HCO Radical Research Articles

Study of Complex Nitrogen and Oxygen-bearing Molecules toward the High-mass Protostar IRAS 18089–1732

The observation of oxygen (O)- and nitrogen (N)-bearing molecules gives an idea about the complex prebiotic chemistry in the interstellar medium. Recent millimeter and submillimeter wavelength observations have shown the presence of complex O- and N-bearing molecules in the star formation regions. So, the investigation of those molecules is crucial to understanding the chemical complexity in the star-forming regions. In this article, we present the identification of the rotational emission lines of N-bearing molecules ethyl cyanide ( C2H5CN ) and cyanoacetylene (HC3N), and O-bearing molecule methyl formate (CH3OCHO) toward high-mass protostar IRAS 18089–1732 using the Atacama Compact Array. We also detected the emission lines of both the N- and O-bearing molecule formamide (NH2CHO) in the envelope of IRAS 18089–1732. We have detected the v = 0 and 1 state rotational emission lines of CH3OCHO. We also detected the two vibrationally excited states of HC3N (v7 = 1 and v7 = 2). The estimated fractional abundances of C2H5CN , HC3N (v7 = 1), HC3N (v7 = 2), and NH2CHO toward IRAS 18089–1732 are (1.40 ± 0.5) × 10−10, (7.5 ± 0.7) × 10−11, (3.1 ± 0.4) × 10−11, and (6.25 ± 0.82) × 10−11 respectively. Similarly, the estimated fractional abundances of CH3OCHO (v = 0) and CH3OCHO (v = 1) are (1.90 ± 0.9) × 10−9 and (8.90 ± 0.8) × 10−10, respectively. We also created the integrated emission maps of the detected molecules, and the observed molecules may have originated from the extended envelope of the protostar. We show that C2H5CN and HC3N are most probably formed via the subsequential hydrogenation of the CH2CHCN and the reaction between C2H2 and CN on the grain surface of IRAS 18089–1732. We found that NH2CHO is probably produced due to the reaction between NH2 and H2CO in the gas phase. Similarly, CH3OCHO is possibly created via the reaction between radical CH3O and radical HCO on the grain surface of IRAS 18089–1732.

Laminar flame speed measurement and combustion mechanism optimization of methanol–air mixtures

AbstractLaminar flame speeds of methanol/air mixtures at 338–398 K are measured by the heat flux method, extending the range of equivalence ratio up to 2.1. And a new optimized methanol mechanism with 94 reactions is proposed by using the particle swarm algorithm, adjusting 20 Arrhenius pre‐exponential factors in their uncertainty domains. The optimized model is compared with eight methanol combustion mechanisms and experimental data published in recent years, covering a wide range of initial temperatures (298–1537 K), pressures (0.04–50 atm) and equivalence ratios (0.5–2.1). The results show that the optimized mechanism not only improves the accuracy of ignition delay time with rapid compression machine at low temperature but also moderately improve the description of laminar flame speed in lean and stoichiometric conditions. Meanwhile, the optimized model significantly enhances the prediction accuracy of CH3 and CH2O radical, and perfectly captures the evolution trend of HCO radical in laminar flat flame. Overall, the optimized mechanism provides the best overall description of the currently available measurements, leading to more accurate and comprehensive prediction of ignition delay time, laminar flame speed and species concentration.

Experimental and computational (Chemical Kinetic + CFD) analyses of Self-Recuperative annular tubular porous burner for NH3/CH4 -air Non-Premixed combustion

