The thermal decomposition of oxolan-3-one, a common component of the bio-oil formed during biomass pyrolysis, has been studied using ab initio calculations and experiments employing pulsed gas-phase ...pyrolysis with matrix-isolation FTIR product detection. Four pathways for unimolecular decomposition were predicted using computational methods. The dominant reaction channel led to carbon monoxide, formaldehyde, and ethylene, all of which were observed experimentally. The other channels led to an assortment of products including ketene, water, propyne, and acetylene, which were all confirmed in the matrix-isolation FTIR spectra. There is also evidence for the production of substituted ketenes in pyrolysis, most likely hydroxyketene and methylketene.
Vibrational Bands of the 2‑Butyn-1-yl Radical Brown, Glenna J; Ellis, Martha J; Martin, Thaddeus D ...
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
05/2020, Letnik:
124, Številka:
20
Journal Article
Recenzirano
Odprti dostop
The 2-butyn-1-yl radical is an isomer of C4H5 and is structurally similar to the propargyl radical, which is the simplest resonance-stabilized hydrocarbon radical. The C4H5 radical is likely to be ...important to astrochemistry and combustion, similar to propargyl, yet little research has been done on its spectroscopic properties. In this work, seven vibrational bands of the 2-butyn-1-yl radical are reported. The radical was formed by pyrolysis of 1-bromo-2-butyne at 800 K and isolated in a low-temperature argon matrix. The experimentally observed frequencies and intensities of the seven vibrational bands were found to be consistent with QCISD predictions from the literature and with new B3LYP calculations in this work.
To clarify the nature of the motions contributing to the observed multiplet structures in the low-energy (900−1800 cm-1) vibrational spectrum of the H5O2 + “Zundel” ion, we report the evolution of ...its vibrational fingerprint with sequential H/D isotopic substitution in a predissociation study of the Ar complexes. Of particular interest is the D4HO2 + complex, which displays a single intense band in the vicinity of the asymmetric OHO stretch of the bridging proton, in contrast to the more complex multiplet observed for both H5O2 + and D5O2 + isotopologues. These intensity patterns are consistent with the recent assignment of the bridging proton band's doublet in the H5O2 +·Ne spectrum to a 2 × 2 Fermi resonance interaction between the shared proton stretch and a complex background level primarily derived from the O−O stretch together with two quanta of the wagging vibration involving the pyramidal deformations of the flanking H2O groups (Vendrell, O.; Gatti, F.; Meyer, H.-D. Angew. Chem., Int. Ed. 2007, 46, 6918). In addition, the observed trends rule out assignment of the ∼1800 cm-1 feature in H5O2 + to a combination band of the bridging proton vibration with the O−O stretch, providing a secure foundation for the previously reported scheme that attributes this band to the out-of-phase intramolecular bending fundamental. The observed feature occurs at an unusually high energy for typical HOH bends, however, and we explore the participation of the bridging proton in these eigenstates by following how the calculated harmonic spectrum evolves when artificially large masses are assigned to the proton. The empirical assignments are supported by anharmonic estimates of the isotope shifts evaluated by the diffusion Monte Carlo method.
Zero‐point energy matters: In strong, low‐barrier hydrogen bonds, quantum effects cause a structural symmetrization (see picture). Together with the pronounced anharmonicity of vibrational motion, ...this situation gives rise to peculiar infrared (IR) spectral signatures in the region below 2000 cm−1. For the shared proton in N2H7+, the IR spectrum is elucidated by combining two experimental techniques with anharmonic quantum calculations.
Pyrolysis Reactions of 3‑Oxetanone Wright, Emily M; Warner, Brian J; Foreman, Hannah E ...
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
07/2015, Letnik:
119, Številka:
29
Journal Article
Recenzirano
The pyrolysis products of gas-phase 3-oxetanone were identified via matrix-isolation Fourier transform infrared spectroscopy and photoionization mass spectrometry. Pyrolysis was conducted in a ...hyperthermal nozzle at temperatures from 100 to 1200 °C with the dissociation onset observed at ∼600 °C. The ring strain in the cyclic structure of 3-oxetanone causes the molecule to decompose at relatively low temperatures. Previously, only one dissociation channel, producing formaldehyde and ketene, was considered as significant in photolysis. This study presents the first experimental measurements of the thermal decomposition of 3-oxetanone demonstrating an additional dissociation channel that forms ethylene oxide and carbon monoxide. Major products include formaldehyde, ketene, carbon monoxide, ethylene oxide, ethylene, and methyl radical. The first four products stem from initial decomposition of 3-oxetanone, while the additional products, ethylene and methyl radical, are believed to be due to further reactions involving ethylene oxide.
