Browsing by Author "Lee, YP"

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Detection of vibration-rotational band 5-0 of (CO)-C-12-O-16 X (1)Sigma(+) with cavity ringdown absorption near 0.96 mu m
(2005-09-08)
Chung, CY
;
Ogilvie, JF
;
Lee, YP
;
應用化學系
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應用化學系分子科學碩博班
We have recorded extremely weak absorption in the overtone band 5-0 of (CO)-C-12-O-16 X (1)Sigma(+) near 0.96 mu m with cavity ringdown spectroscopy; the light source was a Raman-shifted dye laser pumped with a frequency doubled Nd:YAG laser. This band shows lines in branch P to be much more intense than corresponding lines in branch R, in contrast to all lower overtone bands v-0 (v = 1-4). This reversal in relative intensity is explained quantitatively in terms of a radial function for the electric dipolar moment of CO. We have estimated absorption line strengths for P-3-P-18 in band 5-0 of (CO)-C-12-O-16; these strengths are consistent with a pure vibrational matrix element (5 vertical bar p(x)vertical bar 0) = (3.6 +/- 0.3) x 10(-36) C m of the electric dipolar moment p(x), a Herman-Wallis coefficient C-0(5) of about -0.1, and a band strength of (5.1 +/- 1.3) x 10(-29) m at 293 K.
Divide-and-conquer learning and modular perceptron networks
(2001-03-01)
Fu, HC
;
Lee, YP
;
Chiang, CC
;
Pao, HT
;
資訊工程學系
A novel modular perceptron network (MPN) and divide-and-conquer learning (DCL) schemes for the design of modular neural networks are proposed, When a training process in a multilayer perceptron fails into a local minimum or stalls in a flat region, the proposed DCL scheme is applied to divide the current training data region (e.g,, a hard to be learned training set) into two easier (hopely) to be learned regions. The learning process continues when a self-growing perceptron network and its initial weight estimation are constructed for one of the newly partitioned regions, Another partitioned region will resume the training process on the original perceptron network. Data region partitioning, weight estimating and learning are iteratively repeated until all the training data are completely learned by the MPN We have evaluated and compared the proposed MPN with several representative neural networks on the two-spirals problem and real-world dataset, The MPN achieves better weight learning performance by requiring much less data presentations (99.01% similar to 87.86% lesser) during the network training phases, and better generalization performance (4.0% better), and less processing time (2.0% similar to 81.3% lesser) during the retrieving phase, On learning the real-world data, the MPN's show less overfitting compared to single MLP. In addition, due to its self-growing and fast local learning characteristics, the modular network (MPN) can easily adapt to on-line and/or incremental Learning requirements for a rapid changing environment.
Experimental and quantum-chemical studies on photoionization and dissociative photoionization of CH2Br2
(2004-02-15)
Chiang, SY
;
Fang, YS
;
Sankaran, K
;
Lee, YP
;
應用化學系
The dissociative photoionization of CH2Br2 in a region similar to10-24 eV was investigated with photoionization mass spectroscopy using a synchrotron radiation source. An adiabatic ionization energy of 10.25 eV determined for CH2Br2 agrees satisfactorily with predictions of 10.26 and 10.25 eV with G2 and G3 methods, respectively. Observed major fragment ions CH2Br+, CHBr+, and CBr+ show appearance energies at 11.22, 12.59, and 15.42 eV, respectively; minor fragment ions CHBr2+, Br+, and CH2+ appear at 12.64, 15.31, and 16.80 eV, respectively. Energies for formation of observed fragment ions and their neutral counterparts upon ionization of CH2Br2 are computed with G2 and G3 methods. Dissociative photoionization channels associated with six observed fragment ions are proposed based on comparison of determined appearance energies and predicted energies. An upper limit of DeltaH(f,298)(0)(CHBr+)less than or equal to300.7+/-1.5 kcal mol(-1) is derived experimentally; the adiabatic ionization energy of CHBr is thus derived to be less than or equal to9.17+/-0.23 eV. Literature values for DeltaH(f,298)(0)(CBr+)=362.5 kcal mol(-1) and ionization energy of 10.43 eV for CBr are revised to be less than 332 kcal mol(-1) and 9.11 eV, respectively. Also based on a new experimental ionization energy, DeltaH(f,298)(0)(CH2Br2+) is revised to be 236.4+/-1.5 kcal mol(-1). (C) 2004 American Institute of Physics.
