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Theoretical studies on O(3P)+CH2Cl reaction mechanism
Journal of Molecular Structure (Theochem) 579 (2002) 21±29
www.elsevier.com/locate/theochem
Theoretical studies on O( 3P) 1 CH2Cl reaction mechanism Zhengyu Zhou a,b,*, Li Guo a, Chengxue Li a, Hongwei Gao a b
a Department of Chemistry, Qufu Normal University, Qufu, Shandong 273165, People's Republic of China State Key Laboratory Crystal Materials Shandong University, Shandong, Jinan 250100, People's Republic of China
Received 1 July 2001; accepted 1 August 2001
Abstract The reaction of oxygen atom with chlorinated methyl radical has been studied using density functional theory (DFT) method at 6-31111G pp level. All the geometries, vibrational frequencies and energies of different stationary points are calculated by B3LYP/6-31111G pp and the results agree with the experimental values. The vibrational frequencies and modes of the reactant, intermediates, transition states and products have been calculated, the changes of these frequencies and modes analyzed and the changes in the vibrational force constants are assigned. The relationship and the change among them can con®rm the mechanism of the reaction and the process of electron transfer. Through the analysis, the major and minor reaction channels are con®rmed. A new study method of analyzing reaction mechanism is presented. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Reaction mechanism; DFT theory; Poly channels reaction; CH2Cl free radical
1. Introduction During the rupture of hydrocarbon, some radicals are often produced, which play an important role in species of the products of combustion process (especially the radicals of the rupture of methane) and have recently been paid much attention. Incineration is an effective method for the management of halogenated hydrocarbon wastes [1,2]. How to control secondary pollution during the incineration is an important subject [3] and becomes a focus for environment chemistry and kinetics chemistry. In order to control pollution effectively, it is necessary to carry out studies of the reaction mechanism. Halogenated methyl is highly reactive when halogen atoms substitute the hydrogen atoms in the * Corresponding author. Address: Department of Chemistry, Qufu Normal University, Qufu, Shandong 273165, People's Republic of China. Tel.: 186-537-445-5474; fax: 186-537-445-8276. E-mail address: [email protected] (Z. Zhou).
methyl. Oxygen atoms O( 3P) can rapidly react with halogenated methyls and the reactions are highly exothermic. The reaction of O( 3P) with CH2Cl is more important in combustion reactions of halogenated polymers. Until date, there are only few experimental and theoretical studies on this type of reactions. Until 1997, Seetula et al. [4] used a heatable tubular reactor coupled with a photoionization mass spectrometer to obtain the overall rate constants of the reaction of oxygen atoms with chlorinated methyl radicals. CHClO and CH2O were found to be the major products and were found to generate from the decomposition of an energy rich intermediate, OCH2Cl. On one hand, the results are used for reference to control of the environmental pollution; on the other hand, they are of great importance being a part of reaction mechanism. Recently, Baoshan Wang et al. studied the reaction of O( 3P) with CH2Cl and presented the following mechanism [5] O 1 CH2 Cl ! OCH2 Cl IM1 ! H 1 CHClO
0166-1280/02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S 0166-128 0(01)00708-4
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Z. Zhou et al. / Journal of Molecular Structure (Theochem) 579 (2002) 21±29
Table 1 Ê , bond angles in degree and frequency in cm 21) Geometry, vibrational frequencies of reactant (CH2Cl) (bond length in A Method
HF
BLYP
B3LYP
B3P86
UMP2
QCISD
Energy R(C±Cl) R(C±H) /CClH /HCH v 1(A 0 ) v 2(A 0 ) v 3(A 00 ) v 4(A 0 ) v 5(A 0 ) v 6(A 00 )
2498.4996 1.7213 1.0707 116.4 122.9 468.9 858.1 1078.4 1523.6 3300.2 3452.4
2499.4422 1.729 1.0839 117.4 125.2 178.3 791.0 974.8 1372.5 3092.4 3247.8
2499.4818 1.7137 1.0776 117.5 124.9 185.4 826.4 1001.5 1412.4 3168.6 3325.7
2499.9469 1.7015 1.0781 117.6 124.7 226.5 852.4 1001.8 1412.2 3180.6 3337.6
2498.8326 1.6982 1.0774 117.56 123.8 242.8 882.6 1048.2 1474.3 3238.4 3392.5
2498.4993 1.7085 1.0805 117.6 123.7 222.4 862.3 1033.5 1459.8 3194.9 3342.9
O 1 CH2 Cl ! OCH2 Cl IM1 ! Cl 1 CH2 O
2
O 1 CH2 Cl ! OCH2 Cl IM1 ! H2 1 ClCO
3
O 1 CH2 Cl ! OCH2 Cl IM1 ! CHClOH IM2 4 O 1 CH2 Cl ! OCH2 Cl IM1 ! CHClOH IM2 ! H 1 CHClO
5
O 1 CH2 Cl ! OCH2 Cl IM1 ! CHClOH IM2 ! HCl 1 HCO
6
on structures, energies and force constants are obviously superior to results of small basis sets. At ®rst, the geometries of reactants and products are optimized at various theoretical methods such as HF, UMP2, BLYP, B3LYP, B3P86, respectively. B3LYP method is found superior to the other methods through comparison of the theoretical results with the experimental ones. Then we optimize geometries of two intermediates and six transition, which are con®rmed through IRC calculation by using B3LYP/ 6-31111G pp method, at the same time, we calculate ZPE of the stationary points on the basis of the optimized structures. All calculations were performed using the gaussian 94 program package.
