Vibrational Distribution Research Articles

Catechin and Epicatechin. What’s the More Reactive?

Catechin and epicatechin are two isomeric flavonoids. Despite the vital properties highlighted by numerous scientific studies, very little data is available on the intrinsic reactivity of these compounds. To provide more details on the stability and reactivity of catechin and epicatechin, this study is performed by means of theoretical calculation methods. For this purpose, geometry optimizations and frequency calculations at the B3LYP/6-31 + G (d, p) level of theory has been carried out and Natural Bond Orbital (NBO) analysis and VEDA (Vibrational Energy Distribution Analysis). The geometric and energy parameters and NBO analysis show that catechin appears more stable than epicatechin. The hydroxyl group position on the ring C of the catechol structure represents a factor that influences this relative stability. The global and local reactivity parameters reveal that epicatechin becomes more reactive than catechin. They indicate that their hydroxyl groups correspond to their most receptive sites. Fukui indices, VEDA and acidity study establish that O28–H29 remains the most reactive.

Non-adiabatic couplings induced complex-forming mechanism in H+MgH+ → Mg++H2 reaction

A chemical process may involve multiple adiabatic electronic states, and non-adiabatic couplings play an important role in the reaction mechanism. In this work, the effect of non-adiabatic couplings in the H+MgH+ → Mg+ + H2 reaction are studied using the time-dependent wave packet method and trajectory surface hopping method. The calculated results show that the reaction follows a direct abstraction process when the non-adiabatic couplings are neglected. However, when non-adiabatic couplings are included in the calculations, a long-lived excited state complex (MgH2+)* can be formed during the reaction. These direct and complex-forming reaction pathways are revealed by trajectory surface hopping calculations. The non-adiabatic couplings induced complex-forming mechanism not only increases the reactivity but also has significant effect on the product vibrational state distribution.

Quantum resonances and roaming dynamics in formaldehyde photodissociation.

The unimolecular dissociation of formaldehyde is studied via excitation to the à band at several excitation energies from just below the ground state radical dissociation threshold to 5000 cm-1 above it. CO product rotational distributions, photofragment excitation spectroscopy and state-correlated slice imaging results are combined with quasi-classical trajectory calculations to reveal manifestations of quantum effects in this complex dissociation process involving interactions among radical, molecular, and roaming pathways. Evidence of nodal structure at the tight transition state to molecular products is investigated and correlations between the CO rotational and H2 vibrational distributions are used to suggest the transition state modes that are responsible. A large modulation of the roaming yield previously identified and associated with roaming resonances at the onset of the H + HCO(v1,v2,v3 = 0,0,0) product channel suggests a similar origin for enhanced roaming and a roaming yield that is strongly dependent on parent rotation on the 2641 band just 15 cm-1 above the H + HCO(0,2,1) threshold. Similar resonances are predicted on other bands that share near coincident energies with HCO product vibrational thresholds.

Development of a real-time vibration imager to visualize vibration distribution at all frequencies

Development of a real-time vibration imager to visualize vibration distribution at all frequencies

Transmission of Haptic Experience by a Bracelet-type Tactile Device to Reproduce Vibration Distribution

Recently, the demand for technology to remotely transmit haptic experiences related to skills has been increasing. This study attempts to convey a haptic experience with tactile sensation by reproducing the spatial patterns of vibrations generated at the wrist using a bracelet device with multiple sensors and vibrators. This paper investigates the human discrimination capability of haptic experiences during different whisking motions by comparing the bracelet device with a conventional tool-mounted device. We also investigate the effect of the ISM method, which can modulate the waveform to lower frequencies while maintaining the original sensation. The results indicated that reproduction of spatial distribution by bracelet device improves discrimination of differences in the rotation direction, and ISM further improves the discrimination of directional rotation compared to the raw signals.