Experimental and theoretical investigations of rate coefficients of the reaction S(P-3)+O-2 in the temperature range 298-878 K
(2004-11-01)
Lu, CW
;
Wu, YJ
;
Lee, YP
;
Zhu, RS
;
Lin, MC
Rate coefficients of the reaction S+O-2 with Ar under 50 Torr in the temperature range 298-878 K were determined with the laser photolysis technique. S atoms were generated by photolysis of OCS with a KrF excimer laser at 248 nm; their concentration was monitored via resonance fluorescence excited by atomic emission of S produced from microwave-discharged SO2. Our measurements show that k(298 K)=(1.92+/-0.29)x10(-12) cm(3) molecule(-1) s(-1), in satisfactory agreement with previous reports. New data determined for 505-878 K show non-Arrhenius behavior; combining our results with data reported at high temperatures, we derive an expression k(T)=(9.02+/-0.27)x10(-19)T(2.11+/-0.15) exp[(730+/-120)/T] cm(3) molecule(-1) s(-1) for 298less than or equal toTless than or equal to3460 K. Theoretical calculations at the G2M (RCC2) level, using geometries optimized with the B3LYP/6-311+G(3df) method, yield energies of transition states and products relative to those of the reactants. Rate coefficients predicted with multichannel RRKM calculations agree satisfactorily with experimental observations; the reaction channel via SOO((1)A') dominates at T<500 K, whereas channels involving formation of SOO((3)A") followed by isomerization to SO2 before dissociation, and formation of SOO((1)A") followed by direct dissociation, become important at high temperatures, accounting for the observed rapid increase in rate coefficient. (C) 2004 American Institute of Physics.
Experimental and theoretical studies of rate coefficients for the reaction O(P-3)+CH3OH at high temperatures
(2005-06-22)
Lu, CW
;
Chou, SL
;
Lee, YP
;
Xu, SC
;
Xu, ZF
Rate coefficients of the reaction O(P-3)+CH3OH in the temperature range of 835-1777 K were determined using a diaphragmless shock tube. O atoms were generated by photolysis of SO2 with a KrF excimer laser at 248 nm or an ArF excimer laser at 193 nm; their concentrations were monitored via atomic resonance absorption excited by emission from a microwave-discharged mixture of O-2 and He. The rate coefficients determined for the temperature range can be represented by the Arrhenius equation, k(T)=(2.29 +/- 0.18)x10(-10) exp[-(4210 +/- 100)/T] cm(3) molecule(-1) s(-1); unless otherwise noted, all the listed errors represent one standard deviation in fitting. Combination of these and previous data at lower temperature shows a non-Arrhenius behavior described as the three-parameter equation, k(T)=(2.74 +/- 0.07)x10(-18)T(2.25 +/- 0.13) exp[-(1500 +/- 90)/T] cm(3)molecule(-1) s(-1). Theoretical calculations at the Becke-3-Lee-Yang-Parr (B3LYP)/6-311+G(3df,2p) level locate three transition states. Based on the energies computed with coupled clusters singles, doubles (triples) [CCSD(T)]/6-311+G(3df,2p)//B3LYP/6-311+G(3df,2p), the rate coefficients predicted with canonical variational transition state theory with small curvature tunneling corrections agree satisfactorily with the experimental observations. The branching ratios of two accessible reaction channels forming OH+CH2OH (1a) and OH+CH3O (1b) are predicted to vary strongly with temperature. At 300 K, reaction (1a) dominates, whereas reaction (1b) becomes more important than reaction (1a) above 1700 K. (c) 2005 American Institute of Physics.