O 1 CH2 Cl ! OCH2 Cl IM1 ! CHClOH IM2 ! H2 1 ClCO
7
Further, they analyzed the mechanism in terms of the changes in the energies and bond length of various species. Density functional theory (DFT) studies of this reaction are carried out in this paper. This reaction on the lowest-lying double potential energy surface using DFT methods is examined and the vibrational frequencies and vibrational modes of all species for the reaction are analyzed. The reaction mechanism is explicitly illustrated in detail. 2. Computation methods DFT methods at the 6-31111G pp basis set are used throughout in this paper. The basis set was chosen on the basis of the ®ndings that the 6-31111G pp results
3. Results and discussion 3.1. Optimized geometries of reactants, intermediates, transition and products The geometry of the reactant, CH2Cl, is optimized by HF, BLYP, B3LYP, B3P86, UMP2 and QCISD theory methods, respectively. The bond lengths, bond angles, vibrational frequencies and vibrational modes are listed in Table 1. The experimental values of the reactant (CH2Cl) geometry are not available, but its geometry can be determined semi-qualitatively through analyzing its bonding possibility, comparing with related or similar species such as methane (CH4), chloromethane (CH3Cl) and dichloromethane (CH2Cl2). Methane belongs to Td point group and its C±H length is
Z. Zhou et al. / Journal of Molecular Structure (Theochem) 579 (2002) 21±29
23
Fig. 1. Attacking modes of O( 3P).
Ê and bond angles in degree). Fig. 2. B3LYP/6-31111G pp optimized geometries of the various isomers of the reaction (bond lengths in A
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Z. Zhou et al. / Journal of Molecular Structure (Theochem) 579 (2002) 21±29
Table 2 Total energies and the relative energies of various species (B3LYP/ 6-31111G pp) (total energies in Hartree and relative energies in kJ mol 21) Species
Total energies
DH
O 1 CH2Cl Cl 1 CH2O H 1 CHClO H2 1 ClCO HCl 1 HCO OH 1 CHCl IM1 IM2 TS1 TS2 TS3 TS4 TS5 TS6
2574.5490919 2574.68222 2574.669367 2574.694067 2574.705718 2574.547271 2574.695112 2574.703733 2574.660723 2574.661234 2574.596289 2574.644592 2574.656712 2574.64822
0.0 2349.529 2315.783 2380.634 2411.223 0.005 2383.377 2406.012 2293.088 2294.430 2114.465 2250.737 2282.558 2260.262
DH expt: 2358.2 2391.6 2420.9
Ê the bond angles(/HCH) 109.58 [6]. The C±H 1.09 A Ê [6] and C±Cl length is length reduces to 1.08 A Ê in chloromethane, which belongs to C3v 1.776 A point group. Table 1 shows the C±H length ranging Ê , C±Cl length 1.70±1.73 A Ê, from 1.07 to 1.084 A which are calculated by HF and DFT methods. The results aforementioned are lower than those of methane and chloromethane because of the space
effect and inducing-effect of chlorine atom, which agrees with the experimental rules and elucidates the rationality of theoretical calculations. It can also be found in Table 1 that the predicted vibrational frequencies of HF are in worst agreement with the calculated results. There is a large overestimation of the frequencies at HF level, even the scale factors (0.89) considered the results are still worse than DFT methods, which may be due to the slightly too short bond lengths resulting from neglecting electron correlation in the theory. The results of various DFT methods are a little identical and agree well with experimental values, especially, the B3LYP is superior to other methods for predicting molecular properties and vibration frequencies. QCISD, which includes the con®guration interaction, is theoretically more accurate but it needs more time to predict. The conclusion has been recently reported in our papers [7,8]. According to aforesaid, the B3LYP/631111G pp method is chosen for optimizing geometries and predicting vibrational frequencies of all species in the reaction. According to our assumption, oxygen atom, O( 3P), has ®ve modes of attacking at the reactant, CH2Cl. It can approach CH2Cl from different atoms, like C, H and Cl atom, and from different directions. Fig. 1 shows all the modes. Except mode (3), which cannot
Fig. 3. Overall pro®le of potential energy surface for the reaction of O( 3P) with CH2Cl calculated at B3LYP level of theory.
A 0 , 786, n (C±Cl)
A 0 , 1233, d (C±H)
?A, 214, p (O±H) ?A, 271, p (C±H) ?A, 452, r (C±H) A 0 , 720, n (C±Cl) A 0 , 582, n (C±Cl) B2, 1260, r r(CH2)
?A, i1259.6, n (O±H) A 0 , i436.4, d (O±H) ?A, 367, r (O±H) A 0 , 448, d (O±C±Cl) A 0 , 335, d Cl±C±O) B1, 1202, r W(CH2)
