Browsing by Author "Matsui, Hiroyuki"

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A comparative study on the production yield of H atom in the thermal decomposition of i-C4H10 and n-C4H10: Examination of the contribution of the roaming radical channels
(2018-01-01)
Chen, Wei-Yu
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Matsui, Hiroyuki
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Wang, Niann-Shiah
;
應用化學系
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Department of Applied Chemistry
The yields of H atoms in the thermal decomposition of i-C4H10 -> products (1) and n-C4H10 -> products (2) are measured at 1470-1800 K behind reflected shock waves. A comparative method is used to evaluate the branching fractions for i-C4H10 -> CH3 + i-C3H7 (1a) and n-C4H10 -> 2C(2)H(5) (2b), where, C3H6 is used as a reference. The branching fractions for (1a) and (2b) are expressed by k(1a)/ k(1) = (0.64 +/- 0.14) (10 T-3/ K) - (0.06 +/- 0.23) and, k(2b)/ k(2) = (0.050 +/- 0.059)(10 T-3/ K) + (0.49 +/- 0.10), respectively. Contributions of the roaming channels are less than 12 and 5% for i-C4H10 -> CH4 + C3H6 (1b) and n-C4H10 -> CH4 + C3H6 (2c), respectively. (C) 2017 Elsevier B. V. All rights reserved.
Detailed mechanism of the CH2I + O-2 reaction: Yield and self-reaction of the simplest Criegee intermediate CH2OO
(2014-09-14)
Ting, Wei-Lun
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Chang, Chun-Hung
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Lee, Yu-Fang
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Matsui, Hiroyuki
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Lee, Yuan-Pern
The application of a new reaction scheme using CH2I + O-2 to generate the simplest Criegee intermediate, CH2OO, has stimulated lively research; the Criegee intermediates are extremely important in atmospheric chemistry. The detailed mechanism of CH2I + O-2 is hence important in understanding kinetics involving CH2OO. We employed ultraviolet absorption to probe simultaneously CH2I2, CH2OO, CH2I, and IO in the reaction system of CH2I + O-2 upon photolysis at 248 nm of a flowing mixture of CH2I2, O-2, and N-2 (or SF6) in the pressure range 7.6-779 Torr to investigate the reaction kinetics. With a detailed mechanism to model the observed temporal profiles of CH2I, CH2OO, and IO, we found that various channels of the reaction CH2I + O-2 and CH2OO + I play important roles; an additional decomposition channel of CH2I + O-2 to form products other than CH2OO or ICH2OO becomes important at pressure less than 60 Torr. The pressure dependence of the derived rate coefficients of various channels of reactions of CH2I + O-2 and CH2OO + I has been determined. We derived a rate coefficient also for the self-reaction of CH2OO as k = (8 +/- 4) x 10(-11) cm(3) molecule(-1) s(-1) at 295 K. The yield of CH2OO from CH2I + O-2 was found to have a pressure dependence on N-2 and O-2 smaller than in previous reports; for air under 1 atm, the yield of similar to 30% is about twice of previous estimates. (C) 2014 AIP Publishing LLC.