Structure Activity Relationship, Topological Analysis and Molecular Docking Analysis of Pharmaceutical Molecule 2356 -Tetrafluoro-4-Pyridine Carbonitrile

The theoretical vibrational spectral features of 2,3,5,6 Tetrafluoro-4-pyridinecarbonitrile were explored and compared with experimental results. The geometrical parameters, vibrational wavenumbers, bonding features and Energies were calculated at the B3LYP level with the basis set 6-311++G(d,p) levels. The calculated wavenumbers, vibrational energy distribution Analysis (VEDA), potential energy distributions (PEDs), and vibrational spectra were used to suggest reliable vibrational assignments. Molecular Electrostatic Potential investigations revealed the reactive zones around the molecule. The computed HOMO-LUMO energies were -8.369 and -3.380 eV, respectively, indicating charge transfer inside the molecule. The charge transfer of charge due to intra molecule interactions has been explained using naturalbond orbital analysis. The ELF and LOL calculations were provide a visual aid for interpreting the results of electronic structure. The molecular docking approach was used to find the optimal ligand–protein orientation using the ligand 2,3,5,6 Tetrafluoro-4 pyridinecarbonitrile, which was docked with five distinct proteins. The main aim of the present study is to evaluate the biological activity of the selected compound using theoretical calculations.

2D IR spectra of the intrinsic vibrational probes of ionic liquid from dispersion corrected DFT-MD simulations

We present the vibrational spectral profile of the intrinsic cationic (N-H) and anionic (C-O) probe stretch modes in methylammonium formate (MAF) using first principles molecular dynamics simulations in conjunction with the density functional theory (DFT) approaches. All simulations were performed employing Becke-Lee-Yang-Parr (BLYP) and Perdew-Burke-Ernzerhof (PBE) functionals, using three types of van der Waals (vdW) dispersion-corrected representations (D2, D3, and dispersion-corrected atom-centered one-electron potentials) and two values of plane-wave cut-off (300 and 600 Ry). The long-range electrostatic interactions, directional hydrogen bonds and non-directional van der Waals (vdW) dispersion forces are required to accurately interpret the interionic interactions in the protic ionic liquid, MAF. We compute the 2D IR correlation spectra from the wavelet-derived instantaneous frequencies obtained at each timeframe applying the cumulant expansion truncated at the second order to measure the dynamics of vibrational spectral diffusion. Here, we investigate the effects of electronic structure parameters on the spectral bands of the 2D IR contour plot. The spectral bands for both the N-H and CO stretching vibrations attain a round shape by 1 ps, indicating the loss of frequency correlation irrespective of the type of BLYP or PBE-based functionals. Further, the diagonal linewidth of the 2D IR spectral band agrees with the FWHM (full width at half maxima) of the calculated normalized vibrational stretch frequency distribution. Moreover, this study also finds the reason behind the coalescence of the symmetric and antisymmetric C-O stretches in the computed 2D IR spectra. Besides, these computational results may attract the attention of the experimental spectroscopists as it provides molecular-level interpretation and detailed ultrafast time-resolved spectral information of the intrinsic stretching vibrations and associated dynamics of the protic ionic liquid (PIL). Herein, we inspect the quality of different density functionals along with vdW dispersion corrections. However, even though the experimental data is not available for direct comparison of the results, we finally conclude that the inclusion of the effects of dispersion interactions provides a better estimation of the spectroscopic properties.

Isotope effect of rovibrational distribution of hydrogen molecules desorbed from amorphous carbon

When the hydrogen isotope atom is injected into the amorphous carbon with the incident energies E in of 20, 50, and 80 eV, we obtain the following physical quantities of hydrogen isotope atoms/molecules emitted from the amorphous carbon using molecular dynamics and heat conduction hybrid simulation. The physical quantities are the time evolution of the emission rate, the depth distribution of the original location of the hydrogen emitted from the target, the polar angular dependence, and the translational, rotational, and vibrational energy distributions. In addition, the approximate analysis yields the emission distributions at the vibrational (v) and rotational (J) levels. Using these distributions, we evaluate the rotational temperature T rot for v = 0 and small J states. From the above, it is found that molecules with higher rotational levels J tend to be emitted as E in increases or as the mass of hydrogen isotope increases. Moreover, the isotope effect appears in the mass dependence of T rot.

State-to-state quantum dynamical study of H + Br2 → HBr + Br reaction

The time-dependent wave packet method has been employed to calculate the state-to-state integral cross sections and differential cross sections (DCSs) for three initial states of the title reaction on the recently constructed neural network potential energy surface. It is found that the product HBr(υ′ = 2, 3, 4) states have the dominated population in the entire energy region considered here, indicating an inverted HBr vibrational state distribution. More than half of the available energy ends up as product internal motion, and most of which goes into the vibrational motion. Our calculations show that initial rotational excitation of Br2 has little effect on the product ro-vibrational state distributions and DCSs of the reaction. While the initial vibrational excitation has some influences. The initial vibrational excitation to υ0 = 5 obviously enhance the product vibrational excitation in the low energy region. The DCSs for collision energy up to 0.5 eV at the ground and rotationally excited state are peaked in the backward direction, but the width of the angular distribution increases considerably with the increase of collision energy. For the vibrationally excited state, the DCSs are rather complicated with some strong forward scattering peaks for highly vibrationally excited products.