TS5 TS6 IM2 COClH COCl COHH
CClO
A 0 , 826, n (C±Cl) A 0 , 650, r W(CH2) ?A, 379, p (C±H) A 0 , 256, d (C±O) A 0 , 480, d (C±O) ?A, 406, d (O±C±Cl)
A 0 , 185, r w(CH2) A 0 , 384, d (C±O) ?A, i859.8, n (C±H) A 0 , i1309.2, n (C±Cl) A 0 , i809.4, r W(CH2) ?A, i2020.8, d (C±H)
Sym. Freq. Assig. IM1 TS1 TS2 TS3 TS4
Reactant
Species
A 0 , 2897, n (C±H)
?A, 457, d (Cl±C±0) ?A, 310, Ringvib ?A, 669, n (C±Cl) A 00 , 948, p (C±H) A 0 , 1955, n (C±O) A1, 1531, d (CH2)
A 00 , 1002, r t(CH2) A 0 , 654, n (C±Cl) ?A, 434, p (C±H) A 0 , 871, r W(CH2) A 00 , 514, r t(CH2) ?A, 598, d (C±H) ?A, 739, n (C±Cl) A 00 , 1130, p (O±H) ?A, 1164, Framevi A 0 , 1855, n (C±O) A1, 2885, n s(CH2)
A1, 1815, n (C±O)
A 0 , 3181, n S(CH2) A 0 , 1139, n (C±O) ?A, 685, n (C±Cl) A 00 , 1096, r t(CH2) A 00 , 767, r r(CH2) ?A, 932, r (CH2)
?A, 587, r (O±H) A 0 , 830, d (C±H) ?A, 820, r t(C±H) A 0 , 1329, d (C±H)
A 0 , 1412, d (CH2) A 00 , 1044, r t(CH2) ?A, 493, d (C±H) A 00 , 934, r r(CH2) A 0 , 654, d (CH2) ?A, 714, n (C±Cl)
Table 3 Harmonic vibrational modes of species in the reaction (B3LYP/6-31111G pp)
B2, 2942, n a(CH2)
?A, 853, r (C±H) A 0 , 1335, d (C±H) ?A, 1252, n (C±O) A 0 , 3054, n (C±H)
A 00 , 3326, n as(CH2) A 0 , 1244, p (CH2) ?A, 983, r (CH2) A 0 , 1404, d S(CH2) A 0 , 779, n (C±Cl) ?A, 1192, n (C±O)
?A, 1325, d (C±H) A 0 , 1556, n (C±O) ?A, 1365, d (C±H)
A 0 , 1306, d (CH2) ?A, 1291, d (C±H) A 0 , 1450, n (C±O) A 0 , 1839, n (C±O) ?A, 1279, d (C±H)
?A, 1643, n (C±O) A 0 , 2270, n (O±H) ?A, 3190, n (C±H)
A 0 , 2913, n S(CH2) ?A, 1745, n (C±O) A 0 , 2980, n S(CH2) A 00 , 2110, n S(CH2) ?A, 2393, n (C±H)
?A, 3095, n (C±H) A 0 , 2961, n (C±H) ?A, 3790, n (O±H)
A 00 , 2943, n as(CH2) ?A, 3035, n (C±H) A 00 , 3088, n as(CH2) A 0 , 3488, n as(CH2) ?A, 3104, n (C±H)
Z. Zhou et al. / Journal of Molecular Structure (Theochem) 579 (2002) 21±29 25
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Z. Zhou et al. / Journal of Molecular Structure (Theochem) 579 (2002) 21±29
produce a stable intermediate, the other four modes generated the same intermediate, OCH2Cl (IM1). Based on IM1, six transitions and another intermediate were found. Equilibrium geometries of all species are given in Fig. 2. Each transition has only one imaginary frequency, which indicates that all of them really exist. Through IRC calculation, the six transitions are con®rmed and connected with relevant reactants and products, respectively.
3.4. Analysis of the vibrational modes and vibrational frequencies The vibrational frequencies of the same radical might increase or decrease slightly because of different chemistry environment in various compounds. The relationship between the force constants of bond fi and the vibrational frequencies vi can be represented as fi 4pmc2 v2i
3.2. Potential energies of all species in the reaction The potential energy surface for the reaction O( 3P) with CH2Cl radical was explored using B3LYP/631111G pp method, which is found to an inexpensive and reliable method by comparing the results in the paper with those of G2MP method and experimental values [5]. The energies of various stationary points are listed in Table 2. In addition, the overall energetic pro®le based on the B3LYP energies for the reaction of O( 3P) with CH2Cl is shown in Fig. 3. An association±elimination mechanism for the reaction is obvious, as shown in Fig. 3. Meanwhile, six channels of the reaction were easily found. 3.3. Assignment of the vibration modes The reactant, CH2Cl, belongs to the Cs point group and the two hydrogen atoms are symmetrical with respect to the plane containing chlorine and carbon atoms. According to the fundamental vibrational modes of 3n 2 6; in nonlinear molecules, there are three stretching vibrational modes and three bending vibrational modes. Three characteristic vibration modes of methylene appeared in vibrational modes of CH2Cl. These are bending in plane d (CH2), symmetry stretch n s(CH2) and asymmetry stretch n as(CH2) and their frequencies are 1412.4, 3168.6 and 3325.7 cm 21, respectively. Because the reduced mass of C±Cl is greater than that of C±H, its stretching vibration frequency is much lower than that of latter, which elucidates the inverse proportion between vibration frequencies and reduced mass. According to the vibrational modes of CH2Cl and available experimental values, the vibration modes of intermediates, transitions and products are assigned and listed in Table 3.