Ammonia is now being explored as a potential gas turbine fuel because of its renewable and carbon-free nature. Ammonia combustion possesses various limitations, such as high NO emissions, low burning velocity, and high auto-ignition temperature. Moreover, dual-fuel combustion approaches can be used to mitigate these drawbacks. However, the limitations of available information about the resulting emissions are insufficient to encourage widespread adoption. In this work, an NH3/CH4-air fueled self-recuperative high aspect ratio annular tubular porous burner is developed for gas turbine power applications. In this burner, an annular zone surrounds the combustion chamber to preheat the incoming air, while two perforated discs are mounted between the combustor and annular zone for uniform distribution of air. Eight Zirconia foams (4 of 10 PPI and 4 of 20 PPI) are stacked at the upstream side of the combustor. Experimentally, air preheat temperature, combustor exit temperature, NO, and CO emissions are analyzed and measured for various ammonia addition (0–41 % by weight) percentages, equivalence ratio of 1.0, and heat inputs of 17 & 21 kW for 10 PPI and a combination of 10 and 20 PPI porous foams. A preheated air stream coming from the annular zone speeds up fuel dissociation and helps in stabilizing the flame on the upstream side of the combustor. Combustor exit temperatures are lower in sandwich cases of 10 + 20 PPI than the porous foams of 10 PPI. However, with porous foams of 10 PPI, the air preheat temperature is higher. The insertion of porous foams shows better recirculation of heat and stable combustion is observed for higher percentages of ammonia and higher thermal inputs. The OH radicals are distributed for larger areas inside the dumb combustor, while for porous combustion, it is distributed near the porous foams. The porous sandwich cases of 10 + 20 PPI shows higher combustion efficiency compared to 10 PPI and without porous cases. The chemical kinetic analysis shows that the HNO and HCO radicals act as the main intermediate channel for NO and CO production.

Identification of the simplest sugar-like molecule glycolaldehyde towards the hot molecular core G358.93–0.03 MM1

ABSTRACT Glycolaldehyde (CH2OHCHO) is the simplest monosaccharide sugar in the interstellar medium, and it is directly involved in the origin of life via the ‘RNA world’ hypothesis. We present the first detection of CH2OHCHO towards the hot molecular core G358.93–0.03 MM1 using the Atacama Large Millimetre/Submillimetre Array (ALMA). The calculated column density of CH2OHCHO towards G358.93–0.03 MM1 is (1.52 ± 0.9) × 1016 cm−2 with an excitation temperature of 300 ± 68.5 K. The derived fractional abundance of CH2OHCHO with respect to H2 is (4.90 ± 2.92) × 10−9, which is consistent with that estimated by existing two-phase warm-up chemical models. We discuss the possible formation pathways of CH2OHCHO within the context of hot molecular cores and hot corinos and find that CH2OHCHO is likely formed via the reactions of radical HCO and radical CH2OH on the grain-surface of G358.93–0.03 MM1.

Photophysical oxidation of HCHO produces HO2 radicals.

Formaldehyde, HCHO, is the highest-volume carbonyl in the atmosphere. It absorbs sunlight at wavelengths shorter than 330 nm and photolyses to form H and HCO radicals, which then react with O2 to form HO2. Here we show HCHO has an additional HO2 formation pathway. At photolysis energies below the energetic threshold for radical formation we directly detect HO2 at low pressures by cavity ring-down spectroscopy and indirectly detect HO2 at 1 bar by Fourier-transform infrared spectroscopy end-product analysis. Supported by electronic structure theory and master equation simulations, we attribute this HO2 to photophysical oxidation (PPO): photoexcited HCHO relaxes non-radiatively to the ground electronic state where the far-from-equilibrium, vibrationally activated HCHO molecules react with thermal O2. PPO is likely to be a general mechanism in tropospheric chemistry and, unlike photolysis, PPO will increase with increasing O2 pressure.

Combustion of biomass pyrolysis gas: Roles of radiation reabsorption and water content

Biomass energy has drawn increased attention owing to its zero carbon emissions and large reserves. Pyrolysis instead of direct combustion is an efficient and clean way for biomass energy conversion. As a strong radiative species, H2O greatly affects the combustion processes. Despite the large concentration and fluctuation of H2O content in biomass pyrolysis gases (py-gas), radiation reabsorption effect has not been systematically investigated for py-gas combustion. In this study, one-dimensional simulations of premixed py-gas/air flames were conducted, using PREMIX code with both adiabatic and radiative models. The effects of H2O content and radiation reabsorption were examined. As H2O content in the py-gas mixture increased from 40% to 50%, the flame speeds decreased from 42.86 to 28.08 cm/s, while the relative differences caused by radiation reabsorption increased from 9.92% to 17.42%. Radiation reabsorption affected laminar flame speed primarily through the preheat-induced chemical effect, which was mainly controlled by HCO radical. The outlet mole fraction of NO was reduced by up to 13.56% when radiation reabsorption was considered. Reaction pathway analyses revealed that the NO emission was closely related to the outlet temperature and the peak NCO concentration, which were the limiting factors for the thermal-NO route and the fuel-NO route, respectively.

