Laser Magnetic Resonance Detection Research Articles

Does the HO2 radical react with H2S, CH3SH, and CH3SCH3?

AbstractThe kinetics of the title reactions were investigated in a discharge flow tube by using laser magnetic resonance detection of HO2. The upper limits for the bimolecular rate constants for the reactions of HO2 with H2S (k1), CH3SH (k2), and CH3SCH3 (k3) are <3 × 10−15, <4 × 10−15, and <5 × 10−15 cm3 molecule−1 s−1, respectively, at 298 K. Our upper limit for k1 is three orders of magnitude lower than the previously reported value.Measurements at higher temperatures also yield similar upper limits. Our results suggest that HO2 is not an important oxidant for these reduced compounds in the atmosphere. © 1994 John Wiley & Sons, Inc.

Kinetics of the Reaction HOCO + O2 in the Gas Phase

Using the discharge flow method, the kinetics of the gas phase reactionHOCO + O2 products (1)was investigated at room temperature and pressures around p ≈ 2.0 mbar with Far Infrared LaserMagnetic Resonance (FIR-LMR) detection of HOCO, HO2 , and OH. From the measured concentration-versus-time decay profiles of HOCO in the absence and presence of a large excess of O2 , theoverall rate constant of the reaction was found to bek1 (296 K) = (9.9 ±1.5) • 1011 cm3/mol • s.The main reaction channel, which leads to production of HO2 + CO2 , could be established.

Kinetics of the reactions of carbene (CH2) (X3B1) with selected polycyclic aromatic hydrocarbons at temperatures between 296 and 690 K

The kinetics of the reactions of CH 2 radicals in their X~ 3 B 1 ground electronic state with the aromatic hydrocarbon molecules benzene (1), naphthalene (2), phenanthrene (3), anthracene (4), and biphenyl (5) have been studied. Experimental measurements were carried out for reactions 2-5 at temperatures between 445 and 690 K using an isothermal discharge flow system with far-infrared laser magnetic resonance (FIR-LMR) detection of the CH 2 radicals. The results of these investigations as well as those of an earlier study of the rate constant of reaction 1 in the temperature range 296 K≤T≤683 K were analyzed in light of recent temperature-dependent data on the competing reactions of CH 2 (a 1 A 1 )

Fast Flow Kinetic Studies of the Reaction CH2OH + HCl ⇋ CH3OH + Cl. The Heat of Formation of Hydroxymethyl

AbstractThe kinetics of the chlorination equilibrium of methanol, CH2OH + HCl ⇋ CH3OH + Cl (1, – 1), have been studied using the fast flow technique with Laser Magnetic Resonance and Electron Paramagnetic Resonance detection. The rate constants of the forward and reverse reactions were found to be k1 = (2.3±0.9) ·1011 exp [‐(20.9±2.9) kJ·mol−1/RT] cm3/mol·s in the temperature range 500 K≤T≤812 K and k‐1 = (3.7±0.4)±1013 cm3/mol·s at room temperature. These kinetic results were utilized in third law and second law procedures to obtain the value of the heat of formation of the hydroxymethyl radical. The entropy of CH2OH, S0f,298(CH2OH) = (254±4) J/mol·K, and the activation energy of reaction (‐1), E‐1 = (0±4) kJ/mol, which are required for the calculations, were selected by critical assessment of the available literature data. The average of the third law and second law determinations provided SfH0298(CH2OH) = ‐(9±6) kJ/mol. This value is higher by 17 kJ/mol than the heat of formation value in common use and implies a stronger C – H bond energy in methanol, D298(H–CH2OH) = 410 kJ/mol. These new thermochemical quantities are in excellent agreement with the very recent recommendations of Seetula and Gutman [J. Phys. Chem. 96, 5401 (1992)] and have important implications for modeling studies of complex chemical systems such as the combustion of methanol.

Rate Constants for the Reactions of CH2 (X̄3B1) with Selected Alkenes at Temperatures Between 296 K≤T≤728 K

AbstractThe kinetics of the reactions of CH2 (X̄3B1) with selected alkenes R = ethylene (1), tetramethylethylene (2), cycloheptatriene (3), and 1,3‐butadiene (4) were studied at temperatures between 296 K≤T≤728 K. Rate constants were measured for reactions (2–4) using the discharge flow technique with Far‐Infrared Laser Magnetic Resonance (FIR–LMR) detection of 3CH2. The experimental data can be described by the rate expressions (±2σ)magnified image These data and results for reaction (1) obtained earlier were analyzed to separate the contributions to the CH2 (X̄) depletion by reactive channels versus collisional excitation to the ã1A1 state of CH2 followed by reactions of CH2 (ã). The rate expressions (±2σ) for the reactive pathways of CH2 (X̄) were found to be magnified image.