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where m is the reduced mass and c is the velocity of light. If vi of the special radical increases, the fi also increases and the bond length decreases; on the contrary, when vi decreases, the fi reduces, and the bond length increases. The information about the bond formation and bond rupture is in close relationship with above parameters. According to the conclusion, analyzing the changes in vibrational modes from reactant to transitions and from transitions to products can elucidate the direction of reactions and degree of chemical reaction. Therefore, the reaction mechanism may be clear-cut. Following the reactions are explained by using vibrational modes and vibrational frequencies one by one. 3.4.1. O 1 CH2Cl ! OCH2Cl (IM1) reaction When an O atom connects with C atom in CH2Cl to become OCH2Cl (IM1), and it belongs to the Cs point group, to which the reactant CH2Cl belongs, compared to CH2Cl, three modes of normal vibration are added, which are C±O stretch (n (C±H)), C±O inplane (d (C±O)) and H±C±H out-plane (p (CH2)). Because of the effect of oxygen atom, the symmetrical and asymmetrical stretching vibrational frequencies are red shifted from 3168.6 to 2912.8 cm 21 and from 3325.7 to 2943.0 cm 21, respectively. In ®ngerprint region (400±1300 cm 21), the vibrational frequencies of C±Cl bond stretching and H±C±H bending out-plane also vary. The energy of IM1 is much lower than that of O 1 CH2Cl due to great changes in vibrational modes and frequencies. The reaction is irreversible. 3.4.2. IM1 ! TS1 ! H 1 OCHCl reaction Much important information can be found through comparing the vibrational modes and frequencies of intermediate with those of TS1. When one C±H bond is lengthened in the transition state TS1, there are
Z. Zhou et al. / Journal of Molecular Structure (Theochem) 579 (2002) 21±29
great changes in all the vibrational modes of H±C±H. H±C±H symmetry stretching and asymmetry stretching vanish; two C±H stretching vibrational modes are produced, in which the stretching vibrational frequencies of the lengthened C±H bond become imaginary values (2859.8 cm 21). The imaginary frequency means that the interaction between C and H is very weak and the H atom is departing from the molecule; all bending vibrational frequencies of H±C±H are descent. On the contrary, it can be seen from Table 3 that the vibrational frequencies of C±Cl bond stretch and C±O bond stretch were blue shifted from 654.0 to 685.0 cm 21 and from 1138.9 to 1745.4 cm 21, respectively. In the mass, the molecular vibrational frequencies were red shifted, thus the corresponding force constants are decreased in the transition state TS1 according to Eq. (8), which indicates that the transition state TS1 was unstable in energy. Although the same atoms are present in IM1 and TS1, they are not the same species resulting from the different vibration modes and frequencies in ®ngerprint region. When the transition state TS1 is contrasted with the product OCHCl, it is evident that the imaginary frequency of C±H was vanished and the vibrational frequencies of other vibration modes were blue shifted correspondingly. These results mean that the force constants of all vibration modes were increased and the product is stable in energy. This is a C±H bond cleavage reaction and the barrier height is 2109.6 kJ mol 21. Due to the transition state TS1's product-like structure, the direction of the reaction is largely determined by the molecular vibrational energy. 3.4.3. IM2 ! TS2 ! Cl 1 CH2O reaction With the C±Cl bond lengthening, IM1 is becoming transition state TS2 that possess the same point group, Cs : Evidently, it can be founded from Table 2 that the vibrational frequency of C±Cl bond stretching mode has greatly fallen from 654.0 to 21309.2 cm 21. All vibrational frequencies except C±O bond bending mode have raised more or less: C±H symmetrical and asymmetrical stretching vibration frequencies blue shift by 66.8 and 144.8 cm 21, respectively; C± O bond stretching vibrational frequency ranges from 1138.9 to 1449.9 cm 21. As a whole, the vibrational frequencies are red shifted; therefore, the force constants decrease. Comparing with the above reac-
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tion channel, the changes in vibration frequencies in this channel are smaller than those of the above channel, which may be used to explain the various barrier heights. The greater the changes are, the higher the barrier height is. According to this conclusion, the barrier height of this channel is the lowest one of all channels and it is the only one channel. This agrees with the experimental results. As the C±Cl ruptured, the imaginary frequencies naturally disappeared. In products, the force constants of all vibrational modes increased and it indicates the products are stable. 3.4.4. IM1 ! TS3 ! H2 1 ClO reaction Because the two C±H bonds lengthen simultaneously, transition state TS3 also belongs to Cs point group. However, the vibrational frequencies of CH2 radical have large varieties. The frequencies of H±C±H rock out-plane reduce to 2809.4 cm 21, which means that the interaction between C and H weakened. In addition, other frequencies of H±C±H vibrational modes also are red shifted a lot, for example, the frequency of H±C±H bending in-plane is 1306.1 cm 21 in IM1 but they fall to 654.2 cm 21 in TS3 and the difference is more than 650.0 cm 21. Except for the H±C±H asymmetry stretching mode and C±O bond stretching mode and C±Cl bond stretching mode, the other vibrational modes have considerably decreased. The very difference of frequencies between IM1 and TS3 results in the highest barrier height in all channels and at the same time, indicates that TS3 is quite unstable. 3.4.5. IM1 ! TS4 ! IM2 reactions IM1 can isomerize to another intermediate CHClOH (IM2) via the 1,2-H shift transition state TS4. When H atom twists to O atom in the TS4, the bending vibrational mode of C±H, greatly decreased from 1306.1 to 22020.8 cm 21, the stretching vibrational mode of C±H also reduced from 2912.7 to 2392.9 cm 21. However, the stretching vibrational mode of C±O and C±Cl, are blue shifted slowly. Considering all changes of vibrational mode of the species, the reduced values are much higher than the increased, which lead to the high un-stability of TS4. It is obvious that the imaginary frequency of C±H vanished and the vibration modes of O±H were produced when vibrational modes and vibrational
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Z. Zhou et al. / Journal of Molecular Structure (Theochem) 579 (2002) 21±29