Effects of EGR on combustion and emission characteristics of PODE/methanol RCCI mode at high load

In order to extend the high-load operation range of polyoxymethylene dimethyl ethers (PODE)/methanol dual-fuel reactivity controlled compression ignition (RCCI) combustion mode, a numerical model of in-cylinder combustion was established by coupling PODE/methanol chemical reaction kinetics with CONVERGE software. And then the influence mechanism of exhaust gas recirculation (EGR) addition on in-cylinder combustion process, combustion stability and pollutant formation of the RCCI engine under high load and pilot injection strategy were investigated. The results show that with the increase of EGR ratio, the peak values of the first heat release formed by PODE pilot injection combustion and in-cylinder pressure decrease, the combustion start timing and CA50 phase are gradually delayed. While the peak value of the second heat release formed by PODE main injection combustion at low EGR ratio and the combustion duration remain unchanged. Meanwhile, as the EGR ratio increases from 0 to 30 %, the brake thermal efficiency (BTE) decreases from 46.54 % to 44.40 %. And the in-cylinder equivalent ratio and temperature field distributions become uniform, and both high-temperature region (above 1800 K) and NOx generation area are reduced, which decreases NOx emissions by 42.6 % without increasing soot emissions. The methanol mixture at squish zone is subjected to the high-temperature and high-pressure of pilot injection combustion, resulting in obvious pressure oscillation. While EGR addition decreases the generation of HCO and OH active radicals, ignition points and reaction rate, which effectively inhibits methanol spontaneous combustion and knock phenomenon, and decreases the ringing intensity from 2.82 MW/m2 to 1.50 MW/m2. The pilot injection strategy coupled with 18 % EGR can extend the indicated mean effective pressure to 1.22 MPa. However, the load further extension is mainly limited by the sharp decline of BTE.

Role of CH2O moiety on laminar burning velocities of oxymethylene ethers (OMEn): A case study of dimethyl ether, OME1 and OME2

Oxymethylene ethers (OMEn) are an important family of e-fuels that can be produced sustainably from carbon dioxide and hydrogen via renewable electricity. In this work, laminar flame propagation of dimethyl ether (DME, which can be deemed as OME0), dimethoxymethane (OME1) and methoxy(methoxymethoxy)methane (OME2) was investigated in a constant-volume cylindrical combustion vessel. Laminar burning velocities (LBVs) of the three fuels were derived at 423 K, 1–10 atm and equivalence ratios of 0.7–1.5. A kinetic model for the high-temperature oxidation of the three fuels was developed with the isomerization and decomposition reactions of OME2 radicals theoretically calculated. Reasonable predictions can be achieved by the present model during the validation against the new data in this work and previous data in literature. Based on the modeling analysis, fuel-specific flame chemistry of the three fuels was analyzed, especially for the key formation pathways of major intermediates including formaldehyde, methyl formate and CH3. Special attentions were paid on the role of CH2O moiety, which is demonstrated by the variation of LBV and flame chemistry with the ratio (α) of CH2O moiety to the rest moiety in the fuel molecule (α = 1, 2 and 3 for DME, OME1 and OME2). It is observed from the experimental and simulated results that as α increases, the LBV profile has close peak values and peaks towards rich conditions, which results in the crossings of profiles and ascending LBV values under the richest conditions. Reactions involving fuel-specific radicals HCO and CH3 result in the peak shift of H profile and different LBV values, especially under the richest conditions. Furthermore, extended α values at 0 and ∞ by using methane and formaldehyde respectively were also explored with kinetic modeling to provide more insight into the effects of fuel molecular structures.