Direct measurement of site-specific rates of reactions of H with C3H8, i-C4H10, and n-C4H10
(2017-08-14)
Lin, Chia-Chieh
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Chen, Wei-Yu
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Matsui, Hiroyuki
;
Wang, Niann-Shiah
;
應用化學系
We measured the rates of abstraction of a hydrogen atom from specific sites in propane C3H8, 2-methyl propane (i-C4H10), and butane (n-C4H10); the sites are a primary hydrogen of C3H8 and i-C4H10 and a secondary hydrogen of n-C4H10. The excellent reproducibility of conditions of a diaphragm-less shock tube enabled us to conduct comparative measurements of the evolution of H atoms in three mixtures-(i) 0.5 ppm C2H5I + Ar, (ii) 0.5 ppm C2H5I + 50-100 ppm alkane as C3H8 or i-C4H10 or n-C4H10 + Ar, and (iii) the same concentrations of alkane + Ar without C2H5I-in the temperature range 1000-1200 K and at a pressure of 2.0 bars. The net profile of rise and decay of H atoms in the C2H5I + alkane mixture was derived on subtracting the absorbance of (iii) from that of (ii). Measurements of the mixture (iii) are important because the absorption of alkanes at 121.6 nm is not negligible. In the temperature range 1000-1100 K, the rate of decomposition of C2H5I was evaluated directly on analyzing the exponential growth of H atoms in the mixture (i). The rate of decomposition of C2H5I is summarized as ln(k/s(-1)) = (33.12 +/- 1.4) - (25.23 +/- 1.5) 10(3)/T (T = 1000-1100 K, P = 2.0 bars); the broadening factor F(T) in the Lindemann-Hinshelwood formula was evaluated in the fall-off region. The site-specific rates of H + (C-3-C-4) alkanes are summarized as follows: H + C3H8 -> H-2 + 1-C3H7, ln(k(1a)) = -(21.34 +/- 0.86) - (5.39 +/- 0.93) 10(3)/T, H + i-C4H10 -> H-2 + i-C4H9, ln(k(2a)) = -(20.50 +/- 1.36) - (6.14 +/- 0.13) 10(3)/T, H + n-C4H10 -> H-2 + 2-C4H9, ln(k(3b)) = - (21.37 +/- 1.15) - (4.83 +/- 1.26) 10(3)/T. The present experimental results are compared with published results from quantum-chemical calculations of potential-energy surfaces and transition-state theory. The present experiments are consistent with those calculations for the reaction rates for the attack at the primary site for H + C3H8 and H + i-C4H10, but for the attack at the secondary site of n-C4H10, our results are substantially smaller than the computational prediction, which might indicate a hindrance by the C-H bonds of the primary sites that serves to decrease the rate of abstraction from the secondary site of n-C4H10. The influence on the total rates of reactions H + alkane and the group additivity rule are discussed. Published by AIP Publishing.
Distribution of Vibrational States of CO(2) in the Reaction O((1)D) + CO(2) from Time-Resolved Fourier Transform Infrared Emission Spectra
(2009-04-16)
Chen, Hui-Fen
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Chiang, Hung-Chu
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Matsui, Hiroyuki
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Tsuchiya, Soji
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Lee, Yuan-Pern
A mixture Of O(3) and CO(2) was irradiated with light from a KrF laser at 248 nm; time-resolved infrared emission Of CO(2) in the region 2000-2400 cm(-1) was observed with a Fourier transform spectrometer. This emission involves one quantum in the asymmetric stretching mode (nu(3)) Of CO(2) in highly vibrationally excited states. The band contour agrees satisfactorily with a band shape calculated based on a simplified polyad model of CO(2) and a vibrational distribution estimated through a statistical partitioning of energy of similar to 13 000 cm(-1), similar to 3100 cm(-1) smaller than the available energy, into the vibrational modes Of CO(2). From this model, approximately 44% and 5% of the available energy of O((1)D) + CO(2) is converted into the vibrational and rotational energy of product CO(2), respectively, consistent with previous reports of similar to 50% for the translational energy. An extent of rotational excitation Of CO(2) much smaller than that expected from statistical calculations indicates a mechanism that causes a small torque to be given to CO(2) when an O atom leaves the complex CO(3) on the triplet exit surface of potential energy, consistent with quantum-chemical calculations.
Distribution of Vibrational States of CO2 in the Reaction O(D-1) + CO2 from Time-Resolved Fourier Transform Infrared Emission Spectra
(2009-04-16)
Chen, Hui-Fen
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Chiang, Hung-Chu
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Matsui, Hiroyuki
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Tsuchiya, Soji
;
Lee, Yuan-Pern
A mixture Of O-3 and CO2 was irradiated with light from a KrF laser at 248 nm; time-resolved infrared emission Of CO2 in the region 2000-2400 cm(-1) was observed with a Fourier transform spectrometer. This emission involves one quantum in the asymmetric stretching mode (nu(3)) Of CO2 in highly vibrationally excited states. The band contour agrees satisfactorily with a band shape calculated based on a simplified polyad model of CO2 and a vibrational distribution estimated through a statistical partitioning of energy of similar to 13 000 cm(-1), similar to 3100 cm(-1) smaller than the available energy, into the vibrational modes Of CO2. From this model, approximately 44% and 5% of the available energy of O(D-1) + CO2 is converted into the vibrational and rotational energy of product CO2, respectively, consistent with previous reports of similar to 50% for the translational energy. An extent of rotational excitation Of CO2 much smaller than that expected from statistical calculations indicates a mechanism that causes a small torque to be given to CO2 when an O atom leaves the complex CO3 on the triplet exit surface of potential energy, consistent with quantum-chemical calculations.