frequencies of TS4 are compared with those of IM2. These results con®rm that C±H has been ruptured and O±H has been formed. IM2 and TS4 have no symmetry. The energy of IM2 is 27.384 kJ mol 21 lower than IM1, thus IM2 is a more stable intermediate and can further decompose. 3.4.6. Decomposition reaction of IM2 Three decomposition channels of IM2 have been found; C±O bond cleavage leading to the formation of CHCl 1 OH, O±H bond cleavage leading to H 1 CHClO via transition state TS5, and the formation of HCl 1 HCO via four-center transition state TS6. The ®rst channel undergoes no transition state and directly creates products. Because the energy of products is higher than that of IM2, the reaction is endothermic. IM2 and TS5 have no symmetry. As H atom is apart from O atom in TS5, the stretching vibrational mode of O±H are momentarily decreased from 3790.0 to 21259.6 cm 21. Compared to IM2, the vibrational modes of TS5 have no frame vibrational mode, which appeared in IM2 and the bending mode of Cl±C±O (456.8 cm 21). The imaginary frequency of O±H stretching mode disappeared at the time of H±O bond rupture. The vibrational force constants in product OCHCl are higher than that in TS5, which can explain the stability of product. H atom twist to Cl atom in the transition state TS6, then all atoms of TS6 are in the same plane. Resulting from these, the molecular vibrational modes altering the stretching vibrational frequency of O±H bond was reduced to as much as 1520.4 cm 21 and the deformational vibrational frequencies of H±O±C is 2436.4 cm 21. Simultaneously, the vibrational frequencies of C±H bond stretching and bending are red shifted from 3189.5 to 2960.7 cm 21, from 1365.1 to 1335.3 cm 21 and from 452.1 to 270.8 cm 21, respectively. For these, TS6 is less stable than TS5 and the barrier height with respect to IM2 of this channel is higher than that of TS5. From the result, it is obvious that IM2 decomposes usually via TS5 and produce H 1 OCHCl. 3.5. Electron transfer reaction Through the analysis of vibrational modes and vibrational frequencies, the reaction includes bond rupture, bond formation and isomerization and the
electron transfer take part in the intra-molecule at the same time, can be obtained. According to the Frank±Condon theory [9,10], the contact distance and the momentum of atomic nucleus are all unchangeable in one electron transfer process. It took 10 216 s for the electron transfer to complete. Because electron transfer makes the reorganization in whole molecule structure, the reorganization energies come over not only the energies of bond cleavage or formation but also the complete molecular vibrational modes. By the time the intermediate transfers to transition state, the electron transfer takes place and then the molecule takes part in reorganization. At the same time, the vibrational modes and vibrational frequencies of different radicals also have changed more or less, which may be elucidated from the various electronic ground states of dissimilar species. Through the analysis on the vibrational modes and vibrational frequencies of reactant, intermediates, transition states and products, a quantitative analysis was provided on the reaction mechanism. 4. Conclusions The studies of the reaction, O( 3P) 1 CH2Cl are performed using DFT method. The detailed association±elimination mechanism of the reaction O( 3P) 1 CH2Cl is analyzed in terms of the changes in vibrational modes and vibrational frequencies of the stationary points on the calculated B3LYP potential energy surface. It can be drawn from this study that, H 1 CHClO are the major products and Cl 1 CH2O are the minor products. The mechanisms are in good agreement with the experimental results. Acknowledgements Project supported by the Natural Science Foundation of Shandong Province (Y99B01), the National Key Laboratory Foundation of Crystal Material and the National Natural Science Foundation of China (No. 2967305). References [1] S.M. Senkan, Environ. Sci. Technol. 22 (1998) 2368.
Z. Zhou et al. / Journal of Molecular Structure (Theochem) 579 (2002) 21±29 [2] E.R. Altwichker, J.S. Schonberg, R.K.N.Y. Konduri, M.S. Milligan, Hazard, Waste Hazard. Mater. 7 (1990) 73. [3] J.A. Seetular, I.R. Slagle, D. Gutman, et al., Kinetics of the reaction of the CH3 radical with oxygen atoms, Chem. Phys. Lett. 252 (1996) 299±303. [4] J.A. Seetular, I.R. Slagle, Kinetics of the CH2Cl radical with oxygen atoms, Chem. Phys. Lett. 277 (1997) 381±386. [5] Baoshan Wang, Hua Hou, Yushu Gu, J. Phys. Chem. A 103 (1999) 2062±2065.
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[6] Xiaolan Wang. Organic chemistry, 2nd ed (Chinese), Higher Edu. Press. 1985. [7] Zhengyu Zhou, Aiping Fu, Dongmei Du, J. Chin. Chem. 3 (2000) 297. [8] Zhengyu Zhou, Dongmei Du, Aiping Fu, Vib. Spectrosc. 23 (2000) 143. [9] H. Taube, Angew. Chem. 23 (1984) 329. [10] J.O'M. Bockris, S.U.M. Khan, Quantum Electrochemistry, Pasnm Press, New York, 1979 Chapter 4.
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Theoretical studies on O( 3P) 1 CH2Cl reaction mechanism Zhengyu Zhou a,b,*, Li Guo a, Chengxue Li a, Hongwei Gao a b
a Department of Chemistry, Qufu Normal University, Qufu, Shandong 273165, People's Republic of China State Key Laboratory Crystal Materials Shandong University, Shandong, Jinan 250100, People's Republic of China
Received 1 July 2001; accepted 1 August 2001
Abstract The reaction of oxygen atom with chlorinated methyl radical has been studied using density functional theory (DFT) method at 6-31111G pp level. All the geometries, vibrational frequencies and energies of different stationary points are calculated by B3LYP/6-31111G pp and the results agree with the experimental values. The vibrational frequencies and modes of the reactant, intermediates, transition states and products have been calculated, the changes of these frequencies and modes analyzed and the changes in the vibrational force constants are assigned. The relationship and the change among them can con®rm the mechanism of the reaction and the process of electron transfer. Through the analysis, the major and minor reaction channels are con®rmed. A new study method of analyzing reaction mechanism is presented. q 2002 Elsevier Science B.V. All rights reserved. Keywords: Reaction mechanism; DFT theory; Poly channels reaction; CH2Cl free radical
1. Introduction During the rupture of hydrocarbon, some radicals are often produced, which play an important role in species of the products of combustion process (especially the radicals of the rupture of methane) and have recently been paid much attention. Incineration is an effective method for the management of halogenated hydrocarbon wastes [1,2]. How to control secondary pollution during the incineration is an important subject [3] and becomes a focus for environment chemistry and kinetics chemistry. In order to control pollution effectively, it is necessary to carry out studies of the reaction mechanism. Halogenated methyl is highly reactive when halogen atoms substitute the hydrogen atoms in the * Corresponding author. Address: Department of Chemistry, Qufu Normal University, Qufu, Shandong 273165, People's Republic of China. Tel.: 186-537-445-5474; fax: 186-537-445-8276. E-mail address: [email protected] (Z. Zhou).