Automated identification and calculation of prompt effects in kinetic mechanisms using statistical models

The kinetics of prompt dissociation involves rovibrationally excited species (generally formed by exothermic reactions) which may dissociate or isomerize prior to thermalization via collisions with the bath gas. Treating such rovibrationally excited species (so-called “hot” species) with standard kinetic phenomenology may result in incorrect macroscopic representation of their reactivity. This work presents the first fully automated methodology for the calculation of prompt effects of a chosen species in a kinetic mechanism, including (i) reaction selection; (ii) theoretical calculation of rate constants and prompt branching fractions; and (iii) final rate constant fitting. The energy partition between hot fragments is estimated using a variety of statistical models, including a new physically sound microcanonical statistical model based on the rovibrational density of states of the fragments. The methodology is validated against literature data for the prompt dissociations of HCO and C3H7 radicals. The microcanonical statistical model is in better agreement with trajectory simulations for larger species and is thus applicable for practical systems that typically involve large molecules, for which direct dynamics calculations are impractical. The automated workflow is applied to the evaluation of the effects of prompt dissociation for two isomeric radicals C4H71-3 (1-methylallyl) and C4H71-4 (3-buten-1-yl). Twelve H-atom abstraction reactions are selected and the corresponding rate constants are computed with first principles theory. The microcanonical statistical model predicts that prompt dissociations of C4H71-3 and C4H71-4 are already significant at 1000 K, resulting in differences of up to an order of magnitude at 2000 K with respect to the phenomenological thermal rate constants. To illustrate the effects of prompt dissociation on simulations of experimental data, the calculated prompt rate constants are implemented in both CRECK and C3MechV3.3 kinetic mechanisms. Simulations of experimental flame data illustrate the noticeable impact of prompt dissociation kinetics on the high-temperature combustion reactivity of C4H8-1 and C4H8-2.

Theoretical study on the mechanism and kinetics of the oxidation of allyl radical with atomic and molecular oxygen

The C3H5O and C3H5O2 potential energy surfaces accessed by the oxidation reactions of allyl radical with atomic and molecular oxygen have been mapped out at the CCSD(T)-F12b/cc-pVTZ-F12//ωB97XD/6-311G(d,p) level of electronic structure theory to unravel the reaction mechanism. Temperature- and pressure-dependent reaction rate constants have been evaluated using variable reaction coordinate transition state and RRKM-Master Equation theoretical kinetics methods. The C3H5 + O reaction is found to be fast in the 300-2500 K temperature interval, with the total rate constant of 1.8-1.0 × 10−10 cm3 molecules s−1 independent of pressure in the considered 30 Torr – 100 atm range. Acrolein + H formed by a simple O addition/H elimination mechanism via the CH2CHCH2O association complex are predicted to be the major reaction products with the branching ratio decreasing from 61% at 300 K to 44% at 2500 K. Other substantial bimolecular products include C2H3 + formaldehyde (32%-26%) formed through the C-C bond β-scission in CH2CHCH2O and two minor products C2H4 + formyl radical HCO and allene + OH, where the latter, formed via direct H abstraction by O from the central carbon atom of allyl, becomes significant only at high temperatures above ∼1500 K. The C3H5 + O2 reaction studied in the 200-2500 K temperature range shows a peculiar kinetic behavior characteristic for a bimolecular reaction with a low entrance barrier, shallow association well, and high ensuing isomerization and decomposition barriers to bimolecular products. This behavior is described in terms of three distinct temperature regimes: the low-temperature one with slightly negative dependence of the rate constant, the intermediate one where the rate constant sharply drops, and the high-temperature regime with an Arrhenius-like rate constant. The rate constant is relatively high (10−13-10−12 cm3 molecule−1 s−1) in the low-temperature regime when the reaction produces the peroxy association complex CH2CHCH2OO, but slow at higher temperatures when it leads to bimolecular products. Under combustion relevant conditions, the C3H5 + O2 rate constant is by 5 to 3 orders of magnitude lower than that for C3H5 + O, but since O2 concentrations in flames could be as much as 3 orders of magnitude larger than O concentrations, C3H5 + O2 cannot be ruled out as a significant allyl radical sink. Above 1500 K, the C3H5 + O2 reaction can form vinoxy radical + formaldehyde (40%-15%) via the five- or four-membered ring closure and opening mechanism starting from the initial peroxy intermediate, acrolein + OH (41%-49%) via the H shift from the attacked carbon to the terminal oxygen followed by the immediate O-O bond cleavage, and allene + OH (18-25%) via the H migration from the central CH group to the terminal O atom accompanied or followed by the C-O bond rupture. Modified Arrhenius expressions fitting the computed rate constants for both reactions have been generated and proposed for kinetic models.