•Pyrolysis products of isovaleraldehyde and pivaldehyde are identified.•Aldehydes with branched alkyl groups decompose similarly to unbranched aldehydes.•Pivaldehyde produces fewer unique products ...than isovaleraldehyde.
The thermal decomposition of gas-phase isovaleraldehyde, (CH3)2CHCH2CHO, and pivaldehyde, (CH3)3CCHO, was studied in the 1270–1470K range to determine the effect of alkyl chain structure on the decomposition mechanism of aliphatic aldehydes. Pyrolysis was performed with a pulsed hyperthermal nozzle and the products were identified via matrix-isolation Fourier transform infrared spectroscopy. The products of isovaleraldehyde pyrolysis were carbon monoxide, isobutene, water, 3-methyl-1-butyne, isopropylketene, vinyl alcohol, propene, acetaldehyde, acetylene, propyne, methane, ethylene, and ketene. The products of pivaldehyde pyrolysis were carbon monoxide, isobutene, propene, acetaldehyde, acetylene, propyne, methane, ethylene, and ketene. The reduced number of products from pivaldehyde, as compared to isovaleraldehyde, is due to the fully branched chain structure of the pivaldehyde backbone. The differences between the results for isovaleraldehyde and pivaldehyde lend support to the proposed reactions occurring early in the pyrolysis mechanism. However, the presence of acetylene, propyne, methane, ethylene, and ketene cannot easily be explained and points to the need for further exploration of the mechanisms.
Products From Pyrolysis of Gas-Phase Propionaldehyde Warner, Brian J; Wright, Emily M; Foreman, Hannah E ...
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
01/2015, Letnik:
119, Številka:
1
Journal Article
Recenzirano
A hyperthermal nozzle was utilized to study the thermal decomposition of propionaldehyde, CH3CH2CHO, over a temperature range of 1073–1600 K. Products were identified with two detection methods: ...matrix-isolation Fourier transform infrared spectroscopy and photoionization mass spectrometry. Evidence was observed for four reactions during the breakdown of propionaldehyde: α–C-C bond scission yielding CH3CH2, CO, and H, an elimination reaction forming methylketene and H2, an isomerization pathway leading to propyne via the elimination of H2O, and a β–C-C bond scission channel forming methyl radical and •CH2CHO. The products identified during this experiment were CO, HCO, CH3CH2, CH3CHCO, H2O, CH3CCH, CH3, H2CCO, CH2CH2, CH3CHCH2, HCCH, CH2CCH, H2CO, C4H2, C4H4, and CH3CHO. The first eight products result from primary or bimolecular reactions involving propionaldehyde while the remaining products occur from reactions including the initial pyrolysis products. While the pyrolysis of propionaldehyde involves reactions similar to those observed for acetaldehyde and butyraldehyde in recent studies, there are a few unique products observed which highlight the need for further study of the pyrolysis mechanism.
Electron energy-resolved vibrational autodetachment from OH stretching fundamentals in the water hexamer anion.
We exploit the high collection efficiency of negative ion photoelectron imaging for low ...energy electrons to monitor the energy and angular distributions of the photoelectrons arising from vibrational excitation of the water hexamer anion in the vicinity of the OH stretching fundamentals. Photoelectrons from the low electron binding energy isomer (type II) appear as a smoothly varying outer ring with the anisotropic angular distribution expected for direct photodetachment. The higher binding isomer (type I) yields very slow electrons that are strongly modulated through the OH stretching resonances, which are discussed in the context of a statistical (IVR-based) ejection mechanism.
Recently, we reported the spectrum of Ar·D4HO2 + McCunn; et, al. J. Phys. Chem. B 2008, 112, 321, and here, we extend that work to include the Ar·H4DO2 + isotopologue in order to explore why the Ar ...atom has a much greater propensity for attachment to a dangling OD group than it does for OH, even when many more of the latter binding sites are available. Calculated (MP2/6-311+G(d,p) level of theory/basis) harmonic frequencies reproduce the observed multiplet patterns of OH and OD stretches and confirm the presence of various isomers arising from the different Ar binding sites. The preferential bonding of Ar to OD is traced to changes in the frequencies of the wag and rock modes of the H5O2 + moiety rather than to shifts in the oscillator that directly binds the Ar atom.
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