Experimental and Theoretical Study on the Thermal Decomposition of C3H6 (Propene)
(2015-02-26)
Hung, Wei-Chung
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Tsai, Chieh-Ying
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Matsui, Hiroyuki
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Wang, Niann-Shiah
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Miyoshi, Akira
Extremely rapid self-reaction of the simplest Criegee intermediate CH2OO and its implications in atmospheric chemistry
(2014-06-01)
Su, Yu-Te
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Lin, Hui-Yu
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Putikam, Raghunath
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Matsui, Hiroyuki
;
Lin, M. C.
Criegee intermediates, which are carbonyl oxides produced when ozone reacts with unsaturated hydrocarbons, play an important role in the formation of OH and organic acids in the atmosphere, but they have eluded direct detection until recently. Reactions that involve Criegee intermediates are not understood fully because data based on their direct observation are limited. We used transient infrared absorption spectroscopy to probe directly the decay kinetics of formaldehyde oxide (CH2OO) and found that it reacts with itself extremely rapidly. This fast self-reaction is a result of its zwitterionic character. According to our quantum-chemical calculations, a cyclic dimeric intermediate that has the terminal O atom of one CH2OO bonded to the C atom of the other CH2OO is formed with large exothermicity before further decomposition to 2H(2)CO + O-2 ((1)Delta(g)). We suggest that the inclusion of this previously overlooked rapid reaction in models may affect the interpretation of previous laboratory experiments that involve Criegee intermediates.
New experimental evidence to support roaming in the reaction Cl plus isobutene (i-C4H8)
(2017-01-12)
Chen, Li-Wei
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Hung, Ching-Ming
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Matsui, Hiroyuki
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Lee, Yuan-Pern
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應用化學系
The reaction Cl + isobutene (i-C4H8) was reported by Suits et al. to proceed via, in addition to abstraction, an addition-elimination path following a roaming excursion of Cl; a near-zero translational energy release and an isotropic angular distribution observed at a small collision energy characterized this mechanism. We employed a new experimental method to further characterize this roaming mechanism through observation of the internal distribution of HCl (v, J) and their temporal behavior upon irradiation of a mixture of Cl2C2O2 and i-C4H8 in He or Ar buffer gas. With 1-3 Torr buffer gas added to approach the condition of small collision energy, the intensities of emission of HCl (v = 1, 2) and the HCl production rates increased significantly; Ar shows a more significant effect than He because Ar quenches Cl more efficiently to reduce the collisional energy and facilitate the roaming path. According to kinetic modeling, the rate of addition-elimination (roaming) increased from k(E) approximate to 2 x 10(5) s(-1) when little buffer gas was present to similar to 1.9 x 106 s(-1) when 2-3 Torr of Ar was added, and the branching ratio for formation of [HCl (v = 2)]/[ HCl (v = 1)] increased from 0.02 +/- 0.01 for abstraction to 0.06 +/- 0.01 for roaming.
Product branching fractions for the reaction of O((3)P) with ethene
(2009-01-01)
Miyoshi, Akira
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Yoshida, Jun-ichi
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Shiki, Naoya
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Koshi, Mitsuo
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Matsui, Hiroyuki
The product branching fractions for the reaction of atomic oxygen with ethene, O((3)P) + C(2)H(4) -> CH(3) + HCO (1a), -> H + CH(2)CHO (1b), -> H(2) + CH(2)CO (1c), have been investigated at room temperature (295 +/- 4 K) and pressures from 1 to 4 Torr (with N(2) or He buffer) by a laser photolysis-photoionization mass spectrometry method. From the yield of CH(3) radical, phi(CH(3)), the branching fraction for (1a) was determined to be 0.53 +/- 0.04 and no apparent pressure dependence was found from 1.5 to 4.0 Torr (N(2) buffer). The ratio of the HCO yield to that of CH(3), phi(HCO)/phi(CH(3)), was measured to be less than unity and increased as pressure increased (similar to 0.7 at 1 Torr and similar to 0.9 at 4 Torr [ He]) suggesting prompt dissociation of the hot HCO radical (to H + CO) formed by channel (1a) at low pressures. An interpretation which reduces the large discrepancy among branching fractions reported for low pressure region is presented. The existence of the molecular H(2)-elimination channel (1c) was confirmed. The branching fraction for channel (1c) was determined to be 0.019 +/- 0.001 by the yield of CH(2)CO and was independent of pressure from 1.0 to 4.0 Torr (He buffer). As a side result, the yield of CH(3) radical from O((1)D) + C(2)H(4) reaction was also determined.