Experimental and Theoretical Investigation of Reactions of Formyl (HCO) Radicals in the Gas Phase: (I) Kinetics of HCO Radicals with Ethyl Formate and Ethyl Acetate in Tropospherically Relevant Conditions.

Formyl (HCO) radicals were generated in situ in the gas phase via the photolysis of glyoxal in N2 at 248 nm using the pulsed laser photolysis-cavity ring-down spectrometry technique, and the absorption cross-section of the radical was measured to be σHCO = (5.3 ± 0.9) × 10-19 cm2 molecule-1 at 298 K and 615.75 nm, which was the probing wavelength. The kinetics of the reactions of HCO radicals with ethyl formate (EF) and ethyl acetate (EA) were investigated experimentally in the temperature range of 260-360 (±2) K at a pressure of 60 Torr/N2. The absolute rate coefficient for the reaction between HCO and EF was measured to be (298 K) = (1.39 ± 0.30) × 10-14 cm3 molecule-1 s-1 at ambient temperature, whereas that for the reaction of HCO with EA was measured tobe (298 K) = (2.05 ± 0.43) × 10-14 cm3 molecule-1 s-1. The reaction of HCO with EA was faster than that with EF, which might be due to the greater stability of the formed radical intermediate due to hyperconjugative and inductive effects. The dependency of the measured kinetics on experimental pressures and laser fluences was examined within a certain range. To complement the experiments, kinetics of the title reactions in the temperature range of 200-400 K were deciphered theoretically via the canonical variational transition-state theory with small-curvature tunneling and interpolated single-point energy (CVT/SCT/ISPE) method using a dual-level approach at the CCSD(T)/cc-pVTZ//MP2/6-311++G(d,p) level of theory/basis set. A good degree of agreement was detected between the rate coefficients measured experimentally and those calculated theoretically both at room temperature and throughout the range of temperatures studied. The kinetic branching ratios and thermochemistry of the reactions were investigated to understand the thermodynamic feasibility and kinetic lability of each pathway throughout the studied temperatures. Atmospheric implications of these reactions of HCO radicals are also discussed.

Research on the Effect of Water Injection Pressure on Knocking Combustion of a Direct Injection Gasoline Engine

In this study, the research method of numerical simulation is used to explore the inhibition of different water injection pressures on knock combustion of turbocharged direct injection gasoline (GDI) engines by coupling computational fluid dynamics with a chemical-kinetics model. First, the ignition advance angle and compression ratio are increased to induce the GDI engine to knock, and then the influence of the water injection pressure on the in-cylinder, evaporation of water, and the knock of the gasoline engine are analyzed. The simulation results show that, compared with no water injection, the direct injection of water in the cylinder can significantly reduce the knock intensity. When the water injection pressure is greater than 40 bar, the knock intensity is less than 2 and the knocking is completely suppressed. In this work, the effects of different water injection pressures on knocking are explored by analyzing the effects of water injection pressure on water atomization, in-cylinder combustion, and the knocking mechanism. On the one hand, the evaporation rate of water increases with increasing water injection pressure and the quality of the liquid film generally improves. On the other hand, direct water injection can significantly reduce the distribution of CH2O in the end mixture, thereby reducing the generation of H2O2 and further suppressing the spontaneous combustion of the end mixture. At the moment of knock, when the water injection pressure is greater than 40 bar, the detonation mechanism of the no. 7 monitoring point does not produce a sudden change in HCO radicals. The water spray can effectively reduce the NOx emission, and the NOx emission under the water spray pressure of 120 bar is the lowest. However, after spraying water, it will increase CO emissions.

Methanediol CH2(OH)2 and hydroxymethyl CH2OH+: key organic intermediates on the path to complex organic molecules

