Engineering topics

Troy, Tyler P.

Publications and source records attributed to Troy, Tyler P..

16 records

DOE OSTI2020

Exciton energy transfer reveals spectral signatures of excited states in clusters

Electronic excitation and concomitant energy transfer leading to Penning ionization in argon–acetylene clusters generated in a supersonic expansion are investigated with synchrotron-based photoionization mass spectrometry and electronic structure calculations. Spectral features in the photoionization efficiency of the mixed argon–acetylene clusters reveal a blue shift from the 2 P 1/2 and 2 P 3/2 excited states of atomic argon. Analysis of this feature suggests that excited states of argon clusters transfer energy to acetylene, resulting in its ionization and successive evaporation of argon. Theoretically calculated Ar n (n = 2–6) cluster spectra are in excellent agreement with experimental observations, and provide insight into the structure and ionization dynamics of the clusters. A comparison between argon–acetylene and argon–water clusters reveals that argon solvates water better, allowing for higher-order excitons and Rydberg states to be populated. Furthermore, these results are explained by theoretical calculations of respective binding energies and structures.

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DOE OSTI2018

Enabling liquid vapor analysis using synchrotron VUV single photon ionization mass spectrometry with a microfluidic interface

Vacuum ultraviolet (VUV) single photon ionization mass spectrometry (SPI-MS) is a vacuum-based technique typically used for analysis of gas phase and solid samples, but not for liquids, due to the challenge in proposing volatile liquids in vacuum. In this work we introduce the first demonstration of in situ liquid analysis by integrating the System for Analysis at the Liquid Vacuum Interface (SALVI) microfluidic reactor into VUV SPI-MS. Four representative volatile organic compound (VOC) solutions were used to illustrate feasibility of liquid analysis. Our results reflect accurate mass identification of the VOC molecules and reliable determination of appearance energy (AE) that is consistent with ionization energy (IE) for gaseous species in literature as reported. This work validates that the vacuum-compatible SALVI microfluidic interface can be utilized at the synchrotron beamline and enable in situ research of gas-phase molecules evaporating off the surface of a liquid, which holds importance in the study of condensed matter chemistry.

47 OTHER INSTRUMENTATION↗

DOE OSTI2018

Thermal Decompositions of the Lignin Model Compounds: Salicylaldehyde and Catechol

Here, the nascent steps in the pyrolysis of the lignin components salicylaldehyde (o-HOC 6 H 4 CHO) and catechol (o-HOC 6 H 4 OH) were studied in a set of heated microreactors. The microreactors are small (roughly 1 mm ID x 3 cm long); transit times through the reactors are about 100 us. Temperatures in the microreactors can be as high as 1600 K, and pressures are typically a few hundred torr. The products of pyrolysis are identified by a combination of photoionization mass spectrometry, photoelectron photoion concidence mass spectroscopy, and matrix isolation infrared spectroscopy. The main pathway by which salicylaldehyde decomposes is a concerted fragmentation: o-HOC 6 H 4 CHO (+ M) → H 2 + CO + C 5 H 4 -C-O (fulveneketene). At temperatures above 1300 K, fulveneketene loses CO to yield a mixture of HC=C-C=C-CH 3 , HC=C-CH 2 -C=CH, and HC=C-CH-C-CH 2 . These alkynes decompose to a mixture of radicals (HC=C-C=C-CH 2 and HC=C-CH-C=CH) and H atoms. H-atom chain reactions convert salicylaldehyde to phenol: o-HOC 6 H 4 CHO + H → C 6 H 5 OH + CO + H. Catechol has similar chemistry to salicylaldehyde. Electrocyclic fragmentation produces water and fulveneketene: o-HOC 6 H 4 OH (+ M) → H 2 O + C 5 H 4 -C-O. These findings have implications for the pyrolysis of lignin itself.