Experimental and theoretical studies of the rate coefficients of the reaction O(P-3)+HCl at high temperatures
(2002-10-31)
Hsiao, CC
;
Lee, YP
;
Wang, NS
;
Wang, JH
;
Lin, MC
Rate coefficients of the reaction O(P-3) + HCl in the temperature range 1093-3197 K were determined using a diaphragmless shock tube. O atoms in the ground electronic P-3 states were generated either by photolysis Of SO2 with a KrF excimer laser at 248 nm or by pyrolysis of N2O with the shock wave. Their concentrations were monitored via atomic resonance absorption excited by emission from a microwave-discharged mixture of O-2 and He. Rate coefficients determined in this work show non-Arrhenius behavior, with values consistent with previously reported. measurements for T < 1486 K; they fit well with the equation k(1)(T) = (9.27 +/- 0.03) X 10(-24) T3.67+/-0.18 exp[-(1030 +/- 160)/T] cm(3) molecule(-1) s(-1); listed errors represent one standard deviation in fitting. Theoretical calculations at the CCSD(T)/6-311 +G(d, p) level locate a bent (3)A" (TS1) and a linear (3)A' (TS3) transition state characterized previously. On the basis of the results computed by CCSD(T)/ 6-311 +G(3df,2p)//CCSD(T)/6-311 +G(d,p), the rate coefficients predicted with conventional transition-state theory, including Eckart-tunneling corrections and with variational transition-state theory including zero- and small-curvature tunneling corrections, all agree satisfactorily with experimental observations.
Infrared absorption of CH3SO2 detected with time-resolved Fourier-transform spectroscopy
(2006-06-28)
Chu, LK
;
Lee, YP
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應用化學系
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應用化學系分子科學碩博班
;
Department of Applied Chemistry
A step-scan Fourier-transform spectrometer coupled with a 6.4 m multipass absorption cell was employed to detect time-resolved infrared absorption spectra of the reaction intermediate CH3SO2 radical, produced upon irradiation of a flowing gaseous mixture of CH3I and SO2 in CO2 at 248 nm. Two transient bands with origins at 1280 and 1076 cm(-1) were observed and are assigned to the SO2-antisymmetric and SO2-symmetric stretching modes of CH3SO2, respectively. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ and B3P86/aug-cc-pVTZ) predicted the geometry, vibrational, and rotational parameters of CH3SO2 and CH3OSO. Based on predicted rotational parameters, the simulated absorption band of the SO2-antisymmetric stretching mode that is dominated by the b-type rotational structure agrees satisfactorily with experimental results. In addition, a band near 1159 cm(-1) observed at a later period is tentatively attributed to CH3SO2I. The reaction kinetics of CH3+SO2 -> CH3SO2 and CH3SO2+I -> CH3SO2I based on the rise and decay of absorption bands of CH3SO2 and CH3SO2I agree satisfactorily with previous reports. (c) 2006 American Institute of Physics.
Intensities of line features in vibration-rotational bands 2-0 to 6-0 of (NO)-N-14-O-16 X-2 Pi(r) and experimental evaluation of a radial function for electric dipolar moment
(2006-01-01)
Lee, YP
;
Cheah, SL
;
Ogilvie, JF
;
應用化學系
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應用化學系分子科學碩博班
We measured the strengths of individual line-like features, representing unresolved A doublets, in vibration-rotational bands 2-0 to 6-0 of (NO)-N-14-O-16 within each substate of electronic ground state X(2)Pi(1/2,3/2) in mid and near infrared regions. Analyses of these data to derive values of matrix element; for vibrational transitions enabled production of a radial function for electric dipolar moment, containing seven parameters, that satisfactorily reproduces the intensities of about 700 such features for vibrational states up to v = 6. (c) 2005 Elsevier B.V. All rights reserved.