Investigations of the reaction between CH2(X̃3B1) and O2 in the temperature range 233 K ≤ T ≤ 433 K

AbstractThe reaction between CH2(X̃T3B1) radicals (3CH2) and O23CH2+O2→products,has been studied in a discharge flow reactor with Laser Magnetic Resonance (LMR) detection of 3CH2 and OH radicals and Electron Spin Resonance detection of O and H atoms. From the measured concentration‐versus‐time profiles of [3CH2] in the absence and presence of a large excess of O2 the overall rate coefficient of the reaction was found to bemagnified imageIn the temperature range 233 K ≤ T ≤ 433 K. A limit for the contribution of H atom forming reaction channels of <20% was determined. The results are discussed in relation to available literature data on the formation of stable products. Main reaction channels leading directly to production of CO + H2O and H2 + CO2 are concluded to be of importance.

Kinetics of the Reactions of CH2(X̃3B1) with HCl and HBr

AbstractThe reactions of CH2(X̃3B1) with HCl (1) and HBr (2) have been studied in an isothermal discharge flow system. CH2 radicals were generated via the reactions of O atoms with a large excess of CH2CO. Their concentration‐versus‐time profiles were measured under pseudo first‐order conditions using Laser Magnetic Resonance (LMR) detection. The rate coefficients of reactions (1) and (2) were found to be kexp1 = (1.7 ± 0.3) · 1012 · exp [–(436 ± 45) K/T] cm3/mol · s in the temperature range 296 K ≤ T ≤ 670 K and k2 = (6.9 ± 1.4) · 1012 cm3/mol · s at T = 296 K. CH3 + Cl or Br, respectively, are suggested to account for the main reaction products.

ChemInform Abstract: Kinetics and Mechanism of the OH + HO2 Reaction

Abstractare studied by using a low‐pressure discharge flow reactor with combined laser magnetic resonance and resonance fluorescence detection of atoms and molecules.

Kinetics and mechanism of the hydroxyl + hydroperoxo reaction

A discharge flow reactor with laser magnetic resonance and resonance fluorescence detection axes is used to measure the rate constant for the reaction of OH and HO{sub 2} radicals by measuring the decay of OH in excess HO{sub 2} under pseudo-first-order conditions. Particular care is taken to reduce impurity O and H atoms to low levels since their presence leads to an underestimate of the rate constant. The rate constant is measured to be (8.0{sup +3.0}{sub {minus}2.0}) {times} 10{sup {minus}11} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} at 298 K and 2 Torr after a small (3%) correction is made for the impurity atoms. It is argued that recent experimental and theoretical results indicate that the reaction mechanism is likely dominated by attack at the hydrogen end of HO{sub 2} and that the reaction is unusually fast due a long-range attractive interaction.

The reaction of CH2(X̄3B1) with C6H6

AbstractThe kinetics of the reaction CH2(X̄3B1) + C6H6 → products (1) has been studied in a discharge flow reactor using Laser Magnetic Resonance (LMR) detection for CH2. The experiments yielded the overall rate constant kexp1 = (4.7 ± 2.4) · 10t3 exp(−(37.5 ± 2.4) kJ mol−1/RT) in the temperature range 448 K ≦T ≦ 683 K. The product formation was investigated for reaction (1) as well as the corresponding reaction CH2(ã1A1) + C6H6 → products (2) in a stationary photolysis reactor employing gas chromatographic analysis by photolyzing mixtures of CH2CO and C6H6 at λ1 = 366 nm and λ2 = 313 nm. The relative yields of the products cycloheptatriene (CHT) and toluene (T) were found to depend on the wavelength, [T]/([CHT] + [T]) = (0.13 ± 0.02) and (0.23 ± 0.02) at λ1, and λ2, respectively. The implications of these results and the mechanisms are discussed.

Primary products of the reaction between O(3P)-atoms and C2H4 studied with ESR- and LMR-detection