09 BIOMASS FUELS↗

DOE OSTI2017

Two coexisting liquid phases in switchable ionic liquids

Switchable ionic liquids (SWILs) derived from organic bases and alcohols are attractive due to their applications in gas capture, separations, and nanomaterial synthesis. However, their exact solvent structure still remains a mystery. Here, we present the first chemical mapping of a SWIL solvent structure using in situ time-of-flight secondary ion mass spectrometry. In situ chemical mapping discovers two coexisting liquid phases and molecular structures vastly different from conventional ionic liquids. SWIL chemical speciation is found to be more complex than the known stoichiometry. Dimers and ionic clusters have been identified in SIMS spectra; and confirmed to be the chemical species differentiating from non-ionic liquids via spectral principal component analysis. Our unique in situ molecular imaging has advanced the understanding of SWIL chemistry and how this “heterogeneous” liquid structure may impact SWILs’ physical and thermodynamic properties and associated applications.

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DOE OSTI2017

Ab initio dynamics and photoionization mass spectrometry reveal ion–molecule pathways from ionized acetylene clusters to benzene cation

Significance The formation of benzene and its cation constitutes a likely gateway to polycyclic aromatic hydrocarbons, which are the bridge to larger carbonaceous material such as soot in combustion processes and interstellar dust. Our paper reports computational and experimental results that address the long-standing puzzle of how ion–molecule reactions involving small unsaturated organics, such as acetylene, which is widespread in the interstellar medium, can lead to benzene cation. We present insights into the facile way in which C 6 H 6 + products, including benzene cation, can be accessed after ionization of cold isolated neutral clusters, and show that there is a catalytic role for what are nominally spectator acetylene molecules.

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DOE OSTI2017

A vacuum ultraviolet photoionization study on high-temperature decomposition of JP-10 (exo-tetrahydrodicyclopentadiene)

Here, two sets of experiments were performed to unravel the high-temperature pyrolysis of tricyclo[5.2.1.02,6] decane (JP-10) exploiting high-temperature reactors over a temperature range of 1100 K to 1600 K, Advanced Light Source (ALS), and 927 K to 1083 K, National Synchrotron Radiation Laboratory (NSRL), with residence times of a few tens of microseconds (ALS) to typically 144 ms (NSRL). The products were identified in situ in supersonic molecular beams via single photon vacuum ultraviolet (VUV) photoionization coupled with mass spectroscopic detection in a reflectron time-of-flight mass spectrometer (ReTOF). These studies were designed to probe the initial (ALS) and also higher order reaction products (NSRL) formed in the decomposition of JP-10 – including radicals and thermally labile closed-shell species. Altogether 43 products were detected and quantified including C1–C4 alkenes, dienes, C3–C4 cumulenes, alkynes, eneynes, diynes, cycloalkenes, cyclo-dienes, aromatic molecules, and most importantly, radicals such as ethyl, allyl, and methyl produced at shorter residence times. At longer residence times, the predominant fragments were molecular hydrogen (H 2 ), ethylene (C 2 H 4 ), propene (C 3 H 6 ), cyclopentadiene (C 5 H 6 ), cyclopentene (C 5 H 8 ), fulvene (C 6 H 6 ), and benzene (C 6 H 6 ). Accompanied by electronic structure calculations, the initial JP-10 decomposition via C–H bond cleavages resulting in the formation of the initial six C 10 H 15 radicals was found to explain the formation of all products detected in both sets of experiments. These radicals are not stable under the experimental conditions and further decompose via C–C bond β-scission processes. These pathways result in ring opening in the initial tricyclic carbon skeletons of JP-10. Intermediates accessed after the first β-scission can further isomerize or dissociate. Complex PAH products in the NRLS experiment (naphthalene, acenaphthylene, biphenyl) are likely formed via molecular growth reactions at elevated residence times.