Internal rotation and spin conversion of CH3OH in solid para-hydrogen
(2006-01-20)
Lee, YP
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Wu, YO
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Lees, RM
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Xu, LH
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Hougen, JT
The quantum solid para-hydrogen (p-H-2) has recently proven useful in matrix isolation spectroscopy. Spectral lines of compounds embedded in this host are unusually narrow, and several species have been reported to rotate in p-H-2. We found that a p-H-2 matrix inhibits rotation of isolated methanol (CH3OH) but still allows internal rotation about the C-O bond, with splittings of the E/A torsional doublet in internal rotation-coupled vibrational modes that are qualitatively consistent with those for CH3OH in the gaseous phase. This simplified high-resolution spectrum further revealed the slow conversion of nuclear spin symmetry from species E to species A in the host matrix, offering potential insight into nuclear spin conversion in astrophysical sources.
Isomers of GeNO and Ge(NO)(2): Production and infrared absorption of GeNO and ONGeNO in solid Ar
(2005-08-01)
Chou, JB
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Bahou, M
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Lee, YP
;
Rayner, D
;
Simard, B
Crystalline germanium was ablated with light at 532 nm from a frequency-doubled neodymium: yttrium aluminum garnet laser, and the resultant plume reacted with NO before deposition onto a substrate at 13 K. Lines in group A at 1543.8 and 3059.7 cm(-1) that become enhanced at the initial stage of irradiation at 308 or 193 nm and also after annealing are attributed to nu(1) and 2 nu(1) of GeNO. Lines in group B at 1645.5 and 1482.8 cm(-1) that become diminished after further irradiation of the matrix at 308 or 193 nm but become enhanced after annealing are attributed to symmetric NO stretch (nu(1)) and antisymmetric NO stretch (nu(7)) of ONGeNO. The assignments were derived based on wave numbers and isotopic ratios observed in the experiments with N-15- and O-18-isotopic substitutions and predicted with quantum-chemical calculations. Quantum-chemical calculations with density-functional theories (B3LYP and BLYP/aug-cc-pVTZ) predict four stable isomers of GeNO, six isomers of Ge2NO, and four isomers of Ge(NO)(2), with linear GeNO, cyc-GeNGeO, and cyc-GeONNO having the least energies, respectively. The formation mechanisms of GeNO and ONGeNO are discussed. In addition, a weak line at 1417.0 cm(-1) and two additional lines associated with minor matrix sites at 1423.0 and 1420.3 cm(-1) are assigned to GeNO-. (C) 2005 American Institute of Physics.
Isomers of NCO2: IR-absorption spectra of ONCO in solid Ne
(2005-11-01)
Wu, YJ
;
Lee, YP
;
應用化學系
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應用化學系分子科學碩博班
;
Department of Applied Chemistry
Irradiation of a Ne matrix sample containing NO and CO near 4 K with an ArF excimer laser at 193 nm yielded new lines at 2045.1 and 968.0 cm(-1) that were depleted upon secondary photolysis at 308 nm. These lines are assigned to C=O stretching and mixed stretching modes of ONCO, based on results of N-15-, C-13-, and O-18-isotopic experiments and quantum-chemical calculations. These calculations using density-functional theory (B3LYP and PW91PW91/aug-cc-pVTZ) predict five stable isomers of NCO2: ONCO, NCOO, N-cyc-CO2, CNOO, and cyc-CNOO, listed in order of increasing energy. According to B3LYP calculations, ONCO has a trans configuration, with bond angles of angle ONC congruent to 136.3 degrees and angle NOC congruent to 160.7 degrees. Calculated vibrational wave numbers, IR intensities, N-15-, C-13-, and O-18-isotopic shifts for ONCO agree satisfactorily with experimental results. ONCO was formed from reaction of CO with NO in its excited state. (c) 2005 American Institute of Physics.Irradiation of a Ne matrix sample containing NO and CO near 4 K with an ArF excimer laser at 193 nm yielded new lines at 2045.1 and 968.0 cm(-1) that were depleted upon secondary photolysis at 308 nm. These lines are assigned to C = O stretching and mixed stretching modes of ONCO, based on results of N-15-, C-13-, and O-18-isotopic experiments and quantum-chemical calculations. These calculations using density-functional theory (B3LYP and PW91PW91/aug-cc-pVTZ) predict five stable isomers of NCO2: ONCO, NCOO, N-cyc-CO2, CNOO, and cyc-CNOO, listed in order of increasing energy. According to B3LYP calculations, ONCO has a trans configuration, with bond angles of > ONC congruent to 136.3 degrees and > NOC congruent to 160.7 degrees. Calculated vibrational wave numbers, IR intensities, N-15-, C-13-, and O-18-isotopic shifts for ONCO agree satisfactorily with experimental results. ONCO was formed from reaction of CO with NO in its excited state.