Investigation of In Situ Vibration During Wire and Arc Additive Manufacturing.

Wire and arc additive manufacturing (WAAM) is becoming a promising technique due to its high deposition rate and low cost. However, WAAM faces challenges of coarse grains. In this study, a novel in situ vibration method was proposed to suppress these imperfections of WAAM. Temperature and vibration distributions were explored first, and the optimized parameters were utilized for manufacturing low-carbon steel parts. The results revealed that after the vibration, the average grain size in fine grain zone was reduced from 9.8 to 7.1 μm, and that in coarse grain zone was declined from 10.6 to 7.4 μm, respectively. No large deformation occurred due to the low temperature. Grain refining was attributed to more dendrite fragments induced by excessive stress at the roots of dendrites. The refined grains enhanced mechanical strength of the parts in both X and Z directions and improved the average hardness. After the vibration, the ultimate tensile strength and yield strength were increased to 522.5 and 395 MPa, which represented an increase of 10% and 13.8%, respectively. The average hardness was improved to 163 HV, which was an increase of 10.1%.

A previously unknown cyclic alkanolamine and molecular ranking using the pair distribution function

A new six-membered cyclic alkanolamine with chemical formula C6H15N3O3 was synthesized by the reaction of glycolaldehyde with gaseous ammonia. The molecular structure, characterized by a hexagonal ring of alternating carbon and nitrogen atoms with three hydroxymethyl groups attached to the carbon atoms, could not be unambiguously determined by elemental analysis and 1H/13C/15N NMR. The molecular structure and conformation were further determined using a combination of vibrational spectroscopy (IR and Raman) and real-space pair distribution function (PDF) analysis. The crystal structure was determined ab initio from laboratory X-ray powder diffraction (XRPD) with orthorhombic space group Ama2 (No. 40) and unit-cell parameters a = 12.1054 (2) Å, b = 13.5537 (2) Å and c = 5.20741 (8) Å. Consistent structure models could be obtained by symmetry-independent PDF and PDF-Rietveld co-refinements. Independent local structure refinements indicate that the most likely deviations from the average structure consist of small tilting and translational distortions of hydrogen-bonded molecular stacks. Thermal analysis (TG/DTA) and temperature-dependent XRPD measurements were also performed to determine the thermal behavior.

Experimental and computational investigation on spectroscopic characterization, molecular modeling and biological evaluation of 3, 3′, 4′7-tetrahydroxyflavone, 3, 3′, 4′7-tetrahydroxyflavone-6-methoxymethane against in A549 cells

The Molecular structural, vibrational, frequencies electronic and potential energy distribution of 3, 3′ , 4′7-tetrahydroxyflavone and 3′, 4′7-tetrahydroxyflavone-6-methoxymethane molecules have been carried out using the techniques of FT-IR and FT-Raman spectra with the aid of computational calculations and compared with experimental calculations. The electronic properties, such as highest occupied molecular orbital and the lowest unoccupied molecular orbital energy levels, molecular electrostatic potential and atomic charges analysis were performed at above levels. The correlation graphs of observed versus calculated vibrational frequencies were plotted and density functional theory gave better wavenumber agreement than others. Molecular docking study show that the intermolecular hydrogen-bonding interactions and binding free energy of -8.4 kcal/mol and -8.1 kcal/mol between 3THDFN and 6THDFN with 1AO6 protein were reported and this study supported the in designing structure-based Human Serum Albumin (HSA) receptors may be of significant biological and pharmaceutical importance. In additional, the in vitro cytotoxicity of compounds confirms the anticancer activity against human lung cancer cell lines was assessed in 24-h tetrazoliumbromide-dye (MTT) cytotoxicity assays. Hence, the present investigations pave the way for the development of lung cancer drugs (A549).

