Infrared spectrum of the CH3OCH2 radical in solid argon

The methoxymethyl radical, CH(3)OCH(2), is prepared via hydrogen photodissociation from dimethyl ether during codeposition of CH(3)OCH(3) in excess argon at 4 K with laser-excited metal plume radiation. The spectrum of this radical is characterized by four infrared absorptions at 1468.1, 1253.9, 1226.6, and 944.4 cm(-1), which are assigned by deuterium substitution as well as frequency and intensity calculations using density functional theory. The O-CH(2) bond length is calculated to be 0.07 ? shorter than the CH(3)-O bond due to additional π bonding interactions. In the matrix near-UV irradiation destroys the CH(3)OCH(2) radical with the formation of HCO radical and CH(4), which is different from the decomposition mechanism of CH(3)OCH(2) radical to H(2)CO and CH(3) radical proposed for the gas phase process.     

Unimolecular dissociation of the CH3OCO radical: an intermediate in the CH3O + CO reaction

This work investigates the unimolecular dissociation of the methoxycarbonyl, CH(3)OCO, radical. Photolysis of methyl chloroformate at 193 nm produces nascent CH(3)OCO radicals with a distribution of internal energies, determined by the velocities of the momentum-matched Cl atoms, that spans the theoretically predicted barriers to the CH(3)O + CO and CH(3) + CO(2) product channels. Both electronic ground- and excited-state radicals undergo competitive dissociation to both product channels. The experimental product branching to CH(3) + CO(2) from the ground-state radical, about 70%, is orders of magnitude larger than Rice-Ramsperger-Kassel-Marcus (RRKM)-predicted branching, suggesting that previously calculated barriers to the CH(3)OCO --> CH(3) + CO(2) reaction are dramatically in error. Our electronic structure calculations reveal that the cis conformer of the transition state leading to the CH(3) + CO(2) product channel has a much lower barrier than the trans transition state. RRKM calculations using this cis transition state give product branching in agreement with the experimental branching. The data also suggest that our experiments produce a low-lying excited state of the CH(3)OCO radical and give an upper limit to its adiabatic excitation energy of 55 kcal/mol.     

CH3S与CO反应机理的理论研究

在G3(MP2)//B3LYP/6-311 G(d,p)水平上,对CH3S自由基与CO气相反应的微观机理进行了理论研究.结果表明:该反应共存在3个反应通道,产物分别为CH3 OCS,CH2S HCO和CH2S HOC.由于形成产物CH3 OCS的活化势垒较低,因此为主要反应通道,这与实验观察到的结果是一致的.     

CoII Cryptates Convert CO2 into CO and CH4 under Visible Light

Three Co^II octaazacryptates, with different substituents on the aromatic rings (Br, NO₂, CCH), were synthesised and characterised. These and the already published non-substituted cryptate catalysed CO₂ photoreduction to CO and CH₄ under blue visible light at room temperature. Although CO was observed after short irradiation times and a large range of catalyst concentrations, CH₄ was only observed after longer irradiation periods, such as 30 h, but with a small catalyst concentration (25 nm ). Experiments with ¹³C labelled CO₂ showed that CO is formed and reacts further when the reaction time is long. The CCH catalyst is deactivated faster than the others and the more efficient catalyst for CH₄ production is the one with Br. This reactivity trend was explained by an energy decomposition analysis based on DFT calculations.     

Theoretical study on the reaction mechanism of (CH3)3CO(.) radical with NO

The reaction mechanism of (CH3)3CO(.) radical with NO is theoretically investigated at the B3LYP/6-31G* level. The results show that the reaction is multi-channel in the single state and triplet state. The potential energy surfaces of reaction paths in the single state are lower than that in the triple state. The balance reaction: (CH3)3CONO←→ (CH3)3CO(.)+NO, whose potential energy surface is the lowest in all the reaction paths, makes the probability of measuring (CH3)3CO(.) radical increase. So NO may be considered as a stabilizing reagent for the (CH3)3CO(.)radical.     

First experimental observation on different ionic states of the tert-butoxy [(CH3)3CO*] radical

A continuous tert-butoxy (CH3)+CO* radical beam is produced in situ by respective pyrolysis of both (CH3)3CONO at 115(+/-0.5) degrees C and (CH3)3COOC(CH3)3 at 87(+/- 0.5) degrees C. By combining the HeI photoelectron (PE) spectrum with the improved density function theory (DFT) calculations, we have concluded that the (CH3)3CO* radical has C3V symmetry and X2E ground state. The study does not only provide the ionization energies of different ionic states of the (CH3)3CO* radical for the first time, but also the first example in which there have been similar vibrational structures in different ionic states caused by removal of the electron on an orbital. It is also pointed out that (CH3)3CONO is a good source for obtaining the (CH3)3CO* radical beam, and that NO is a stable regent for the active radical. The results will promote the studies in electron spin resonance (ESR) research on the mechanisms of both the initiation of the formation of a new radical and the radical-chain polymerization in which the (CH3)3CO* radical participates.     