Product branching fractions for the reaction of O(P-3) with ethene
(2009)
Miyoshi, Akira
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Yoshida, Jun-ichi
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Shiki, Naoya
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Koshi, Mitsuo
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Matsui, Hiroyuki
The product branching fractions for the reaction of atomic oxygen with ethene, O(P-3) + C2H4 -> CH3 + HCO (1a), -> H + CH2CHO (1b), -> H-2 + CH2CO (1c), have been investigated at room temperature (295 +/- 4 K) and pressures from 1 to 4 Torr (with N-2 or He buffer) by a laser photolysis-photoionization mass spectrometry method. From the yield of CH3 radical, phi(CH3), the branching fraction for (1a) was determined to be 0.53 +/- 0.04 and no apparent pressure dependence was found from 1.5 to 4.0 Torr (N-2 buffer). The ratio of the HCO yield to that of CH3, phi(HCO)/phi(CH3), was measured to be less than unity and increased as pressure increased (similar to 0.7 at 1 Torr and similar to 0.9 at 4 Torr [ He]) suggesting prompt dissociation of the hot HCO radical (to H + CO) formed by channel (1a) at low pressures. An interpretation which reduces the large discrepancy among branching fractions reported for low pressure region is presented. The existence of the molecular H-2-elimination channel (1c) was confirmed. The branching fraction for channel (1c) was determined to be 0.019 +/- 0.001 by the yield of CH2CO and was independent of pressure from 1.0 to 4.0 Torr (He buffer). As a side result, the yield of CH3 radical from O(D-1) + C2H4 reaction was also determined.
Production of H and O(P-3) Atoms in the Reaction of CH2 with O-2
(2012-09-20)
Lee, Pei-Fang
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Matsui, Hiroyuki
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Chen, Wei-Yu
;
Wang, Niann-Shiah
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應用化學系
The reaction CH2 + O-2 -> 4 products has been studied by using atomic resonance absorption spectrometry (ARAS) of H and O(P-3) atoms behind reflected shock waves over 1850-2050 K and 2.1-1.7 atm. Measurements of [H] and [O] are conducted using mixtures of highly diluted CH2I2 (0.2 and 0.4 ppm) with excess O-2 (100 and 262 ppm) in Ar; comparative measurement of [H] in the 0.2 and 0.4 ppm CH2I2 + 300 ppm H-2 mixture has been conducted simultaneously to confirm the initial concentration of CH2. The apparent reaction rate of CH2 + O-2 (k(2)'), including the contributions of (CH2)-C-3 + O-2 -> products (2) and (CH2)-C-1 + O-2 -> products (3), has been measured from the evolutions of [H] and [O] and summarized as k(2)'/cm(3) molecule(-1) s(-1) = (1.90 +/- 0.31) x 10(-11). The contribution of (CH2)-C-1 + O-2 reaction on the measured k(2)' has been evaluated as 0.15 +/- 0.04, with an assumption that k(3) is independent of temperature and given by the result measured at room temperature [Langford, A. O.; Petek, H.; Moore, C. B. J. Chem. Phys. 1983, 78, 6650-6659]. The net rate for the (CH2)-C-3 + O-2 reaction is given as k(2)/cm(3) molecule(-1) s(-1) = (1.69 +/- 0.31) x 10(-11). The result on k(2) in this study is found to be consistent with the extrapolation of the previous work at lower temperature range of 295-600 K. [Vinckler, C.; Debruyn, W. J. Phys. Chem. 1979, 83, 2057-2062]; these results can be summarized as k(2)/cm(3) molecule(-1) s(-1) = 2.74 x 10(-11) exp(-874/T), (T = 295-2050 K). The apparent production yields of H and O atoms for the reaction channels (CH2)-C-1,3 + O-2 -> H + products (2a, 3a) and (1)'(CH2)-C-3 + O-2 -> O(P-3) + products (2h, 3b) have been evaluated as phi(2a)' = 0.59 +/- 0.06 and phi(2b)' = 0.23 +/- 0.06, respectively. The contributions of (CH2)-C-1 + O-2 reaction on measured phi(2a)' and phi(2b)' are indicated to be minor; the net branching fractions for the (CH2)-C-3+O-2 reaction are estimated as phi(2a) = 0.58 +/- 0.06 and phi(2b) = 0.25 +/- 0.06. No obvious temperature dependence is indicated in the measured rate constant nor in the branching fractions of H and 0 atoms. The mechanism of the reaction of CH2 with O-2 is discussed based on the result of the present study together with those of the previous theoretical/experimental studies.