Coherent wave reflection in integrable or chaotic symmetrical acoustical billiards

This study is concerned with the distribution of flexural vibrations in plates excited with a Gaussian white noise. The distribution of energy can be characterized by its homogeneity and isotropy. Some particular geometries like the Bunimovitch stadium generate a field that is both homogeneous and isotropic. But other geometries produce a field that is homogeneous but not isotropic (like the rectangle panel) or non-isotropic and not homogeneous (like the circular panel). It is known that these features drive the establishment of diffuse field. However, in the present work, we show that even at high frequency and for these three particular geometries, the diffuse field cannot be reached rigorously. Owing to symmetries, the vibrational response is always enhanced on some particular lines and points by the effect of coherence between rays. The enhancement factors are predicted theoretically with the image-source method. The presence of energy enhancement is also shown experimentally by measuring the vibrational energy density in the 20 Hz–4 kHz frequency range for these three plates excited with a random white noise. Measurement of enhancement factors shows a good agreement with their theoretical predictions.

Synthesis of Schiff base (E)-4-((2-hydroxy-3,5-diiodobenzylidene)amino)-N-thiazole-2-yl)benzenesulfonamide with antimicrobial potential, structural features, experimental biological screening and quantum mechanical studies

We report the synthesis and characterisation of the Schiff base (E)-4-((2-hydroxy-3,5-diiodobenzylidene)amino)-N-thiazole-2-yl) benzene sulfonamide (DITH) prepared the by condensation of 3,5-diiodosalicylaldehyde and sulfathiazole. The synthesised compound was characterised with spectral techniques like FTIR, 1HNMR and UV-Visible spectroscopy. The molecule was optimised using computational methods employing DFT/B3LYP/cc-pVDZ/Lanldz(I) basis sets followed by the simulation of the vibrational spectra, scaled and compared with experimental spectra for vibrational assignment and potential energy distribution. The 1HNMR calculated from the standard GIAO method with DMSO as a solvent was also compared with experimental spectra. The UV-Vis spectrum calculated using TD-DFT/CAM-B3LYP/cc-pVDZ/Lanl2dz(I). Wave function based properties like localised orbital locator, electron localisation function and non-covalent interactions has been studied extensively. The compound DITH's pharmacodynamic indicated that the compound has excellent drug-likeness properties. Prediction of the activity and structure spectra (PASS) studies predicted that it has anti-infective properties, confirmed by a docking score of -7.1 and -7.2 kcal/mol for antibacterial and antifungal properties. Experimental studies show that the newly synthesised Schiff base shows significant inhibition of bacteria and fungi growth compared to standard drugs.

Spatial distribution of vibration and damage of high rock slope under blast loading

The safety of the high rock slope under blasting loading is of great concern during the engineering construction. A better understanding of vibration distribution and reasonable monitoring scheme are essential to control the dynamic response induced by blasting excavation of high rock slope. Based on the excavation of WuDongde high rock slope in southwest of China, vibration amplification characteristic around the slope surface was investigated carefully with different kinds of experiment. The Peak Particle Velocity (PPV) of blasting vibration at the slope surface and flat ground was compared. Results demonstrate that the PPV at the slope surface is large than that of flat ground and the amplification effect is obvious. The partial amplification law of slope surface is revealed as the amplification factor of vibration at the outside of the berm is much larger than that of inside. The amplification effect in the vertical direction is stronger than the radial and tangential direction. Then numerical simulation was employed to investigate the vibration amplification characteristic with more working conditions. Results agree well with the experiment and reveal that the local amplification characteristic could be obviously found around the berm. The blasting energy, geometry of the bench and rock mass quality could affect the amplification effect significantly. The suggestion of blasting vibration monitoring scheme for high rock slope was proposed according to different objectives based the understanding of vibration amplification. If the aim is to evaluate the dynamic stability or get the blasting vibration attenuation law of high rock slope, monitoring points should be arranged at the inside of the berm, but while the most unfavorable response of rock mass is expected to be obtained, the out edge of the berm should be selected as the monitoring position. The study expects to provide a good reference for the blasting vibration control and measurement of high rock slope.

