino-3-methyl-4-(1H-pyrrol-1-yl)-thiophene-2-carboxylates involves protonation and electrophilic addition with the base peak corresponding to the [M + H]+ ion.

Kinetic study of the F2 + C2H4 reaction: Disagreement between theory and experiment resolved?

Abstract Reaction F2 + C2H4 → F + C2H3F (1) has been studied using a discharge flow reactor combined with an electron impact ionization mass spectrometer. The reaction rate constant was determined either from kinetics of the reaction product, F-atom, formation or from the kinetics of F2 consumption in excess of C2H4: k1 = (7.94 ± 2.06) × 10−12 exp(−(3867 ± 120)/T) cm3 molecule−1 s−1 at T = 297–833 K. The reaction activation energy, 7.7 ± 0.3 kcal mol−1, is consistent with current theoretical prediction for the reaction barrier height and seems to solve the long-standing problem of the divergence between theory and experiment.

Electron Impact Ionization Mass Spectra of 3-Amino 5,6-Dimethoxyl-2-Methyl Quinazolin-4-(3H)-One Derivative

Background: The synthesis of novel heterocyclic derivatives has attracted considerable attention. The explosive growth of heterocyclic chemistry is emphasized by the large number of research publications, monographs, and reviews. The heterocyclic organic compounds are extensively disseminated in natural and synthetic medicinal chemistry and are vital for human life. Looking at the previous studies on quinazolinones derivatives, only limited informationis available on their mass spectral along with the preparation of novel quinazolin-4-(3H)-one derivatives. Objective: Objective of this study, was to synthesize a novel 2-Methyl-6, 7-dimethoxy-quinazolin-4-one was synthesized via the reaction between 2-Methyl-6, 7-dimethoxy-benzo-1,3-oxazin-4-one andhydrazine hydrate and study their electron impact ( EI ) mass spectral fragmentation. Method: The condensation of 2-amino-methyl-4, 5-dimethoxybenzoate with acetic anhydride yielded the cyclic compound 2-methyl-4, 5-disubstituted-1, 3-benzo-oxazine-4-one which further produce a novel 2,3-disubstituted quinazolin-4 ones via the reaction with hydrazine hydrate. The compounds synthesized were unequivocally confirmed by means of Infrared, Nuclear Magnetic Resonance (1H and 13C), Gas Chromatography Mass Spectrophotometer and Elemental analysis. Discussion: The molecular ion of m/z 235 fragment to give m/z 220 by loss of –NH group. The ion of m/z 220 was broken to give m/z 206 by losing CH2 group and fragment to m/z 177 by loss of HCO. This fragmented to m/z 162 by loss of –CH3 group and then m/z 136 by loss of CN group. The loss of O gave m/z 120 which fragment to give m/z 93 by loss of –HCN and finally gave m/z 65 by loss of CO group. Conclusion: The electron impact ionization mass spectra of compound 2show a weakmolecular ion peak and a base peak ofm/z 235resulting from a cleavage fragmentation. Compound 2 give a characteristic fragmentation pattern. From the study of the mass spectra of compound 2, it was found that the molecular ion had fragmented to the m/z 220. The final fragmentation led to ion of m/z 93 and ion of mass m/z 65, respectively.

Liquid Extraction Surface Analysis (LESA) Electron-Induced Dissociation and Collision-Induced Dissociation Mass Spectrometry of Small Molecule Drug Compounds

Here, we present liquid extraction surface analysis (LESA) coupled with electron-induced dissociation (EID) mass spectrometry in a Fourier-transform ion cyclotron resonance mass spectrometer for the analysis of small organic pharmaceutical compounds directly from dosed tissue. First, the direct infusion electrospray ionisation EID and collision-induced dissociation (CID) behaviour of erlotinib, moxifloxacin, clozapine and olanzapine standards were compared. EID mass spectra were also compared with experimental or reference electron impact ionisation mass spectra. The results show that (with the exception of erlotinib) EID and CID result in complementary fragment ions. Subsequently, we performed LESA EID MS/MS and LESA CID MS/MS on singly charged ions of moxifloxacin and erlotinib extracted from a thin tissue section of rat kidney from a cassette-dosed animal. Both techniques provided structural information, with the majority of peaks observed for the drug standards also observed for the tissue-extracted species. Overall, these results demonstrate the feasibility of LESA EID MS/MS of drug compounds from dosed tissue and extend the number of molecular structures for which EID behaviour has been determined.Graphical ᅟ