Shock Tube Study on the Thermal Decomposition of CH(3)OH
(2010-05-06)
Lu, Ku-We
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Matsui, Hiroyuki
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Huang, Ching-Liang
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Raghunath, P.
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Wang, Niann-Shiah
H atom produced in the thermal decomposition of CH(3)OH highly diluted in Ar (0.48-10 ppm) was monitored behind reflected shock waves by atomic resonance absorption spectrometry (ARAS) at fixed temperatures (and pressures), that is, 1660 (1.73 atm), 1760 (2.34 atm), 1860 (2.04 atm), 1950 (2.18 atm), and 2050 K (1.76 atm) (+/- 10 K, respectively). High sensitivity for the H atom has been attained by signal averaging of the ARAS signals down to the concentrations of similar to 1 x 10(11) atoms/cm(3) and enables us to determine the branching fraction for the direct H atom production channel, CH(3)OH -> CH(2)OH + H (channel 1c) in a mixture of 1 ppm CH(3)OH. Channel 1c is confirmed to be minor, that is, branching fraction for channel 1c is expressed by Log(k(1c)/k(1)) = (- 2.88 +/- 1.88) x 10(3)/T - (0.23 +/- 1.02), which corresponds to k(1c)/k(1) < 0.03 for the present temperature range. By using 0.48 and 1.0 ppm CH(3)OH with (100-1000) ppm H(2), the total decomposition rate k(1) for CH(3)OH -> products is measured from the time dependence of H atom, where the radical products of main channels 1a and 1b, that is, OH, CH(3), and CH(2), were converted rapidly into H atoms. The experimental result is summarized as Log(k(1)/cm(3)molecule(-1)s(-1)) = (-12.82 +/- 0.71) x 10(3)/T - (8.5 +/- 0.38). A theoretical study based on ab initio/TST calculations with high accuracy has been conducted for the reaction: (3)CH(2) + H(2) -> CH(3) + H (reaction 3). The rate is given by k(3)/cm(3)molecule(-1) s(-1) = (7.32 x 10(-19))T(2.3) exp (-3699/T). This result is used for numerical simulations to evaluate k(1). Present experimental results on the thermal decomposition rate of CH(3)OH are found to be consistent with previous works. It is also found that time dependence of [H] observed in the 10 ppm CH(3)OH in Ar can be reproduced very well by kinetic simulations by using a reaction mechanism composed of 36 elementary reactions.
Shock Tube Study on the Thermal Decomposition of CH3OH
(2010-05-06)
Lu, Ku-We
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Matsui, Hiroyuki
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Huang, Ching-Liang
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Raghunath, P.