10 SYNTHETIC FUELS↗

DOE OSTI2017

HACA's Heritage: A Free‐Radical Pathway to Phenanthrene in Circumstellar Envelopes of Asymptotic Giant Branch Stars

Abstract The hydrogen‐abstraction/acetylene‐addition (HACA) mechanism has been central for the last decades in attempting to rationalize the formation of polycyclic aromatic hydrocarbons (PAHs) as detected in carbonaceous meteorites such as in Murchison. Nevertheless, the basic reaction mechanisms leading to the formation of even the simplest tricyclic PAHs like anthracene and phenanthrene are still elusive. Here, by exploring the previously unknown chemistry of the ortho ‐biphenylyl radical with acetylene, we deliver compelling evidence on the efficient synthesis of phenanthrene in carbon‐rich circumstellar environments. However, the lack of formation of the anthracene isomer implies that HACA alone cannot be responsible for the formation of PAHs in extreme environments. Considering the overall picture, alternative pathways such as vinylacetylene‐mediated reactions are required to play a crucial role in the synthesis of complex PAHs in circumstellar envelopes of dying carbon‐rich stars.

Yang, Tao↗

DOE OSTI2017

HACA's Heritage: A Free-Radical Pathway to Phenanthrene in Circumstellar Envelopes of Asymptotic Giant Branch Stars

The hydrogen-abstraction/acetylene-addition (HACA) mechanism has been central for the last decades in attempting to rationalize the formation of polycyclic aromatic hydrocarbons (PAHs) as detected in carbonaceous meteorites such as in Murchison. Nevertheless, the basic reaction mechanisms leading to the formation of even the simplest tricyclic PAHs like anthracene and phenanthrene are still elusive. By exploring the previously unknown chemistry of the ortho -biphenylyl radical with acetylene, we deliver compelling evidence on the efficient synthesis of phenanthrene in carbon-rich circumstellar environments. However, the lack of formation of the anthracene isomer implies that HACA alone cannot be responsible for the formation of PAHs in extreme environments. Considering the overall picture, alternative pathways such as vinylacetylene-mediated reactions are required to play a crucial role in the synthesis of complex PAHs in circumstellar envelopes of dying carbon-rich stars.

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DOE OSTI2017

Combined Experimental and Computational Study on the Unimolecular Decomposition of JP-8 Jet Fuel Surrogates. I. n-Decane (n-C 10 H 22 )

Exploiting a high temperature chemical reactor, we explored in this paper the pyrolysis of helium-seeded n-decane as a surrogate of the n-alkane fraction of Jet Propellant-8 (JP-8) over a temperature range of 1100–1600 K at a pressure of 600 Torr. The nascent products were identified in situ in a supersonic molecular beam via single photon vacuum ultraviolet (VUV) photoionization coupled with a mass spectroscopic analysis of the ions in a reflectron time-of-flight mass spectrometer (ReTOF). Our studies probe, for the first time, the initial reaction products formed in the decomposition of n-decane—including radicals and thermally labile closed-shell species effectively excluding mass growth processes. The present study identified 18 products: molecular hydrogen (H 2 ), C2 to C7 1-alkenes [ethylene (C 2 H 4 ) to 1-heptene (C 7 H 14 )], C1–C3 radicals [methyl (CH 3 ), vinyl (C 2 H 3 ), ethyl (C 2 H 5 ), propargyl (C 3 H 3 ), allyl (C 3 H 5 )], small C1–C3 hydrocarbons [methane (CH 4 ), acetylene (C 2 H 2 ), allene (C 3 H 4 ), methylacetylene (C 3 H 4 )], along with higher-order reaction products [1,3-butadiene (C 4 H 6 ), 2-butene (C 4 H 8 )]. On the basis of electronic structure calculations, n-decane decomposes initially by C–C bond cleavage (excluding the terminal C–C bonds) producing a mixture of alkyl radicals from ethyl to octyl. These alkyl radicals are unstable under the experimental conditions and rapidly dissociate by C–C bond β-scission to split ethylene (C 2 H 4 ) plus a 1-alkyl radical with the number of carbon atoms reduced by two and 1,4-, 1,5-, 1,6-, or 1,7-H shifts followed by C–C β-scission producing alkenes from propene to 1-octene in combination with smaller 1-alkyl radicals. The higher alkenes become increasingly unstable with rising temperature. When the C–C β-scission continues all the way to the propyl radical (C 3 H 7 ), it dissociates producing methyl (CH 3 ) plus ethylene (C 2 H 4 ). Also, at higher temperatures, hydrogen atoms can abstract hydrogen from C 10 H 22 to yield n-decyl radicals, while methyl (CH 3 ) can also abstract hydrogen or recombine with hydrogen to form methane. Finally, these n-decyl radicals can decompose via C–C-bond β-scission to C3 to C9 alkenes.