Zero-dimensional and pseudo-one-dimensional models of atmospheric-pressure plasma jets in binary and ternary mixtures of oxygen and nitrogen with helium background

A zero-dimensional (volume-averaged) and a pseudo-one-dimensional plug-flow (spatially resolved) model are developed to investigate atmospheric-pressure plasma jets operated with He, He/O2, He/N2 and He/N2/O2 mixtures. The models are coupled with the Boltzmann equation under the two-term approximation to self-consistently calculate the electron energy distribution function. An agreement is obtained between the zero-dimensional model calculations and the spatially averaged values of the plug-flow simulation results. The zero-dimensional model calculations are verified against spatially resolved simulation results and validated against a wide variety of measurement data from the literature. The nitric oxide (NO) concentration is thoroughly characterized for a variation of the gas mixture ratio, helium flow rate and absorbed power. An ‘effective’ and a hypothetical larger rate coefficient value for the reactive quenching are used to estimate the role of the species N2(A3Σ, B3Π; v > 0) and multiple higher N2 electronically excited states instead of only N2(A3Σ, B3Π; v = 0) in this quenching. The NO concentration measurements at low power are better and almost identically captured by the simulations using the ‘effective’ and hypothetical values, respectively. Furthermore, the density measurements under the same operation conditions are also better predicted by the simulations adopting these values. It is found that the contribution of the vibrationally excited nitrogen molecules N2(v ⩾ 13) to the net NO formation rate gains more significance at higher power. The vibrational distribution functions (VDFs) of molecular oxygen O2(v < 41) and nitrogen N2(v < 58) are investigated regarding their formation mechanisms and their responses to the variation of operation parameters. It is observed that the N2 VDF shows a stronger response than the O2 VDF. The sensitivity of the simulation results with respect to a variation of the VDF resolutions, wall reaction probabilities and synthetic air impurity levels is presented. The simulated plasma properties are sensitive to the variation, especially for a feed gas mixture containing nitrogen. The plug-flow model is validated against one-dimensional experimental data in the gas flow direction, and it is only used in case an analysis of the spatially resolved plasma properties inside the jet chamber is of interest. The increasing NO spatial concentration in the gas flow direction is saturated at a relatively high power. A stationary O2 VDF is obtained along the direction of the mass flow, while a continuously growing N2 VDF is observed until the jet nozzle.

Ab Initio Direct Dynamics.

The reactivity and dynamics of molecular systems can be explored computationally by classical trajectory calculations. The traditional approach involves fitting a functional form of a potential energy surface (PES) to the energies from a large number of electronic structure calculations and then integrating numerous trajectories on this fitted PES to model the molecular dynamics. The ever-decreasing cost of computing and continuing advances in computational chemistry software have made it possible to use electronic structure calculations directly in molecular dynamics simulations without first having to construct a fitted PES. In this "on-the-fly" approach, every time the energy and its derivatives are needed for the integration of the equations of motion, they are obtained directly from quantum chemical calculations. This approach started to become practical in the mid-1990s as a result of increased availability of inexpensive computer resources and improved computational chemistry software. The application of direct dynamics calculations has grown rapidly over the last 25 years and would require a lengthy review article. The present Account is limited to some of our contributions to methods development and various applications. To improve the efficiency of direct dynamics calculations, we developed a Hessian-based predictor-corrector algorithm for integrating classical trajectories. Hessian updating made this even more efficient. This approach was also used to improve algorithms for following the steepest descent reaction paths. For larger molecular systems, we developed an extended Lagrangian approach in which the electronic structure is propagated along with the molecular structure. Strong field chemistry is a rapidly growing area, and to improve the accuracy of molecular dynamics in intense laser fields, we included the time-varying electric field in a novel predictor-corrector trajectory integration algorithm. Since intense laser fields can excite and ionize molecules, we extended our studies to include electron dynamics. Specifically, we developed code for time-dependent configuration interaction electron dynamics to simulate strong field ionization by intense laser pulses. Our initial application of ab initio direct dynamics in 1994 was to CH2O → H2 + CO; the calculated vibrational distributions in the products were in very good agreement with experiment. In the intervening years, we have used direct dynamics to explore energy partitioning in various dissociation reactions, unimolecular dissociations yielding three fragments, reactions with branching after the transition state, nonstatistical dynamics of chemically activated molecules, dynamics of molecular fragmentation by intense infrared laser pulses, selective activation of specific dissociation channels by aligned intense infrared laser fields, angular dependence of strong field ionization, and simulation of sequential double ionization.