Context. Ab initio molecular dynamics simulations were carried out to study the formation pathways to complex organic molecules when a OH+ projectile hit an interstellar dust grain covered only by methanol molecules. The selected target material is a methanol cluster formed by ten units (CH3OH)10. Aims. The focus of this paper is the process where methanediol CH2(OH)2 and hydroxymethyl CH2OH+, both key organic intermediate molecules, were involved in the formation mechanisms of stable complex organic molecules (COMs). Methods. We performed Born-Oppenheimer (ab initio) molecular dynamics (BOMD) simulations under the hybrid functional of Head-Gordon ωB97X-D. We used the initial kinetic impact energy of 10, 12, 15, 18, 20, and 22 eV. Results. We corroborate that CH2(OH)2 and CH2OH+ are the main precursors to form molecules such as methoxymethanol CH3OCH2OH, the formyl radical HCO, the Criegee biradical CH2OO, and formaldehyde H2Co and its elusive HCOH isomer. We discuss the mechanism formation of these complex organic molecules. We compare the formation pathways with previous theoretical results where both key intermediates are present. The pathways in some cases go through CH2(OH)2 or undergo by CH2OH+. Conclusions. We confirm that CH2(OH)2 and CH2OH+ play a key role on the path to the formation of abundant H2CO. These mechanisms can give insight into alternative pathways relevant to understanding experimental processes with key steps within those precursors.

Effect of port water injection on suppressing knock in gasoline direct injection engines

AbstractThe effect of different port water injection (PWI) ratios on the knock in gasoline direct injection engines is explored. First, a simulation study is carried out under knock conditions to explore the time and location of the knock and the chemical mechanism that causes it. Second, water injection amount to 10%, 20%, 30%, and 40% are set to explore the effects of different water injection ratios on knocking. The influence of the different water injection ratios on the chemical mechanism of knocking is evaluated and that of the chemical mechanism on the in‐cylinder temperature and the impact of heat release rate (HRR) is explored. The results show that PWI can effectively reduce the occurrence of spontaneous combustion in the cylinder by reducing the flame propagation speed. On one hand, the changes in the low‐temperature reaction substances CH2O and HRR tend to be consistent and the peaks of CH2O and HRR move back with the increase in water injection. So, different ratios of PWI can affect the flame propagation speed by affecting the generation and consumption of CH2O, OH radicals, and HCO radicals. Also, PWI can significantly reduce the generation of in‐cylinder OH radicals, ultimately suppressing the generation of the high‐temperature stage. In addition, PWI can effectively reduce the mean temperature and mean pressure. Compared to other water injection ratios, a 30% water injection ratio is the most effective at inhibiting knocking. At this time, the knocking intensity is the lowest, and the cycle power reaches its maximum of 1120 J.

Modelling the Radical Chemistry on Ice Surfaces: An Integrated Quantum Chemical and Experimental Approach

Heterogeneous radical processes on ice surfaces play a vital role in the formation of building blocks of the biologically relevant molecules in space. Therefore, quantitative mechanistic details of the radical binding and radical reactions on ices are crucial in rationalizing the chemical evolution in the Universe. The radical chemistry on ice surfaces was explored at low temperatures by combining quantum chemical calculations and laboratory experiments. A range of binding energies was observed for OH, HCO, CH3, and CH3O radicals binding on ices. Computed reaction paths of the radical reactions on ices, OCS + H and PH3 + D, explained the experimentally observed products. In both radical reactions, quantum tunnelling plays a key role in achieving the reactions at low temperatures. Our findings give quantitative insights into radical chemistry on ice surfaces in interstellar space and the planetary atmospheres.

Atomistic simulations of syngas oxy-combustion in supercritical CO2

The growing energy demand worldwide is currently supplied by the direct use of fossil fuels, which are limited in nature and represent an environmental concern. Syngas/oxy-combustion technologies have become popular due to recent advances in carbon capture and storage and the possibility to avoid NOX formation by replacing N2 with supercritical CO2. However, the successful implementation of these systems faces several drawbacks: variability in syngas composition and lack of understanding of the chemical kinetics at elevated temperature and pressures in the presence of CO2. In this work, we carried out a molecular dynamics study of syngas oxy-combustion using ReaxFF force field. Three main initiation reactions were identified: H2 + O2 → HO2 + H, H2 → H + H, and CO2 → CO + O, with the last being dominant at high temperatures and high concentrations of CO2. We also found that increasing the initial CO2 concentration and decreasing that of O2 delays ignition. However, for enriched CO2 mixtures, this substrate exerts a catalytic effect in the reactions H2 → H + H and H2O → OH + H by forming the intermediate HCO2. In the absence of initial CO2, formyl radical (HCO) chemistry is lacking due to the prominent consumption of H species by molecular oxygen via O2 + H → OH + O and H + O2 (+M) → HO2 (+M). However, we observed the association between HCO and OH radicals to form stable formic acid, a reaction not implemented in syngas mechanisms.

