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  • 1
    Online Resource
    Online Resource
    Laser ablation with resonance-enhanced multiphoton ionization time-of-flight mass spectrometry for determining aromatic lignin volatilization products from biomass
    AIP Publishing ; 2011
    In:  Review of Scientific Instruments Vol. 82, No. 3 ( 2011-03-01)
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 82, No. 3 ( 2011-03-01)
    Abstract: We have designed and developed a laser ablation/pulsed sample introduction/mass spectrometry platform that integrates pyrolysis (py) and/or laser ablation (LA) with resonance-enhanced multiphoton ionization (REMPI) reflectron time-of-flight mass spectrometry (TOFMS). Using this apparatus, we measured lignin volatilization products of untreated biomass materials. Biomass vapors are produced by either a custom-built hot stage pyrolysis reactor or laser ablation using the third harmonic of an Nd:YAG laser (355 nm). The resulting vapors are entrained in a free jet expansion of He, then skimmed and introduced into an ionization region. One color resonance-enhanced multiphoton ionization (1+1 REMPI) is used, resulting in highly selective detection of lignin subunits from complex vapors of biomass materials. The spectra obtained by py-REMPI-TOFMS and LA-REMPI-TOFMS display high selectivity and decreased fragmentation compared to spectra recorded by an electron impact ionization molecular beam mass spectrometer (EI-MBMS). The laser ablation method demonstrates the ability to selectively isolate and volatilize specific tissues within the same plant material and then detect lignin-based products from the vapors with enhanced sensitivity. The identification of select products observed in the LA-REMPI-TOFMS experiment is confirmed by comparing their REMPI wavelength scans with that of known standards.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/1.3563704
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2011
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 2
    Online Resource
    Online Resource
    Thermal decomposition of CH3CHO studied by matrix infrared spectroscopy and photoionization mass spectroscopy
    AIP Publishing ; 2012
    In:  The Journal of Chemical Physics Vol. 137, No. 16 ( 2012-10-28)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 137, No. 16 ( 2012-10-28)
    Abstract: A heated SiC microtubular reactor has been used to decompose acetaldehyde and its isotopomers (CH3CDO, CD3CHO, and CD3CDO). The pyrolysis experiments are carried out by passing a dilute mixture of acetaldehyde (roughly 0.1%–1%) entrained in a stream of a buffer gas (either He or Ar) through a heated SiC reactor that is 2–3 cm long and 1 mm in diameter. Typical pressures in the reactor are 50–200 Torr with the SiC tube wall temperature in the range 1200–1900 K. Characteristic residence times in the reactor are 50–200 μs after which the gas mixture emerges as a skimmed molecular beam at a pressure of approximately 10 μTorr. The reactor has been modified so that both pulsed and continuous modes can be studied, and results from both flow regimes are presented. Using various detection methods (Fourier transform infrared spectroscopy and both fixed wavelength and tunable synchrotron radiation photoionization mass spectrometry), a number of products formed at early pyrolysis times (roughly 100–200 μs) are identified: H, H2, CH3, CO, CH2=CHOH, HC≡CH, H2O, and CH2=C=O; trace quantities of other species are also observed in some of the experiments. Pyrolysis of rare isotopomers of acetaldehyde produces characteristic isotopic signatures in the reaction products, which offers insight into reaction mechanisms that occur in the reactor. In particular, while the principal unimolecular processes appear to be radical decomposition CH3CHO (+M) → CH3 + H + CO and isomerization of acetaldehyde to vinyl alcohol, it appears that the CH2CO and HCCH are formed (perhaps exclusively) by bimolecular reactions, especially those involving hydrogen atom attacks.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.4759050
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2012
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 3
    Online Resource
    Online Resource
    The products of the thermal decomposition of CH3CHO
    AIP Publishing ; 2011
    In:  The Journal of Chemical Physics Vol. 135, No. 1 ( 2011-07-07)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 135, No. 1 ( 2011-07-07)
    Abstract: We have used a heated 2 cm × 1 mm SiC microtubular (μtubular) reactor to decompose acetaldehyde: CH3CHO + Δ → products. Thermal decomposition is followed at pressures of 75–150 Torr and at temperatures up to 1675 K, conditions that correspond to residence times of roughly 50–100 μs in the μtubular reactor. The acetaldehyde decomposition products are identified by two independent techniques: vacuum ultraviolet photoionization mass spectroscopy (PIMS) and infrared (IR) absorption spectroscopy after isolation in a cryogenic matrix. Besides CH3CHO, we have studied three isotopologues, CH3CDO, CD3CHO, and CD3CDO. We have identified the thermal decomposition products CH3 (PIMS), CO (IR, PIMS), H (PIMS), H2 (PIMS), CH2CO (IR, PIMS), CH2=CHOH (IR, PIMS), H2O (IR, PIMS), and HC≡CH (IR, PIMS). Plausible evidence has been found to support the idea that there are at least three different thermal decomposition pathways for CH3CHO; namely, radical decomposition: CH3CHO + Δ → CH3 + [HCO] → CH3 + H + CO; elimination: CH3CHO + Δ → H2 + CH2=C=O; isomerization/elimination: CH3CHO + Δ → [CH2=CH–OH] → HC≡CH + H2O. An interesting result is that both PIMS and IR spectroscopy show compelling evidence for the participation of vinylidene, CH2=C:, as an intermediate in the decomposition of vinyl alcohol: CH2=CH–OH + Δ → [CH2=C:] + H2O → HC≡CH + H2O.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.3604005