Novel bisthiazole ligand and its copper(II) complex with unusual seven membered ring: Synthesis, characterization, experimental and theoretical study of the effect of ligand flexibility, and antimicrobial activity

In the search of antimicrobial agents a novel bisthiazole ligand containing a methylamine linker (ethyl 2-((2-methylthiazole-4-yl)methylamino)thiazole-4-carboxylate (BTa) and its copper(II) complex [CuCl2BTa]·2H2O were synthetized. Both compounds were characterized by analytical and spectroscopic methods. Single crystal X-ray diffraction of copper complex evidence a pentacoordinated copper(II) center of intermediate geometry forming 5 and 7 membered chelate rings with BTa acting as a tridentate ligand leaving the amine NH group in the thiazole linker available for participation in intermolecular interactions. Structure packing was analyzed by means of Hirshfeld surfaces, 2D fingerprint plots and lattice interaction energies were assessed. In order to deepen the understanding of the coordination to the flexible ligand DFT studies were carried out at the B3LYP/LANL2DZ level of theory. Calculated FTIR frequencies were used to perform a Vibrational Energy Distribution Analysis (VEDA) where potential energy distribution of vibrational was determined. Minimum inhibitory concentrations for BTa and CuBTa on E. coli ATCC 25922, S. aureus ATCC 25923, P. aeruginosa ATCC 9027 and C. albicans ATCC 10231 were determined.

Vibrational mode-specificity in the dynamics of the Cl + C2H6 → HCl + C2H5 reaction.

We report a detailed dynamics study on the mode-specificity of the Cl + C2H6 → HCl + C2H5 H-abstraction reaction. We perform quasi-classical trajectory simulations using a recently developed high-level ab initio full-dimensional potential energy surface by exciting five different vibrational modes of ethane at four collision energies. We find that all the studied vibrational excitations, except that of the CC-stretching mode, clearly promote the title reaction, and the vibrational enhancements are consistent with the predictions of the Sudden Vector Projection (SVP) model, with the largest effect caused by the CH-stretching excitations. Intramolecular vibrational redistribution is also monitored for the differently excited ethane molecule. Our results indicate that the mechanism of the reaction changes with increasing collision energy, with no mode-specificity at high energies. The initial translational energy mostly converts into product recoil, while a significant part of the excess vibrational energy remains in the ethyl radical. An interesting competition between translational and vibrational energies is observed for the HCl vibrational distribution: the effect of exciting the low-frequency ethane modes, having small SVP values, is suppressed by translational excitation, whereas a part of the excess vibrational energy pumped into the CH-stretching modes (larger SVP values) efficiently flows into the HCl vibration.

Dynamics of Reaction CH3CHI + O2 Investigated via Infrared Emission of Products CO, CO2, and OH.

The reaction CH3CHI + O2 has been commonly employed in laboratories to produce a methyl-substituted Criegee intermediate CH3CHOO, but the detailed dynamics of this reaction remain unexplored. We carried out this reaction by irradiating a flowing mixture of CH3CHI2 (∼70 mTorr) and O2 (∼4 and 8 Torr) at 308 or 248 nm and observed infrared emission of the products with a step-scan Fourier-transform spectrometer. Upon irradiation at 248 nm with O2 ∼4 Torr, a Boltzmann distribution of CO (v ≤ 4, J ≤ 25) with average vibrational energy (12 ± 2) kJ mol-1 and of OH (v = 1, J ≤ 5.5) were observed and assigned to be produced from the decomposition of CH3C(O)OH* to form CO + CH3OH and OH + CH3CO, respectively. The observed broadband emission of CO2 was simulated with two vibrational distributions of average energies (42 ± 3) and (114 ± 6) kJ mol-1 and assigned to be produced from the decomposition of CH3C(O)OH* and (methyl dioxirane)*, respectively. The results upon irradiation of the sample at 308 nm are similar, likely indicating a small fraction of energy partition into these products and rapid thermalization of CH3CHI*. Compared with reaction CH2I + O2, the title reaction yielded products with much less internal excitation, consistent with the expectation that these observed products receive much less fraction of available energy upon fragmentation when an additional methyl moiety was present in the parent. The large-v component of CO observed in experiments of CH2I + O2 at 248 nm, produced from secondary reaction HCO + O2, was absent in this work because the corresponding secondary reaction CH3CO + O2 in decomposition of CH3CHOO* produces α-lactone + OH or H2CO + CO + OH.