Millimeter wave spectrum of bromomethyl radical, CH2Br

The rotational spectra of the two isotopic species of the bromomethyl radical, CH2 79Br and CH2 81Br, have been observed in their ground electronic state 2B1 in the 180-470 GHz frequency region, corresponding to a-type transitions from N=8-7 to N=21-20. The radical was produced by hydrogen abstraction of methylbromide (CH3Br) either by chlorine or by fluorine atoms in a free space cell. Hyperfine structure due to the bromine nucleus has been resolved in the observed spectra, and the rotational constants as well as the fine and hyperfine interaction constants were accurately determined for both isotopomers. The inertial defect was determined to be 0.028 96(20) and 0.028 95(20) amu A(2), for CH2 79Br and CH2 81Br, respectively, suggesting a planar structure. By fixing the [angle]HCH bond angle at 124.5 degrees , an effective molecular structure can be derived as r0(CBr)=1.848 A and r0(CH)=1.084 A. A comparison of the molecular structure of various halogen-substituted methyl radicals with respect to the planarity of these radicals is discussed.     

Theoretical study of stabling function of the NO to the (CH3)3CO · radical

The stabling function of the NO to the (CH₃)₃CO · radical has been theoretically investigated. Density functional theory (DFT) calculations are performed to optimize the geometries of relevant species. The single‐point energy is evaluated at CCSD(T)/6‐31++G** level. Three reaction channels of (CH₃)₃CO · + NO in the singlet state are considered. The calculations indicate that NO is a stable reagent of active radical (CH₃)₃CO. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Visible absorption spectra of the phenothiazine radical cation and its 10-substituted derivatives

The visible absorption spectra for the phenothiazine radical cation and its 10-substituted derivatives (the substituents were methyl, phenyl, benzyl and cyclohexyl), generated electrochemically in acetonitrile solutions, are reported. Substituent effects on these spectra are considered in the frame of quantum chemical calculations using the MNDO method.

---

VIS-Absorptionsspektren des Phenothiazinradikal-Kations und seiner 10-substituierten Derivate (Kurze Mitteilung)

Zusammenfassung Die Absorptionsspektren des elektrochemisch generierten Phenothiazinradikal-Kations und seiner 10-substituierten Derivate (Methyl, Phenyl, Benzyl und Cyclohexyl als Substituenten) wurden im sichtbaren Bereich vermessen. Die Substituenteneffekte werden im Rahmen der quantenchemischen MNDO-Methode diskutiert.

     

The UV absorption spectrum of trimethylsilyl radical in the gas phase

The UV absorption spectrum of trimethylsilyl radical was observed at 256 nm for the first time by photolysing allyltrimethylsilane and hexamethyldisilane with an ArF excimer laser. A bimolecular rate constant for recombination of trimethylsilyl radical of (2.5±0.5×10⁻¹¹ molecule⁻¹ cm³ s⁻¹ was measured.     

Theoretical study on the kinetics of OH radical reactions with CH3OOH and CH3CH2OOH

The mechanisms and kinetics studies of the OH radical with alkyl hydroperoxides CH(3)OOH and CH(3)CH(2)OOH reactions have been carried out theoretically. The geometries and frequencies of all the stationary points are calculated at the UBHandHLYP/6-311G(d,p) level, and the energy profiles are further refined by interpolated single-point energies method at the MC-QCISD level of theory. For two reactions, five H-abstraction channels are found and five products (CH(3)OO, CH(2)OOH, CH(3)CH(2)OO, CH(2)CH(2)OOH, and CH(3)CHOOH) are produced during the above processes. The rate constants for the CH(3)OOH/CH(3)CH(2)OOH + OH reactions are corrected by canonical variational transition state theory within 250-1500 K, and the small-curvature tunneling is included. The total rate constants are evaluated from the sum of the individual rate constants and the branching ratios are in good agreement with the experimental data. The Arrhenius expressions for the reactions are obtained.     

Dissociation of acetone radical cation (CH3COCH3(+*) --> CH3CO(+) + CH3(*)): an ab initio direct classical trajectory study of the energy dependence of the branching ratio

The nonstatistical dissociation of acetone radical cation has been studied by ab initio direct classical trajectory calculations at the MP2/6-31G(d) level of theory. A bond additivity correction has been used to improve the MP2 potential energy surface (BAC-MP2). The energy dependence of the branching ratio, dissociation kinetics, and translational energy distribution for the two types of methyl groups have been investigated using microcanonical ensembles and specific mode excitation. In each case, the dissociation favors the loss of the newly formed methyl group, in agreement with the experiments. For microcanonical ensembles, the branching ratios for methyl loss are calculated to be 1.43, 1.88, 1.70, and 1.50 for 1, 2, 10, and 18 kcal/mol of excess energy, respectively. The energy dependence of the branching ratio is seen more dramatically in the excitation of individual modes involving C-C-O bending. For modes 3 and 6, the branching ratio rises to 1.6 and 1.8-2.3 when 1 or 2 kcal/mol are added, respectively, but falls off when more energy is added. For mode 8, the branching ratio continues to rise monotonically from 1.5 to 2.76 when 1-8 kcal/mol of excess energy are added.     