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DOE OSTI2017

Combined Experimental and Computational Study on the Unimolecular Decomposition of JP-8 Jet Fuel Surrogates. II: n-Dodecane (n-C 12 H 26 )

In this paper, we investigated temperature-dependent products in the pyrolysis of helium-seeded n-dodecane, which represents a surrogate of the n-alkane fraction of Jet Propellant-8 (JP-8) aviation fuel. The experiments were performed in a high temperature chemical reactor over a temperature range of 1200 K to 1600 K at a pressure of 600 Torr, with in situ identification of the nascent products in a supersonic molecular beam using single photon vacuum ultraviolet (VUV) photoionization coupled with the analysis of the ions in a reflectron time-of-flight mass spectrometer (ReTOF). For the first time, the initial decomposition products of n-dodecane—including radicals and thermally labile closed-shell species—were probed in experiments, which effectively exclude mass growth processes. A total of 15 different products were identified, such as molecular hydrogen (H 2 ), C2 to C7 1-alkenes [ethylene (C 2 H 4 ) to 1-heptene (C 7 H 14 )], C1–C3 radicals [methyl (CH 3 ), ethyl (C 2 H 5 ), allyl (C 3 H 5 )], small C1–C3 hydrocarbons [acetylene (C 2 H 2 ), allene (C 3 H 4 ), methylacetylene (C 3 H 4 )], as well as the reaction products [1,3-butadiene (C 4 H 6 ), 2-butene (C 4 H 8 )] attributed to higher-order processes. Electronic structure calculations carried out at the G3(CCSD,MP2)//B3LYP/6-311G(d,p) level of theory combined with RRKM/master equation of rate constants for relevant reaction steps showed that n-dodecane decomposes initially by a nonterminal C–C bond cleavage and producing a mixture of alkyl radicals from ethyl to decyl with approximately equal branching ratios. The alkyl radicals appear to be unstable under the experimental conditions and to rapidly dissociate either directly by C–C bond β-scission to produce ethylene (C 2 H 4 ) plus a smaller 1-alkyl radical with the number of carbon atoms diminished by two or via 1,5-, 1,6-, or 1,7- 1,4-, 1,9-, or 1,8-H shifts followed by C–C β-scission producing alkenes from propene to 1-nonene together with smaller 1-alkyl radicals. The stability and hence the branching ratios of higher alkenes decrease as temperature increases. The C–C β-scission continues all the way to the propyl radical (C 3 H 7 ), which dissociates to methyl (CH 3 ) plus ethylene (C 2 H 4 ). Finally, in addition, at higher temperatures, another mechanism can contribute, in which hydrogen atoms abstract hydrogen from C 12 H 26 producing various n-dodecyl radicals and these radicals then decompose by C–C bond β-scission to C3 to C11 alkenes.

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DOE OSTI2016

Hydrogen-Abstraction/Acetylene-Addition Exposed

Polycyclic aromatic hydrocarbons (PAHs) are omnipresent in the interstellar medium (ISM) and also in carbonaceous meteorites (CM) such as Murchison. However, the basic reaction routes leading to the formation of even the simplest PAH—naphthalene (C 10 H 8 )—via the hydrogen-abstraction/acetylene-addition (HACA) mechanism still remain ambiguous. Here, by revealing the uncharted fundamental chemistry of the styrenyl (C 8 H 7 ) and the ortho-vinylphenyl radicals (C 8 H 7 )—key transient species of the HACA mechanism—with acetylene (C 2 H 2 ), we provide the first solid experimental evidence on the facile formation of naphthalene in a simulated combustion environment validating the previously postulated HACA mechanism for these two radicals. Lastly, this study highlights, at the molecular level spanning combustion and astrochemistry, the importance of the HACA mechanism to the formation of the prototype PAH naphthalene.