methyl. Oxygen atoms O( 3P) can rapidly react with halogenated methyls and the reactions are highly exothermic. The reaction of O( 3P) with CH2Cl is more important in combustion reactions of halogenated polymers. Until date, there are only few experimental and theoretical studies on this type of reactions. Until 1997, Seetula et al. [4] used a heatable tubular reactor coupled with a photoionization mass spectrometer to obtain the overall rate constants of the reaction of oxygen atoms with chlorinated methyl radicals. CHClO and CH2O were found to be the major products and were found to generate from the decomposition of an energy rich intermediate, OCH2Cl. On one hand, the results are used for reference to control of the environmental pollution; on the other hand, they are of great importance being a part of reaction mechanism. Recently, Baoshan Wang et al. studied the reaction of O( 3P) with CH2Cl and presented the following mechanism [5] O 1 CH2 Cl ! OCH2 Cl IM1 ! H 1 CHClO
0166-1280/02/$ - see front matter q 2002 Elsevier Science B.V. All rights reserved. PII: S 0166-128 0(01)00708-4
1
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Z. Zhou et al. / Journal of Molecular Structure (Theochem) 579 (2002) 21±29
Table 1 Ê , bond angles in degree and frequency in cm 21) Geometry, vibrational frequencies of reactant (CH2Cl) (bond length in A Method
HF
BLYP
B3LYP
B3P86
UMP2
QCISD
Energy R(C±Cl) R(C±H) /CClH /HCH v 1(A 0 ) v 2(A 0 ) v 3(A 00 ) v 4(A 0 ) v 5(A 0 ) v 6(A 00 )
2498.4996 1.7213 1.0707 116.4 122.9 468.9 858.1 1078.4 1523.6 3300.2 3452.4
2499.4422 1.729 1.0839 117.4 125.2 178.3 791.0 974.8 1372.5 3092.4 3247.8
2499.4818 1.7137 1.0776 117.5 124.9 185.4 826.4 1001.5 1412.4 3168.6 3325.7
2499.9469 1.7015 1.0781 117.6 124.7 226.5 852.4 1001.8 1412.2 3180.6 3337.6
2498.8326 1.6982 1.0774 117.56 123.8 242.8 882.6 1048.2 1474.3 3238.4 3392.5
2498.4993 1.7085 1.0805 117.6 123.7 222.4 862.3 1033.5 1459.8 3194.9 3342.9
O 1 CH2 Cl ! OCH2 Cl IM1 ! Cl 1 CH2 O
2
O 1 CH2 Cl ! OCH2 Cl IM1 ! H2 1 ClCO
3
O 1 CH2 Cl ! OCH2 Cl IM1 ! CHClOH IM2 4 O 1 CH2 Cl ! OCH2 Cl IM1 ! CHClOH IM2 ! H 1 CHClO
5
O 1 CH2 Cl ! OCH2 Cl IM1 ! CHClOH IM2 ! HCl 1 HCO
6
on structures, energies and force constants are obviously superior to results of small basis sets. At ®rst, the geometries of reactants and products are optimized at various theoretical methods such as HF, UMP2, BLYP, B3LYP, B3P86, respectively. B3LYP method is found superior to the other methods through comparison of the theoretical results with the experimental ones. Then we optimize geometries of two intermediates and six transition, which are con®rmed through IRC calculation by using B3LYP/ 6-31111G pp method, at the same time, we calculate ZPE of the stationary points on the basis of the optimized structures. All calculations were performed using the gaussian 94 program package.
O 1 CH2 Cl ! OCH2 Cl IM1 ! CHClOH IM2 ! H2 1 ClCO
7
Further, they analyzed the mechanism in terms of the changes in the energies and bond length of various species. Density functional theory (DFT) studies of this reaction are carried out in this paper. This reaction on the lowest-lying double potential energy surface using DFT methods is examined and the vibrational frequencies and vibrational modes of all species for the reaction are analyzed. The reaction mechanism is explicitly illustrated in detail. 2. Computation methods DFT methods at the 6-31111G pp basis set are used throughout in this paper. The basis set was chosen on the basis of the ®ndings that the 6-31111G pp results
3. Results and discussion 3.1. Optimized geometries of reactants, intermediates, transition and products The geometry of the reactant, CH2Cl, is optimized by HF, BLYP, B3LYP, B3P86, UMP2 and QCISD theory methods, respectively. The bond lengths, bond angles, vibrational frequencies and vibrational modes are listed in Table 1. The experimental values of the reactant (CH2Cl) geometry are not available, but its geometry can be determined semi-qualitatively through analyzing its bonding possibility, comparing with related or similar species such as methane (CH4), chloromethane (CH3Cl) and dichloromethane (CH2Cl2). Methane belongs to Td point group and its C±H length is
Z. Zhou et al. / Journal of Molecular Structure (Theochem) 579 (2002) 21±29
23
Fig. 1. Attacking modes of O( 3P).