;
Wang, Niann-Shiah
H atom produced in the thermal decomposition of CH3OH highly diluted in Ar (0.48-10 ppm) was monitored behind reflected shock waves by atomic resonance absorption spectrometry (ARAS) at fixed temperatures (and pressures), that is, 1660 (1.73 atm), 1760 (2.34 atm), 1860 (2.04 atm), 1950 (2.18 atm), and 2050 K (1.76 atm) (+/- 10 K, respectively). High sensitivity for the H atom has been attained by signal averaging of the ARAS signals down to the concentrations of similar to 1 x 10(11) atoms/cm(3) and enables us to determine the branching fraction for the direct H atom production channel, CH3OH -> CH2OH + H (channel 1c) in a mixture of 1 ppm CH3OH. Channel 1c is confirmed to be minor, that is, branching fraction for channel 1c is expressed by Log(k(1c)/k(1)) = (- 2.88 +/- 1.88) x 10(3)/T - (0.23 +/- 1.02), which corresponds to k(1c)/k(1) < 0.03 for the present temperature range. By using 0.48 and 1.0 ppm CH3OH with (100-1000) ppm H-2, the total decomposition rate k(1) for CH3OH -> products is measured from the time dependence of H atom, where the radical products of main channels 1a and 1b, that is, OH, CH3, and CH2, were converted rapidly into H atoms. The experimental result is summarized as Log(k(1)/cm(3)molecule(-1)s(-1)) = (-12.82 +/- 0.71) x 10(3)/T - (8.5 +/- 0.38). A theoretical study based on ab initio/TST calculations with high accuracy has been conducted for the reaction: (CH2)-C-3 + H-2 -> CH3 + H (reaction 3). The rate is given by k(3)/cm(3)molecule(-1) s(-1) = (7.32 x 10(-19))T-2.3 exp (-3699/T). This result is used for numerical simulations to evaluate k(1). Present experimental results on the thermal decomposition rate of CH3OH are found to be consistent with previous works. It is also found that time dependence of [H] observed in the 10 ppm CH3OH in Ar can be reproduced very well by kinetic simulations by using a reaction mechanism composed of 36 elementary reactions.
Shock Tube Study on the Thermal Decomposition of Ethanol
(2011-07-21)
Wu, Chih-Wei
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Matsui, Hiroyuki
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Wang, Niann-Shiah
;
Lin, M. C.
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應用化學系
The thermal decomposition of C(2)H(5)OH highly diluted in Ar (1 and 3 ppm) has been studied by monitoring H atoms using the atomic resonance absorption spectrometry (ARAS) technique behind reflected shock waves over the temperature range 1450-1760 K at fixed pressure: 1, 1.45, and 2 atm. The rate constant and the product branching fractions have been determined by analyzing temporal profiles of H atoms; the effect of the secondary reactions on the results has been examined by using a detailed reaction mechanism composed of 103 elementary reactions. The apparent rate constant of ethanol decomposition can be expressed as k(1)/s(-1) = (5.28 +/- 0.14) x 10(10) exp[-(23 530 +/- 980)/T] (T = 1450-1670 K, P = 1-2 atm) without a detectable pressure dependence within the tested pressure range of this study. Branching fractions for producing CH(3) + CH(2)OH (1a) and H(2)O + C(2)H(4) (1b) have been examined by a quantitative measurement of H atoms produced in the successive decompositions of the products CH(2)OH (1a): the pressure dependence of the branching fraction for channel 1a is obtained by a linear least-squares analysis of the experimental data and can be expressed as phi(1a) = (0.71 +/- 0.07) - (826 +/- 116)/T, (0.92 +/- 0.04) (1108 +/- 70)/T, and (1.02 +/- 0.10) (1229 +/- 168)/T for T = 1450-1760 K, at P = 0.99, 1.45, and 2.0 atm, respectively. The rate constant obtained in this study is found to be consistent with previous theoretical and experimental results; however, the pressure dependence of the branching fraction obtained in this study is smaller than those of previous theoretical works. Modification of the parameters for the decomposition rate in the falloff region is suggested to be important to improve the practical modeling of the pyrolysis and combustion of ethanol
Study on the Reaction of CH2 with H-2 at High Temperature
(2012-03-01)
Lee, Pei-Fang