Kinetics and Products of the Reactions of F2 with Br‐Atom and Br2

ABSTRACTReactions of F2 molecules exhibit unusual features, manifesting in high reactivity of F2 with respect to some closed‐shell molecules and low reactivity toward chemically active species, such as halogen and oxygen atoms. The existing data base on the reactions of F2 being rather sparse, kinetic and mechanistic studies (preferably over a wide temperature range) are needed to better understand the nature of the specific reactivity of fluorine molecule. In the present work, reactions of F2 with Br atoms and Br2 have been studied for the first time in an extended temperature range using a discharge flow reactor combined with an electron impact ionization mass spectrometer. The rate constant of the reaction F2 + Br → F +BrF (1) was determined either from kinetics of the reaction product, BrF, formation or from the kinetics of Br consumption in excess of F2: k1 = (4.66 ± 0.93) × 10−11 exp(−(4584 ± 86)/T) cm3 molecule−1 s−1 at T = 300–940 K. The rate constant of the reaction F2 + Br2 → products (2), k2 = (9.23 ± 2.68) × 10−11 exp(−(8373 ± 194)/T) cm3 molecule−1 s−1, was determined in the temperature range 500–958 K by monitoring both reaction product (FBr) formation and F2 consumption kinetics in excess of Br2. The results of the experimental measurements of the yield of FBr (1.02 ± 0.07 at T = 960 K) combined with thermochemical calculations indicate that F+Br2F forming channel of reaction (2) is probably the dominant one, at least, at highest temperature of the study.

Reaction F + C2H4: Rate Constant and Yields of the Reaction Products as a Function of Temperature over 298-950 K.

The kinetics and products of the reaction of F + C2H4 have been studied in a discharge flow reactor combined with an electron impact ionization mass spectrometer at nearly 2 Torr total pressure of helium in the temperature range 298-950 K. The total rate constant of the reaction, k1 = (1.78 ± 0.30) × 10-10 cm3 molecule-1 s-1, determined under pseudo-first-order conditions, monitoring the kinetics of F atom consumption in excess of C2H4, was found to be temperature independent in the temperature range used. H, C2H3F, and HF were identified as the reaction products. Absolute measurements of the yields of these species allowed to determine the branching ratios, k1b/ k1 = (0.73 ± 0.07) exp(-(425 ± 45)/ T) and k1a/ k1 = 1 - (0.73 ± 0.07) exp(-(425 ± 45)/ T) and partial rate constants for addition-elimination (H + C2H3F) and H atom abstraction (HF + C2H3) pathways of the title reaction: k1a = (0.80 ± 0.07) × 10-10exp(189 ± 37/ T) and k1b = (1.26 ± 0.13) × 10-10exp(-414 ± 45/ T) cm3 molecule-1 s-1, respectively, at T = 298-950 K and with 2σ quoted uncertainties. The overall reaction rate constant can be adequately described by both the temperature independent value and as a sum of k1a and k1b. The kinetic and mechanistic data from the present study are discussed in comparison with previous absolute and relative measurements and theoretical calculations.

Kinetics and Products of the Reaction of OH Radicals with ClNO from 220 to 940 K.

The kinetics and products of the reaction of OH radicals with ClNO have been studied in a flow reactor coupled with an electron impact ionization mass spectrometer at nearly 2 Torr total pressure of helium and over a wide temperature range, T = 220-940 K. The rate constant of the reaction OH + ClNO → products was determined under pseudo-first order conditions, monitoring the kinetics of OH consumption in excess of ClNO: k1 = 1.48 × 10-18 × T2.12 exp(146/T) cm3 molecule-1 s-1 (uncertainty of 15%). HOCl, Cl, and HONO were observed as the reaction products. As a result of quantitative detection of HOCl and Cl, the partial rate constants of the HOCl + NO and Cl + HONO forming reaction pathways were determined in the temperature range 220-940 K: k1a = 3.64 × 10-18 × T1.99 exp(-114/T) and k1b = 4.71 × 10-18 × T1.74 exp(246/T) cm3 molecule-1 s-1 (uncertainty of 20%). The dynamics of the title reaction and, in particular, non-Arrhenius behavior observed for both k1a and k1b in a wide temperature range, seems to be an interesting topic for theoretical research.