Isomers of OCS2: IR absorption spectra of OSCS and O(CS2) in solid ar
(2004-12-22)
Lo, WJ
;
Chen, HF
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Chou, PH
;
Lee, YP
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應用化學系
Irradiation of an Ar matrix sample containing O-3 and CS2 with a KrF excimer laser at 248 nm yielded new lines at 1402.1 (1404.7), 1056.2 (1052.7), and 622.3 (620.5) cm-1; numbers in parentheses correspond to species in a minor matrix site. Secondary photolysis at 308 nm diminished these lines and produced mainly OCS and SO2. Annealing of this matrix to 30 K yielded a second set of new lines at 1824.7 and 617.8 cm-1. The first set of lines are assigned to C=S stretching, O-S stretching, and S-C stretching modes of carbon disulfide S-oxide, OSCS; and the second set of lines are assigned to C=O stretching and OCS bending modes of dithiiranone, O(CS2), respectively, based on results of S-34- and O-18-isotopic experiments and quantum-chemical calculations. These calculations using density-functional theory (B3LYP/aug-cc-pVTZ) predict four stable isomers of OCS2: O(CS2), SSCO, OSCS, and SOCS, listed in order of increasing energy. According to calculations, O(CS2) has a cyclic CS2 moiety and is the most stable isomer of OCS2. OSCS is planar, with bond angles angleOSCcongruent to111.9degrees and angleSCScongruent to177.3degrees; it is less stable than SSCO and O(CS2) by similar to102 and 154 kJ mol-1, respectively, and more stable than SOCS by similar to26 kJ mol-1. Calculated vibrational wave numbers, IR intensities, S-34- and O-18-isotopic shifts for OSCS and O(CS2) fit satisfactorily with experimental results. (C) 2004 American Institute of Physics.
Kinetics of the CH3S+O-3 reaction.
(1997-09-07)
Wang, NS
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Chew, EP
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Lin, JT
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Lee, YY
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Lee, YP
Kinetics of the CH3S+O-3 reaction.
(1997-09-07)
Wang, NS
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Chew, EP
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Lin, JT
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Lee, YY
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Lee, YP
Molecular elimination in photolysis of fluorobenzene at 193 nm: Internal energy of HF determined with time-resolved Fourier-transform spectroscopy
(2004-11-08)
Wu, CY
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Wu, YJ
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Lee, YP
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應用化學系
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Department of Applied Chemistry
Following photodissociation of fluorobenzene (C6H5F) at 193 nm, rotationally resolved emission spectra of HF(1less than or equal toupsilonless than or equal to4) in the spectral region 2800-4000 cm-1 are detected with a step-scan Fourier-transform spectrometer. In the period 0.1-1.1 mus after photolysis, HF(upsilonless than or equal to4) shows similar Boltzmann-type rotational distributions corresponding to a temperature similar to1830 K; a short extrapolation from data in the period 0.1-4.1 mus leads to a nascent rotational temperature of 1920+/-140 K with an average rotational energy of 15+/-3 kJ mol(-1). The observed vibrational distribution of (upsilon = 1):(upsilon = 2):(upsilon = 3):(upsilon = 4)=(60+/-7):(24+/-3):(10.5+/-1.2):(5.3+/-0.5) corresponds to a vibrational temperature of 6400+/-180 K. An average vibrational energy of 33+/-9/3 kJ mol(-1) is derived based on the observed population of HF(1less than or equal toupsilonless than or equal to4) and an estimate of the population of HF(upsilon=0) by extrapolation. The observed internal energy distribution of HF is consistent with that expected for the four-center (alpha,beta) elimination channel. A modified impulse model taking into account geometries and displacement vectors of transition states during bond breaking predicts satisfactorily the rotational excitation of HF. We also compare internal energies of HF observed in this work with those from photolysis of vinyl fluoride (CH2CHF) and 2-chloro-1,1-difluoroethene (CF2CHCl) at 193 nm. (C) 2004 American Institute of Physics.