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Matsui, Hiroyuki
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Wang, Niann-Shiah
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應用化學系
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Department of Applied Chemistry
Thermal decomposition of CH2I2 [sequential C-I bond fission processes, CH2I2 + Ar -> CH2I + I + Ar (1a) and CH2I + Ar -> (CH2)-C-3 + I + Ar (1b)], and the reactions of (CH2)-C-3 + H-2 -> CH3 H (2) and (CH2)-C-1 + H-2 -> CH3 + H (3) have been studied by using atomic resonance absorption spectrometry (ARAS) of I and H atoms behind reflected shock waves. Highly diluted CH2I2 (0.1-0.4 ppm) with/without excess H-2 (300 ppm) in Ar has been used so that the effect of the secondary reactions can be minimized. From the quantitative measurement of I atoms in the 0.1 ppm CH2I2 + Ar mixture over 1550-2010 K, it is confirmed that two-step sequential C-I bond fission processes of CH2I2, (la) and (1b), dominate over other product channels. The decomposition step (1b) is confirmed to be the rate determining process to produce 3CH2 and the least-squares analysis of the measured rate gives, In(k(1b)/cm(3) molecule(-1) s(-1)) = -(17.28 +/- 0.79) - (30.17 +/- 1.40) x 10(3)/T. By utilizing this result, we examine reactions 2 and 3 by monitoring evolution of H atoms in the 0.2-0.4 ppm CH2I2 + 300 ppm H2 mixtures over 18502040 K. By using a theoretical result on k(2) (Lu, K. W.; Matsui, H.; Huang, C.-L.; Raghunath, P.; Wang, N.-S.; Lin, M. C. J. Phys. Chem. A 2010, 114, 5493), we determine the rate for (3) as k(3)/cm(3) molecule(-1) s(-1) = (1.27 +/- 0.36) x 10(-10). The upper limit of k(3) (k(3max)) is also evaluated by assuming k(2) = 0, i.e., k(3max)/cm(3) molecule(-1) s(-1) = (2.26 +/- 0.59) x 10(-10). The present experimental results on k(3) and k(3max) is found to agree very well with the previous frequency modulation spectroscopy study (Friedrichs, G.; Wagner, H. G. Z. Phys. Chem. 2001, 215, 1601); i.e., the importance of the contribution of (CH2)-C-1 in the reaction of CH2 with H-2 at elevated temperature range is reconfirmed.
Thermal Decomposition and Oxidation of CH3OH
(2013-01-24)
Lee, Pei-Fang
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Matsui, Hiroyuki
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Xu, Ding-Wei
;
Wang, Niann-Shiah
;
應用化學系
Thermal decomposition of CH3OH diluted in Ar has been studied by monitoring H atoms behind reflected shock waves of 100 ppm CH3OH + Ar. The total decomposition rate k(1) for CH3OH + M -> products obtained in this study is expressed as, ln(k(1)/cm(3) molecule(-1) s(-1)) = -(14.81 +/- 1.22) - (38.86 +/- 1.82) X 10(3)/T, over 1359-1644 K. The present result on k(1) is indicated to be substantially smaller than the extrapolation of the most of the previous experimental data but consistent with the published theoretical results [Faraday Discuss. 2002, 119, 191-205 and J. Phys. Chem. A 2007, 111, 3932-3950]. Oxidation of CH3OH has been studied also by monitoring H atoms behind shock waves of (0.35-100) ppm CH3OH + (100-400) ppm O-2 + Ar. For the low concentration CH3OH (below 10 ppm) + O-2 mixtures, the initial concentration of CH3OH is evaluated by comparing evolutions of H atoms in the same concentration of CH3OH with addition of 300 ppm H-2 diluted in Ar. The branching fraction for CH3OH + Ar -> (CH2)-C-1 + H2O + Ar has been quantitatively evaluated from this comparative measurements with using recent experimental result on the yield of H atoms in the reaction of (CH2)-C-1,3 + O-2 [J. Phys. Chem. A 2012, 116, 9245-9254]; i.e., the branching fraction for the above reaction is evaluated as, phi(1a) = 0.20 +/- 0.04 at T = 1880-2050 K, in the 1.3 and 3.5 ppm CH3OH + 100 ppm O-2 samples. An extended reaction mechanism for the pyrolysis and oxidation of CH3OH is constructed based on the results of the present study combined with the oxidation mechanism of natural gas [GRI-Mech 3.0]; evolution of H atoms can be predicted very well with this new reaction scheme over a wide concentration range for the pyrolysis (0.36-100 ppm CH3OH), and oxidation (0.36-100 ppm CH3OH + 100/400 ppm O-2) of methanol.