The primary products of the reaction between O(3P)-atoms and C2H4 O(3P)+C2H4→products (1) have been studied at room temperature in the gas phase. The products in the low pressure regime were investigated in two isothermal discharge flow systems with Electron Spin Resonance (ESR) detection of O- and H-atoms and Far Infrared Laser Magnetic Resonance (LMR) detection of O-atoms and HCO- as well as CH2-radicals. The absolute concentrations of these species were determined using several independent titration reactions. The experiments yielded the branching ratios for the following reaction channels: O+C2H4→C2H3O+H k1a/k1=(0.50±0.10) (1a) O+C2H4→CH3+HCO k1b/k1=(0.44±0.15) (1b) O+C2H4→CH2+H2CO k1c/k1=(0.06±0.03) (1c) The formation of the high pressure stabilization products ethylene oxide and acetaldehyde from the reaction channels O+C2H4+M→C2H4O+M (1d) O+C2H4+M→CH3CHO+M (1e) was observed in a static system at pressures between 5 bar ≦p≦70 bar using Hg*-sensitized decomposition of N2O as the O-atom source and gaschromatographic analysis. From the half pressure for CH3CHO production the lifetime of the addition complex from O+C2H4 with respect to redissociation and dissociation into fragments is concluded to be of the order 10−11 s. Thus, 1.2 H-atom migration in the addition complex has to proceed on this time scale.

ChemInform Abstract: Kinetic Studies of the Reactions of HSO with NO2, NO, and O2.

A far-infrared rotational transition in HSO has been observed by using an optically pumped laser magnetic resonance (LMR) spectrometer. LMR detection of HSO was utilized to study the reactions of HSO with NO/sub 2/, NO, and O/sub 2/. Rate coefficients were measured under pseudo-first-order conditions in a discharge flow system coupled to the spectrometer. The results are k(HSO + NO/sub 2/) = (9.6 +/- 2.4) x 10/sup -12/ cm/sup 3/ molecule/sup -1/ s/sup -1/; k(HSO + NO) less than or equal to 1 x 10/sup -15/ cm/sup 3/ molecule/sup -1/ s/sup -1/; and k(HSO + O/sub 2/) less than or equal to 2 x 10/sup -17/ cm/sup 3/ molecule/sup -1/ s/sup -1/. All measurements were made at low pressure (1-5 Torr) and room temperature (296 +/- 3 K). Experiments were also conducted to determine the products of the HSO + NO/sub 2/ reaction. The results show that a species is produced which reacts with O/sub 2/ to form HO/sub 2/ with a rate coefficient of (3 +/- 2) x 10/sup -13/ cm/sup 3/ molecule/sup -1/ s/sup -1/ which was determined from the rate of HO/sub 2/ formation. They propose that the unidentified intermediate is HSO/sub 2/.

ChemInform Abstract: A Kinetic Study of the Reaction of HO2 with Ozone

Abstractis performed using a discharge‐flow system with laser magnetic resonance detection.

Kinetic studies of the reactions of mercaptooxy with nitrogen dioxide, nitric oxide, and oxygen

A far-infrared rotational transition in HSO has been observed by using an optically pumped laser magnetic resonance (LMR) spectrometer. LMR detection of HSO was utilized to study the reactions of HSO with NO/sub 2/, NO, and O/sub 2/. Rate coefficients were measured under pseudo-first-order conditions in a discharge flow system coupled to the spectrometer. The results are k(HSO + NO/sub 2/) = (9.6 +/- 2.4) x 10/sup -12/ cm/sup 3/ molecule/sup -1/ s/sup -1/; k(HSO + NO) less than or equal to 1 x 10/sup -15/ cm/sup 3/ molecule/sup -1/ s/sup -1/; and k(HSO + O/sub 2/) less than or equal to 2 x 10/sup -17/ cm/sup 3/ molecule/sup -1/ s/sup -1/. All measurements were made at low pressure (1-5 Torr) and room temperature (296 +/- 3 K). Experiments were also conducted to determine the products of the HSO + NO/sub 2/ reaction. The results show that a species is produced which reacts with O/sub 2/ to form HO/sub 2/ with a rate coefficient of (3 +/- 2) x 10/sup -13/ cm/sup 3/ molecule/sup -1/ s/sup -1/ which was determined from the rate of HO/sub 2/ formation. They propose that the unidentified intermediate is HSO/sub 2/.

Kinetic study of the reaction of HO2 with ozone

The reaction HO2+O3→OH+2O2 has been studied using a discharge-flow system with laser magnetic resonance detection. The rate constant for the reaction was determined directly by monitoring the first-order decay of isotopically labeled H18O2 in excess 16O3. The data give a curved Arrhenius plot over the temperature range 243<T<413 K: k(T)=(3.8±2.4) ×10−14 exp[−(820±190/T)] cm3 s−1. A more representative fit is obtained with a three parameter expression: k(T)=(3.2±5.8)×10−13 exp[−(1730±740)/T] + (1.2±0.5)×10−15 cm3 s1. The error limits are the 95% confidence limits on the coefficients while the accuracy of the measurements is estimated to be about ±20% at each temperature. An analysis of the OH radical product indicates that 16OH is formed predominately (75±10)%. The scrambling reactions H18O2+16O3→H16O2+18O18O16O (1c) and H18O2+16O2→H16O2+18O2 (8) were also examined and found to be slow. Their rate constants are k1c<2×10−17 cm3 s−1 at 297 and 333 K and k8<3×10−17 cm3 s−1 at 297 and 413 K.