H/D isotope effect observed in the isotropic Fermi contact interaction of formyl radical: Experimental and theoretical analysis of the inter- and intra-molecular dynamics

An unexpected deficit of the computed hyper fine coupling constant in normal formyl HCO radicals, compared to that expected based on the proton to deuteron gyromagnetic ratio of the DCO species, was observed in experimental electron paramagnetic resonance studies of HCO and DCO radicals in a CO solid matrix at cryogenic conditions. Still, the matrix was found to have only a small effect on the anisotropic parts of the magnetic parameter tensors. The underlying isotope effect between the lighter proton and the heavier deuteron on the motional dynamics was verified and elucidated by quantum chemical calculations. The experimental results obtained within a temperature range of 1.4 K–4.2 K require special attention due to the tunneling motions of the molecule and its constituent particles. The effect from vibrational, rotational, and librational motion observed in the molecular states of formyl as a probe, averaged over the dynamics of the low temperature CO matrix isolation, reveals a clear proton isotope effect under both classical and quantum conditions.

EGR rate 변화에 따른 바이오디젤 정적 연소 특성에 관한 수치해석 연구

This paper was conducted to investigate the effect of EGR on the combustion characteristics, NO<SUB>X</SUB> and CO formation characteristics of constant volume combustion of the biodiesel fuel. To achieve this, methyl decanoate, methyl 9 decenoate, and n-heptane species were applied for the simulation of the biodiesel and diesel chemical reactions during the constant volume combustion process. The analysis of biodiesel-EGR combustion was performed by simultaneously considering the mole fraction which was composed of the N₂, H₂O, CO₂, and O₂ species according to the EGR rate (10~60%). As a result of the combustion characteristics, the maximum OH radical was reduced as the EGR rate increase, and the ignition delay was increased at the same time. Most of NO<SUB>X</SUB> emission was generated by the thermal NO<SUB>X</SUB> reaction, and it was not emitted after the EGR rate of 30% conditions due to the decrease of combustion temperature and oxygen concentration. The reactivity of CO generation was showed the high absolute rate of production in the reaction path related to the reactions of HCO radical, and it has a trade-off relationship with the tendency of NO<SUB>X</SUB> emissions. In addition, it was indicated that the UHC emission increased rapidly since the chemical reactions related to the fuel oxidation did not occur actively when the ambient temperature was 800~1,000 K and the EGR rate was 60% conditions.

Formation pathways of complex organic molecules: OH• projectile colliding with methanol ice mantle (CH3OH)10

In this article, we simulated the collisions of an OH• projectile impacting on a methanol cluster formed by ten units of methanol to mimic an ice mantle (CH3OH)10. The chemical processes occurring after the impact were studied through Born-Oppenheimer (ab-initio) molecular dynamics. We focus on collisions with initial kinetic impact energy of 10–22 eV, where the richest chemistry happens. We report the formation mechanisms of stable complex organic molecules (COMs) such as methoxymethanol CH3OCH2OH, formic acid HCOOH, formyl radical HCO, formaldehyde H2CO and its elusive HCOH isomer. We show that CH2(OH)2, •CH2OH or +CH2OH are key intermediates to generate H2CO and other COMs. We compare the outcomes using OH• with those using OH− projectiles. These processes are likely relevant to the production of COMs in astrophysical environments. We discuss its formation mechanism and the astrophysical implications of these chemical pathways in star-forming regions.

Interaction of the HCO radical with molecular hydrogen: Ab initio potential energy surface and scattering calculations.

The potential energy surface describing the interaction of the HCO radical with molecular hydrogen has been computed through explicitly correlated coupled cluster calculations including single, double, and (perturbative) triple excitations [RCCSD(T)-F12a], with the assumption of fixed molecular geometries. The computed points were fit to an analytical form suitable for time-independent quantum scattering calculations of rotationally inelastic cross sections and rate coefficients. Since the spin-rotation splittings in HCO are small, cross sections for fine-structure resolved transitions are computed with electron-spin free T matrix elements through the recoupling technique usually employed to determine hyperfine-resolved cross sections. Both spin-free and fine-structure resolved state-to-state cross sections for rotationally inelastic transitions are presented and discussed.