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2011
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 4
    Online Resource
    Online Resource
    Biomass pyrolysis: Thermal decomposition mechanisms of furfural and benzaldehyde
    AIP Publishing ; 2013
    In:  The Journal of Chemical Physics Vol. 139, No. 10 ( 2013-09-14)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 139, No. 10 ( 2013-09-14)
    Abstract: The thermal decompositions of furfural and benzaldehyde have been studied in a heated microtubular flow reactor. The pyrolysis experiments were carried out by passing a dilute mixture of the aromatic aldehydes (roughly 0.1%–1%) entrained in a stream of buffer gas (either He or Ar) through a pulsed, heated SiC reactor that is 2–3 cm long and 1 mm in diameter. Typical pressures in the reactor are 75–150 Torr with the SiC tube wall temperature in the range of 1200–1800 K. Characteristic residence times in the reactor are 100–200 μsec after which the gas mixture emerges as a skimmed molecular beam at a pressure of approximately 10 μTorr. Products were detected using matrix infrared absorption spectroscopy, 118.2 nm (10.487 eV) photoionization mass spectroscopy and resonance enhanced multiphoton ionization. The initial steps in the thermal decomposition of furfural and benzaldehyde have been identified. Furfural undergoes unimolecular decomposition to furan + CO: C4H3O–CHO (+ M) → CO + C4H4O. Sequential decomposition of furan leads to the production of HC≡CH, CH2CO, CH3C≡CH, CO, HCCCH2, and H atoms. In contrast, benzaldehyde resists decomposition until higher temperatures when it fragments to phenyl radical plus H atoms and CO: C6H5CHO (+ M) → C6H5CO + H → C6H5 + CO + H. The H atoms trigger a chain reaction by attacking C6H5CHO: H + C6H5CHO → [C6H6CHO]* → C6H6 + CO + H. The net result is the decomposition of benzaldehyde to produce benzene and CO.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.4819788
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2013
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 5
    Online Resource
    Online Resource
    An optically accessible pyrolysis microreactor
    AIP Publishing ; 2016
    In:  Review of Scientific Instruments Vol. 87, No. 1 ( 2016-01-01)
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 87, No. 1 ( 2016-01-01)
    Abstract: We report an optically accessible pyrolysis micro-reactor suitable for in situ laser spectroscopic measurements. A radiative heating design allows for completely unobstructed views of the micro-reactor along two axes. The maximum temperature demonstrated here is only 1300 K (as opposed to 1700 K for the usual SiC micro-reactor) because of the melting point of fused silica, but alternative transparent materials will allow for higher temperatures. Laser induced fluorescence measurements on nitric oxide are presented as a proof of principle for spectroscopic characterization of pyrolysis conditions.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/1.4939459
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2016
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 6
    Online Resource
    Online Resource
    The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical
    AIP Publishing ; 2016
    In:  The Journal of Chemical Physics Vol. 145, No. 1 ( 2016-07-07)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 145, No. 1 ( 2016-07-07)
    Abstract: Cycloheptatrienyl (tropyl) radical, C7H7, was cleanly produced in the gas-phase, entrained in He or Ne carrier gas, and subjected to a set of flash-pyrolysis micro-reactors. The pyrolysis products resulting from C7H7 were detected and identified by vacuum ultraviolet photoionization mass spectrometry. Complementary product identification was provided by infrared absorption spectroscopy. Pyrolysis pressures in the micro-reactor were roughly 200 Torr and residence times were approximately 100 μs. Thermal cracking of tropyl radical begins at 1100 K and the products from pyrolysis of C7H7 are only acetylene and cyclopentadienyl radicals. Tropyl radicals do not isomerize to benzyl radicals at reactor temperatures up to 1600 K. Heating samples of either cycloheptatriene or norbornadiene never produced tropyl (C7H7) radicals but rather only benzyl (C6H5CH2). The thermal decomposition of benzyl radicals has been reconsidered without participation of tropyl radicals. There are at least three distinct pathways for pyrolysis of benzyl radical: the Benson fragmentation, the methyl-phenyl radical, and the bridgehead norbornadienyl radical. These three pathways account for the majority of the products detected following pyrolysis of all of the isotopomers: C6H5CH2, C6H5CD2, C6D5CH2, and C6H513CH2. Analysis of the temperature dependence for the pyrolysis of the isotopic species (C6H5CD2, C6D5CH2, and C6H513CH2) suggests the Benson fragmentation and the norbornadienyl pathways open at reactor temperatures of 1300 K while the methyl-phenyl radical channel becomes active at slightly higher temperatures (1500 K).