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DOE OSTI2016

Hydrogen-Abstraction/Acetylene-Addition Exposed

Polycyclic aromatic hydrocarbons (PAHs) are omnipresent in the interstellar medium (ISM) and also in carbonaceous meteorites (CM) such as Murchison. However, the basic reaction routes leading to the formation of even the simplest PAH—naphthalene (C 10 H 8 )—via the hydrogen-abstraction/acetylene-addition (HACA) mechanism still remain ambiguous. By revealing the uncharted fundamental chemistry of the styrenyl (C 8 H 7 ) and the ortho-vinylphenyl radicals (C 8 H 7 )—key transient species of the HACA mechanism—with acetylene (C 2 H 2 ), we provide the first solid experimental evidence on the facile formation of naphthalene in a simulated combustion environment validating the previously postulated HACA mechanism for these two radicals. This study highlights, at the molecular level spanning combustion and astrochemistry, the importance of the HACA mechanism to the formation of the prototype PAH naphthalene.

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DOE OSTI2016

Proton transfer in acetaldehyde–water clusters mediated by a single water molecule

Proton transfer in aqueous media is a ubiquitous process, occurring in acid–base chemistry, biology, and in atmospheric photochemistry. Photoionization mass spectrometry coupled with theoretical calculations demonstrate that a relay-type proton transfer mechanism is operational for single-water-molecule-assisted proton transfer between two acetaldehyde molecules in the gas phase. Threshold photoionization of acetaldehyde–water clusters leads to proton transfer between the formyl groups (–CH=O) of one acetaldehyde molecule to another, and the subsequent formation of cationic moieties. Density functional theory computations reveal several plausible pathways of proton transfer in mixed cluster cations. Among these pathways, water-mediated proton transfer is energetically favored. Finally, mass spectra and photoionization efficiency curves confirm these theoretical findings and also demonstrate the increased stability of cluster cations where acetaldehyde molecules are symmetrically bonded to the hydronium ion.

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DOE OSTI2016

The thermal decomposition of the benzyl radical in a heated micro-reactor. II. Pyrolysis of the tropyl radical

Cycloheptatrienyl (tropyl) radical, C{sub 7}H{sub 7}, 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 C{sub 7}H{sub 7} 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 C{sub 7}H{sub 7} 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 (C{sub 7}H{sub 7}) radicals but rather only benzyl (C{sub 6}H{sub 5}CH{sub 2}). 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: C{sub 6}H{sub 5}CH{sub 2}, C{sub 6}H{sub 5}CD{sub 2}, C{sub 6}D{sub 5}CH{sub 2}, and C{sub 6}H{sub 5}{sup 13}CH{sub 2}. Analysis of the temperature dependence for the pyrolysis of the isotopic species (C{sub 6}H{sub 5}CD{sub 2}, C{sub 6}D{sub 5}CH{sub 2}, and C{sub 6}H{sub 5}{sup 13}CH{sub 2}) 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).