Ê and bond angles in degree). Fig. 2. B3LYP/6-31111G pp optimized geometries of the various isomers of the reaction (bond lengths in A
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Z. Zhou et al. / Journal of Molecular Structure (Theochem) 579 (2002) 21±29
Table 2 Total energies and the relative energies of various species (B3LYP/ 6-31111G pp) (total energies in Hartree and relative energies in kJ mol 21) Species
Total energies
DH
O 1 CH2Cl Cl 1 CH2O H 1 CHClO H2 1 ClCO HCl 1 HCO OH 1 CHCl IM1 IM2 TS1 TS2 TS3 TS4 TS5 TS6
2574.5490919 2574.68222 2574.669367 2574.694067 2574.705718 2574.547271 2574.695112 2574.703733 2574.660723 2574.661234 2574.596289 2574.644592 2574.656712 2574.64822
0.0 2349.529 2315.783 2380.634 2411.223 0.005 2383.377 2406.012 2293.088 2294.430 2114.465 2250.737 2282.558 2260.262
DH expt: 2358.2 2391.6 2420.9
Ê the bond angles(/HCH) 109.58 [6]. The C±H 1.09 A Ê [6] and C±Cl length is length reduces to 1.08 A Ê in chloromethane, which belongs to C3v 1.776 A point group. Table 1 shows the C±H length ranging Ê , C±Cl length 1.70±1.73 A Ê, from 1.07 to 1.084 A which are calculated by HF and DFT methods. The results aforementioned are lower than those of methane and chloromethane because of the space
effect and inducing-effect of chlorine atom, which agrees with the experimental rules and elucidates the rationality of theoretical calculations. It can also be found in Table 1 that the predicted vibrational frequencies of HF are in worst agreement with the calculated results. There is a large overestimation of the frequencies at HF level, even the scale factors (0.89) considered the results are still worse than DFT methods, which may be due to the slightly too short bond lengths resulting from neglecting electron correlation in the theory. The results of various DFT methods are a little identical and agree well with experimental values, especially, the B3LYP is superior to other methods for predicting molecular properties and vibration frequencies. QCISD, which includes the con®guration interaction, is theoretically more accurate but it needs more time to predict. The conclusion has been recently reported in our papers [7,8]. According to aforesaid, the B3LYP/631111G pp method is chosen for optimizing geometries and predicting vibrational frequencies of all species in the reaction. According to our assumption, oxygen atom, O( 3P), has ®ve modes of attacking at the reactant, CH2Cl. It can approach CH2Cl from different atoms, like C, H and Cl atom, and from different directions. Fig. 1 shows all the modes. Except mode (3), which cannot
Fig. 3. Overall pro®le of potential energy surface for the reaction of O( 3P) with CH2Cl calculated at B3LYP level of theory.
A 0 , 786, n (C±Cl)
A 0 , 1233, d (C±H)
?A, 214, p (O±H) ?A, 271, p (C±H) ?A, 452, r (C±H) A 0 , 720, n (C±Cl) A 0 , 582, n (C±Cl) B2, 1260, r r(CH2)
?A, i1259.6, n (O±H) A 0 , i436.4, d (O±H) ?A, 367, r (O±H) A 0 , 448, d (O±C±Cl) A 0 , 335, d Cl±C±O) B1, 1202, r W(CH2)
TS5 TS6 IM2 COClH COCl COHH
CClO
A 0 , 826, n (C±Cl) A 0 , 650, r W(CH2) ?A, 379, p (C±H) A 0 , 256, d (C±O) A 0 , 480, d (C±O) ?A, 406, d (O±C±Cl)
A 0 , 185, r w(CH2) A 0 , 384, d (C±O) ?A, i859.8, n (C±H) A 0 , i1309.2, n (C±Cl) A 0 , i809.4, r W(CH2) ?A, i2020.8, d (C±H)
Sym. Freq. Assig. IM1 TS1 TS2 TS3 TS4
Reactant
Species
A 0 , 2897, n (C±H)
?A, 457, d (Cl±C±0) ?A, 310, Ringvib ?A, 669, n (C±Cl) A 00 , 948, p (C±H) A 0 , 1955, n (C±O) A1, 1531, d (CH2)
A 00 , 1002, r t(CH2) A 0 , 654, n (C±Cl) ?A, 434, p (C±H) A 0 , 871, r W(CH2) A 00 , 514, r t(CH2) ?A, 598, d (C±H) ?A, 739, n (C±Cl) A 00 , 1130, p (O±H) ?A, 1164, Framevi A 0 , 1855, n (C±O) A1, 2885, n s(CH2)
A1, 1815, n (C±O)
A 0 , 3181, n S(CH2) A 0 , 1139, n (C±O) ?A, 685, n (C±Cl) A 00 , 1096, r t(CH2) A 00 , 767, r r(CH2) ?A, 932, r (CH2)
?A, 587, r (O±H) A 0 , 830, d (C±H) ?A, 820, r t(C±H) A 0 , 1329, d (C±H)
A 0 , 1412, d (CH2) A 00 , 1044, r t(CH2) ?A, 493, d (C±H) A 00 , 934, r r(CH2) A 0 , 654, d (CH2) ?A, 714, n (C±Cl)
Table 3 Harmonic vibrational modes of species in the reaction (B3LYP/6-31111G pp)
B2, 2942, n a(CH2)
?A, 853, r (C±H) A 0 , 1335, d (C±H) ?A, 1252, n (C±O) A 0 , 3054, n (C±H)
A 00 , 3326, n as(CH2) A 0 , 1244, p (CH2) ?A, 983, r (CH2) A 0 , 1404, d S(CH2) A 0 , 779, n (C±Cl) ?A, 1192, n (C±O)
?A, 1325, d (C±H) A 0 , 1556, n (C±O) ?A, 1365, d (C±H)
A 0 , 1306, d (CH2) ?A, 1291, d (C±H) A 0 , 1450, n (C±O) A 0 , 1839, n (C±O) ?A, 1279, d (C±H)
?A, 1643, n (C±O) A 0 , 2270, n (O±H) ?A, 3190, n (C±H)
A 0 , 2913, n S(CH2) ?A, 1745, n (C±O) A 0 , 2980, n S(CH2) A 00 , 2110, n S(CH2) ?A, 2393, n (C±H)
?A, 3095, n (C±H) A 0 , 2961, n (C±H) ?A, 3790, n (O±H)
A 00 , 2943, n as(CH2) ?A, 3035, n (C±H) A 00 , 3088, n as(CH2) A 0 , 3488, n as(CH2) ?A, 3104, n (C±H)
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Z. Zhou et al. / Journal of Molecular Structure (Theochem) 579 (2002) 21±29
produce a stable intermediate, the other four modes generated the same intermediate, OCH2Cl (IM1). Based on IM1, six transitions and another intermediate were found. Equilibrium geometries of all species are given in Fig. 2. Each transition has only one imaginary frequency, which indicates that all of them really exist. Through IRC calculation, the six transitions are con®rmed and connected with relevant reactants and products, respectively.