Molecular elimination in photolysis of o- and p-fluorotoluene at 193 nm: Internal energy of HF determined with time-resolved Fourier transform spectroscopy
(2005-12-08)
Yang, SK
;
Liu, SY
;
Chen, HF
;
Lee, YP
;
應用化學系
Following the photodissociation of o-fluorotoluene [o-C6H4(CH3)F] at 193 nm, rotationally resolved emission spectra of HF(1 <= v <= 4) in the spectral region of 2800-4000 cm(-1) are detected with a step-scan Fourier transform spectrometer. HF(v <= 4) shows nearly Boltzmann-type rotational distributions corresponding to a temperature similar to 1080 K; a short extrapolation from data in the period of 0.5-4.5 mu s leads to a nascent rotational temperature of 1130 +/- 100 K with an average rotational energy of 9 +/- 2 kJ mol(-1). The observed vibrational distribution of (v=1):(v=2):(v=3)=67.6: 23.2: 9.2 corresponds to a vibrational temperature of 5330 +/- 270 K. An average vibrational energy of 25 +/-(12)(3) kJ mol(-1) is derived based on the observed population of HF(1 <= v <= 3) and estimates of the population of HF (v=0 and 4) by extrapolation. Experiments performed on p-fluorotoluene [p-C6H4(CH3)F] yielded similar results with an average rotational energy of 9 +/- 2 kJ mol(-1) and vibrational energy of 26 +/-(12)(3) kJ mol(-1) for HF. The observed distributions of internal energy of HF in both cases are consistent with that expected for four-center elimination. A modified impulse model taking into account geometries and displacement vectors of transition states during bond breaking predicts satisfactorily the rotational excitation of HF. An observed vibrational energy of HF produced from fluorotoluene slightly smaller than that from fluorobenzene might indicate the involvement of seven-membered-ring isomers upon photolysis. (c) American Institute of Physics.
Photodissociation dynamics of formyl fluoride (HFCO) at 193 nm: Branching ratios and distributions of kinetic energy
(2005-08-15)
Lee, SH
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Wu, CY
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Yang, SK
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Lee, YP
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應用化學系
Following photodissociation of formyl fluoride (HFCO) at 193 nm, we detected products with fragmentation translational spectroscopy utilizing a tunable vacuum ultraviolet beam from a synchrotron for ionization. Among three primary dissociation channels observed in this work, the F-elimination channel HFCO -> HCO+F dominates, with a branching ratio similar to 0.66 and an average release of kinetic energy similar to 55 kJ mol(-1); about 17% of HCO further decomposes to H+CO. The H-elimination channel HFCO -> FCO+H has a branching ratio similar to 0.28 and an average release of kinetic energy similar to 99 kJ mol(-1); about 21% of FCO further decomposes to F+CO. The F-elimination channel likely proceeds via the S-1 surface whereas the H-elimination channel proceeds via the T-1 surface; both channels exhibit moderate barriers for dissociation. The molecular HF-elimination channel HFCO -> HF+CO, correlating with the ground electronic surface, has a branching ratio of only similar to 0.06; the average translational release of 93 kJ mol(-1), similar to 15% of available energy, implies that the fragments are highly internally excited. Detailed mechanisms of photodissociation are discussed. (c) 2005 American Institute of Physics.