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DOE OSTI2016

Pyrolysis of the Simplest Carbohydrate, Glycolaldehyde (CHO-CH 2 OH), and Glyoxal in a Heated Microreactor

Both glycolaldehyde and glyoxal were pyrolyzed in a set of flash-pyrolysis microreactors. The pyrolysis products resulting from CHO-CH 2 OH and HCO-CHO were detected and identified by vacuum ultraviolet (VUV) photoionization mass spectrometry. Complementary product identification was provided by argon matrix infrared absorption spectroscopy. Pyrolysis pressures in the microreactor were about 100 Torr, and contact times with the microreactors were roughly 100 μs. At 1200 K, the products of glycolaldehyde pyrolysis are H atoms, CO, CH 2 =O, CH 2 =C=O, and HCO-CHO. Thermal decomposition of HCO-CHO was studied with pulsed 118.2 nm photoionization mass spectrometry and matrix infrared absorption. Under these conditions, glyoxal undergoes pyrolysis to H atoms and CO. Tunable VUV photoionization mass spectrometry provides a lower bound for the ionization energy IE (CHO-CH 2 OH) ≥ 9.95 ± 0.05 eV. The gas-phase heat of formation of glycolaldehyde was established by a sequence of calorimetric experiments. The experimental result is Δ f H 298 (CHO-CH 2 OH) = -75.8 ± 1.3 kcal mol -1 . Fully ab initio , coupled cluster calculations predict Δ f H 0 (CHO-CH 2 OH) of -73.1 ± 0.5 kcal mol -1 and Δ f H 298 (CHO-CH 2 OH) of -76.1 ± 0.5 kcal mol -1 . The coupled-cluster singles doubles and noniterative triples correction calculations also lead to a revision of the geometry of CHO-CH 2 OH. We have found that the O-H bond length differs substantially from earlier experimental estimates, due to unusual zero-point contributions to the moments of inertia.

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DOE OSTI2015

Isomerization and Fragmentation of Cyclohexanone in a Heated Micro-Reactor

Here, the thermal decomposition of cyclohexanone (C 6 H 10 =O) has been studied in a set of flash-pyrolysis microreactors. Decomposition of the ketone was observed when dilute samples of C 6 H 10 =O were heated to 1200 K in a continuous flow microreactor. Pyrolysis products were detected and identified by tunable VUV photoionization mass spectroscopy and by photoionization appearance thresholds. Complementary product identification was provided by matrix infrared absorption spectroscopy. Pyrolysis pressures were roughly 100 Torr, and contact times with the microreactors were roughly 100 μs. Thermal cracking of cyclohexanone appeared to result from a variety of competing pathways, all of which open roughly simultaneously. Isomerization of cyclohexanone to the enol, cyclohexen-1-ol (C 6 H 9 OH), is followed by retro-Diels–Alder cleavage to CH 2 =CH 2 and CH 2 =C(OH)–CH=CH 2 . Further isomerization of CH 2 =C(OH)–CH=CH 2 to methyl vinyl ketone (CH 3 CO–CH=CH 2 , MVK) was also observed. Photoionization spectra identified both enols, C 6 H 9 OH and CH 2 =C(OH)–CH=CH 2 , and the ionization threshold of C 6 H 9 OH was measured to be 8.2 ± 0.1 eV. Coupled cluster electronic structure calculations were used to establish the energetics of MVK. The heats of formation of MVK and its enol were calculated to be Δ f H 298 (cis-CH 3 CO–CH=CH 2 ) = -26.1 ± 0.5 kcal mol –1 and Δ f H 298 (s-cis-1-CH 2 =C(OH)–CH=CH 2 ) = -13.7 ± 0.5 kcal mol –1 . The reaction enthalpy Δ rxn H 298 (C 6 H 10 =O → CH 2 =CH 2 + s-cis-1-CH 2 =C(OH)–CH=CH 2 ) is 53 ± 1 kcal mol –1 and Δ rxn H 298 (C 6 H 10 =O → CH 2 =CH 2 + cis-CH 3 CO–CH=CH 2 ) is 41 ± 1 kcal mol –1 . At 1200 K, the products of cyclohexanone pyrolysis were found to be C 6 H 9 OH, CH 2 =C(OH)–CH=CH 2 , MVK, CH 2 CHCH 2 , CO, CH 2 =C=O, CH 3 , CH 2 =C=CH 2 , CH 2 =CH–CH=CH 2 , CH 2 =CHCH 2 CH 3 , CH 2 =CH 2 , and HC≡CH.

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