Theoretical study on the reaction mechanism of(CH_3)_3CO+CO

The global environment pollution includes pho-tochemical smog, acid rain and stratospheric ozonedepletion. The short-lived species/radicals in atmos-phere are closely related to these phenomena. Theshort-lived species/radicals bring the photochemicalsmog,…     

High-resolution discrete absorption spectrum of alpha-methallyl free radical in the vapor phase

The alpha-methallyl free radical is formed in the flash photolysis of 3-methylbut-1-ene, and cis-pent-2-ene in the vapor phase, and then subsequent reactions have been investigated by kinetic spectroscopy and gas-liquid chromatography. The photolysis flash was of short duration and it was possible to follow the kinetics of the radicals' decay, which occurred predominantly by bimolecular recombination. The measured rate constant for the alpha-methallyl recombination was (3.5+/-0.3) x 10(10) mol(-1) ls(-1) at 295+/-2K. The absolute extinction coefficients of the alpha-methallyl radical are calculated from the optical densities of the absorption bands. Detailed analysis of related absorption bands and lifetime measurements in the original alpha-methallyl high-resolution discrete absorption spectrum image were also carried out by image processing techniques.     

The electronic absorption spectrum of the CNO free radical in the gas phase

A new band with heads at 796.3.3 and 7893.1 A has been found during the flash photolysis of 3-methyl-4-oximinoisoxazol-5(411)-one. By comparison with earlier work in a neon matrix. and on the basis of a partial rotational analysis, the band is assigned as the 0 0 band of the A²x⁺-X²11_i transition of the CNO free radical. Preliminary mlecular constant are given.     

The hyperfine structure of electron spin resonance spectrum of tricobalt cluster radical anion CH3CCo3(CO)

CH₃CCo₃(CO)₉ was synthesized from the reaction between chloralose and Co₂(CO)₈. The radical anion was generated by electrochemical reduction, and electron spin resonance spectra in THF were recorded by in situ electrolysis in the sample tube in the ESR cavity at 298 and 110K with the spectral data <g> =2.015, g =2.013, g =2.016; <a> = —35.2G, a₁ = —78.6G and a =—13.5G. The effect on shift of the magnetic resonance field by using the second order perturbation theory was discussed, and the electron spin density on Co atom orbitals 4s, 4p and 3d was calculated, respectively to be 4s: —0.08, 3d: 0.855 and 4p: 0.225.     

Absolute rate constants for F + CH3CHO and CH3CO + O2, relative rate study of CH3CO + NO,and the product distribution of the F + CH3CHO reaction

Using a pulse-radiolysis transient UV–VIS absorption system, rate constants for the reactions of F atoms with CH₃CHO (1) and CH₃CO radicals with O₂ (2) and NO (3) at 295 K and 1000 mbar total pressure of SF₆ was determined to be k₁=(1.4±0.2)×10⁻¹⁰, k₂=(4.4±0.7)×10⁻¹², and k₃=(2.4±0.7)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹. By monitoring the formation of CH₃C(O)O₂ radicals (λ>250nm) and NO₂ (λ=400.5nm) following radiolysis of SF₆/CH₃CHO/O₂ and SF₆/CH₃CHO/O₂/NO mixtures, respectively, it was deduced that reaction of F atoms with CH₃CHO gives (65±9)% CH₃CO and (35±9)% HC(O)CH₂ radicals. Finally, the data obtained here suggest that decomposition of HC(O)CH₂O radicals via C C bond scission occurs at a rate of <4.7×10⁵ s⁻¹. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 913–921, 1998     

Thermal decomposition of CH3I using I-atom absorption

The recently developed I-atom atomic resonance absorption spectrometric (ARAS) technique has been used to study the thermal decomposition kinetics of CH₃I over the temperature range, 1052–1820 K. Measured rate constants for CH₃I(+Kr)→CH₃+I(+Kr) between 1052 and 1616 K are best expressed by k(±36%)=4.36×10⁻⁹ exp(−19858 K/T) cm³ molecule⁻¹ s⁻¹. Two unimolecular theoretical approaches were used to rationalize the data. The more extensive method, RRKM analysis, indicates that the dissociation rates are effectively second-order, i.e., the magnitude is 61–82% of the low-pressure-limit rate constants over 1052–1616 K and 102–828 torr. With the known E₀=ΔH₀⁰=55.5 kcal mole ⁻¹, the optimized RRKM fit to the ARAS data requires (ΔE)_down=590 cm⁻¹. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 535–543, 1997.