Photodissociation dynamics of vinyl chloride investigated with a pulsed slit-jet and time-resolved Fourier-transform spectroscopy
(2004)
Bahou, M
;
Lee, YP
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應用化學系
;
Department of Applied Chemistry
Following photodissociation of vinyl chloride seeded in a He supersonic jet at 193 nm, rotationally resolved infrared emission of HCl ( v) are recorded to yield nascent rotational and vibrational distributions. Preliminary results show that the rotational distribution of HCl free from rotational quenching deviates slightly from Boltzmann-type distribution and agrees well with trajectory calculations; a portion of the low-J component observed previously in a flow system is attributed to quenching. The implications for photodissociation dynamics are discussed.
Photoionization spectra and ionization thresholds of CH3SO, CH3SOH, and CH3SS(O)CH3
(1996-11-01)
Hung, WC
;
Shen, MY
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Lee, YP
;
Wang, NS
;
Cheng, BM
Photoionization efficiency (PIE) spectra of CH3SO, CH3SOH, and CH3SS(O)CH3 were measured in the spectral range 110-150 nm by means of a discharge flow system coupled to a photoionization mass spectrometer that employs a synchrotron radiation source, These species were generated bq reacting O atoms with CH3SSCH3 in the flow tube; a microwave discharge was employed to produce O atoms from O-2, Alternatively, C2H5SCH3 replaced CH3SSCH3 to form CH3SO, CH3SOH, and other products. Ionization thresholds of 8.99+/-0.02, 8.67+/-0.03, and 8.82+/-0.05 eV were determined for the first time for CH3SO, CH3SOH, and CH3SS(O)CH3, respectively, The former two values agree well with theoretical calculations with the G2 method, The latter value fits satisfactorily with those predicted for CH3SS(O)CH3 with the G2MP2 method; the G2 method was not employed in this case due to the numerous atoms in this molecule. Ionization thresholds of CH3S and CH3S2 were also determined to be 9.27+/-0.03 and 8.62+/-0.05 eV, respectively. experimental reports. (C) 1996 American Institute of Physics.
Photolysis of oxalyl chloride (ClCO)(2) at 193 nm: Emission of CO(v <= 6, J <= 60) detected with time-resolved Fourier-transform spectroscopy
(2004-04-15)
Wu, CY
;
Lee, YP
;
Wang, NS
;
應用化學系
;
Department of Applied Chemistry
Upon photolysis of oxalyl chloride at 193 nm, time-resolved and rotationally resolved emission of CO(vless than or equal to6, Jless than or equal to60) in the spectral region 1850-2350 cm(-1) was detected with a step-scan Fourier-transform spectrometer under nearly collisionless conditions. Boltzmann-type rotational distributions of CO correspond to temperatures 3520+/-110 (v=1) to 2300+/-610 K (v=6), with an average rotational energy of 23+/-2 kJ mol(-1). The average vibrational energy of CO is estimated to be 26+/-4 kJ mol(-1) according to observed vibrational populations of v=1-6 and that of v=0 predicted with a surprisal analysis. Combining the average internal energy of CO determined in this work and average translational energies of photofragments Cl and CO determined previously by Hemmi and Suits, we propose a four-body dissociation mechanism producing one pair of translationally rapid and internally excited CO and one pair of translationally rapid Cl, each with similar energies, to account for the energy balance. Formation of translationally slow ClCO, Cl, and CO reported previously by Hemmi and Suits might be rationalized with a second channel involving emission of electronically excited intermediates. We observed no emission of ClCO near 1880 cm(-1), indicating that surviving ClCO has little vibrational excitation in the C-O stretching mode. (C) 2004 American Institute of Physics.