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.4954895
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2016
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 7
    Online Resource
    Online Resource
    Fourier transform infrared absorption spectroscopy of jet-cooled radicals
    AIP Publishing ; 1995
    In:  Review of Scientific Instruments Vol. 66, No. 3 ( 1995-03-01), p. 2430-2441
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 66, No. 3 ( 1995-03-01), p. 2430-2441
    Abstract: We describe an experiment that couples a high-resolution Fourier transform spectrometer (FTS) to a supersonic jet of radicals. A 1-mm-i.d. cylindrical SiC nozzle is resistively heated to 1500 K in order to decompose organic precursors and generate expansions of jet-cooled radicals. We have used this apparatus to pyrolyze alkyl nitrites to make alkoxy and nitric oxide radicals. The residence time of radicals in this hot nozzle is roughly 20 μs RONO→ΔRO+NO. We use the FTS to detect the IR absorption of the product NO (ν0=1876.1 cm−1) at resolutions as fine as 0.005 cm−1 FWHM. We observe the product NO from the pyrolysis of CH3CH2ONO to be rotationally cooled to roughly 50 K. The IR spectra indicate that the optical path length is about 3/4 cm and that the nitrites pyrolyze to produce approximately 1014 NO radicals cm−3 some 9 mm downstream from the nozzle. Our spectrometer is capable of detecting an absorption signal of 0.1% over a bandwidth of 100 cm−1 at 0.005 cm−1 resolution. Depending on the infrared cross section of the radical, this implies that we are able to monitor diatomic radical densities of roughly 5×1012 cm−3 (quantum state)−1.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/1.1145641
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1995
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 8
    Online Resource
    Online Resource
    The thermal decomposition of the benzyl radical in a heated micro-reactor. I. Experimental findings
    AIP Publishing ; 2015
    In:  The Journal of Chemical Physics Vol. 142, No. 4 ( 2015-01-28)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 142, No. 4 ( 2015-01-28)
    Abstract: The pyrolysis of the benzyl radical has been studied in a set of heated micro-reactors. A combination of photoionization mass spectrometry (PIMS) and matrix isolation infrared (IR) spectroscopy has been used to identify the decomposition products. Both benzyl bromide and ethyl benzene have been used as precursors of the parent species, C6H5CH2, as well as a set of isotopically labeled radicals: C6H5CD2, C6D5CH2, and C6H513CH2. The combination of PIMS and IR spectroscopy has been used to identify the earliest pyrolysis products from benzyl radical as: C5H4=C=CH2, H atom, C5H4—C ≡ CH, C5H5, HCCCH2, and HC ≡ CH. Pyrolysis of the C6H5CD2, C6D5CH2, and C6H513CH2 benzyl radicals produces a set of methyl radicals, cyclopentadienyl radicals, and benzynes that are not predicted by a fulvenallene pathway. Explicit PIMS searches for the cycloheptatrienyl radical were unsuccessful, there is no evidence for the isomerization of benzyl and cycloheptatrienyl radicals: C6H5CH2⇋C7H7. These labeling studies suggest that there must be other thermal decomposition routes for the C6H5CH2 radical that differ from the fulvenallene pathway.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.4906156
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2015
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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