Comparative Study of the Reactions of 16OH and 18OH with H16O2.

The gas phase reactions 18OH + H16O2 → H2 18O + 16O2 (1a) 18OH + H16O2 → 16OH + H18O16O (1b) were studied at room temperature in a discharge flow reactor with far infrared laser magnetic resonance (LMR) detection of 16OH, 18OH and H16O16O. The formation of 16OH in the course of the reaction was observed. The absolute rate constant for the overall removal of 18OH in excess of H16O16O was determined. Each run was accompanied by a control experiment replacing the initial 18OH by the same amount of 16OH. From these experiments a branching ratio is obtained of k1a/( k1a + k1b) = 0.52 ± 0.08

Direct Measurements of the Isotope Exchange Reactions between 18OH and NO, NO2, N2O and O2

The isotope exchange reactions between 18OH and NO, NO2, N2O and O2 were studied at room temperature in a discharge flow system with laser magnetic resonance detection of 18OH and 16OH. Exchange rate constants of where obtained for NO and NO2, respectively. Upper limits of k < 1 · 108 cm3/mol s can be reported for the reactions The results are compared with recombination rate data in the limit of high pressures and with vibrational deactivation measurements.

Far infrared laser magnetic resonance detection of NH and ND (a 1Δ)

Rotational spectra of the excited a 1Δ state of NH and ND have been observed by far infrared laser magnetic resonance spectroscopy. For ND(a 1Δ) the spectroscopic constants are B0=264 750.263(30) MHz, D0=14.383 83(91) MHz, aN =109.63(22) MHz, aD =11.03(23) MHz, eqQ(N)=−4.0(15) MHz, gr=−0.000 86(10), and gL =1.000 506(17). For NH (a 1Δ), the constants are B0=493 043.182(95) MHz, D0=50.453 MHz (constrained in fit), aN =109.65(85) MHz, aH =70.9(14) MHz, eqQ(N)=−4.0 MHz (constrained in fit), gr =−0.001 58(6), and gL =1.001 03 (constrained in fit). Aspects of the electronic structure of the radical as revealed by the magnetic hyperfine constants are discussed in relation to those of chemically similar systems. The Zeeman parameters are interpreted in terms of mixing of the a 1Δ state with the c 1Π state.

ChemInform Abstract: FAR‐INFRARED LASER MAGNETIC RESONANCE DETECTION AND MICROWAVE SPECTROSCOPY OF THE PHOSPHORUS OXIDE (PO2) RADICAL

Chemischer InformationsdienstVolume 16, Issue 36 Physical Inorganic Chemistry ChemInform Abstract: FAR-INFRARED LASER MAGNETIC RESONANCE DETECTION AND MICROWAVE SPECTROSCOPY OF THE PHOSPHORUS OXIDE (PO2) RADICAL K. KAWAGUCHI, K. KAWAGUCHISearch for more papers by this authorS. SAITO, S. SAITOSearch for more papers by this authorE. HIROTA, E. HIROTASearch for more papers by this authorN. OHASHI, N. OHASHISearch for more papers by this author K. KAWAGUCHI, K. KAWAGUCHISearch for more papers by this authorS. SAITO, S. SAITOSearch for more papers by this authorE. HIROTA, E. HIROTASearch for more papers by this authorN. OHASHI, N. OHASHISearch for more papers by this author First published: September 10, 1985 https://doi.org/10.1002/chin.198536008AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume16, Issue36September 10, 1985 RelatedInformation

Far-infrared laser magnetic resonance detection and microwave spectroscopy of the PO2 radical

Pure rotational transitions of the PO2 radical have been detected for the first time by far-infrared laser magnetic resonance with a CO2 laser pumped laser as a source. The radical was generated by the reaction of red phosphorus with mirowave discharge products of an H2/O2 mixture. Microwave spectroscopy was subsequently applied to a similar reaction system to observe rotational transitions in the region of 82–161 GHz. The microwave and far-infrared spectra thus observed were simultaneously analyzed using an asymmetric-rotor Hamiltonian which includes the spin-rotation and hyperfine interactions, to determine the rotational, spin rotation interaction, and magnetic hyperfine interaction constants. The observed rotational constants yield the r0 structure: r0 (P–O)=1.4665(41) Å and θ0(OPO)=135°17′(50), and the centrifugal distortion constants obtained give estimates for the vibrational frequencies: ω1=1090 cm−1, ω2=377 cm−1, and ω3=1278 cm−1.