3.4. Analysis of the vibrational modes and vibrational frequencies The vibrational frequencies of the same radical might increase or decrease slightly because of different chemistry environment in various compounds. The relationship between the force constants of bond fi and the vibrational frequencies vi can be represented as fi 4pmc2 v2i
3.2. Potential energies of all species in the reaction The potential energy surface for the reaction O( 3P) with CH2Cl radical was explored using B3LYP/631111G pp method, which is found to an inexpensive and reliable method by comparing the results in the paper with those of G2MP method and experimental values [5]. The energies of various stationary points are listed in Table 2. In addition, the overall energetic pro®le based on the B3LYP energies for the reaction of O( 3P) with CH2Cl is shown in Fig. 3. An association±elimination mechanism for the reaction is obvious, as shown in Fig. 3. Meanwhile, six channels of the reaction were easily found. 3.3. Assignment of the vibration modes The reactant, CH2Cl, belongs to the Cs point group and the two hydrogen atoms are symmetrical with respect to the plane containing chlorine and carbon atoms. According to the fundamental vibrational modes of 3n 2 6; in nonlinear molecules, there are three stretching vibrational modes and three bending vibrational modes. Three characteristic vibration modes of methylene appeared in vibrational modes of CH2Cl. These are bending in plane d (CH2), symmetry stretch n s(CH2) and asymmetry stretch n as(CH2) and their frequencies are 1412.4, 3168.6 and 3325.7 cm 21, respectively. Because the reduced mass of C±Cl is greater than that of C±H, its stretching vibration frequency is much lower than that of latter, which elucidates the inverse proportion between vibration frequencies and reduced mass. According to the vibrational modes of CH2Cl and available experimental values, the vibration modes of intermediates, transitions and products are assigned and listed in Table 3.
8
where m is the reduced mass and c is the velocity of light. If vi of the special radical increases, the fi also increases and the bond length decreases; on the contrary, when vi decreases, the fi reduces, and the bond length increases. The information about the bond formation and bond rupture is in close relationship with above parameters. According to the conclusion, analyzing the changes in vibrational modes from reactant to transitions and from transitions to products can elucidate the direction of reactions and degree of chemical reaction. Therefore, the reaction mechanism may be clear-cut. Following the reactions are explained by using vibrational modes and vibrational frequencies one by one. 3.4.1. O 1 CH2Cl ! OCH2Cl (IM1) reaction When an O atom connects with C atom in CH2Cl to become OCH2Cl (IM1), and it belongs to the Cs point group, to which the reactant CH2Cl belongs, compared to CH2Cl, three modes of normal vibration are added, which are C±O stretch (n (C±H)), C±O inplane (d (C±O)) and H±C±H out-plane (p (CH2)). Because of the effect of oxygen atom, the symmetrical and asymmetrical stretching vibrational frequencies are red shifted from 3168.6 to 2912.8 cm 21 and from 3325.7 to 2943.0 cm 21, respectively. In ®ngerprint region (400±1300 cm 21), the vibrational frequencies of C±Cl bond stretching and H±C±H bending out-plane also vary. The energy of IM1 is much lower than that of O 1 CH2Cl due to great changes in vibrational modes and frequencies. The reaction is irreversible. 3.4.2. IM1 ! TS1 ! H 1 OCHCl reaction Much important information can be found through comparing the vibrational modes and frequencies of intermediate with those of TS1. When one C±H bond is lengthened in the transition state TS1, there are
Z. Zhou et al. / Journal of Molecular Structure (Theochem) 579 (2002) 21±29
great changes in all the vibrational modes of H±C±H. H±C±H symmetry stretching and asymmetry stretching vanish; two C±H stretching vibrational modes are produced, in which the stretching vibrational frequencies of the lengthened C±H bond become imaginary values (2859.8 cm 21). The imaginary frequency means that the interaction between C and H is very weak and the H atom is departing from the molecule; all bending vibrational frequencies of H±C±H are descent. On the contrary, it can be seen from Table 3 that the vibrational frequencies of C±Cl bond stretch and C±O bond stretch were blue shifted from 654.0 to 685.0 cm 21 and from 1138.9 to 1745.4 cm 21, respectively. In the mass, the molecular vibrational frequencies were red shifted, thus the corresponding force constants are decreased in the transition state TS1 according to Eq. (8), which indicates that the transition state TS1 was unstable in energy. Although the same atoms are present in IM1 and TS1, they are not the same species resulting from the different vibration modes and frequencies in ®ngerprint region. When the transition state TS1 is contrasted with the product OCHCl, it is evident that the imaginary frequency of C±H was vanished and the vibrational frequencies of other vibration modes were blue shifted correspondingly. These results mean that the force constants of all vibration modes were increased and the product is stable in energy. This is a C±H bond cleavage reaction and the barrier height is 2109.6 kJ mol 21. Due to the transition state TS1's product-like structure, the direction of the reaction is largely determined by the molecular vibrational energy. 3.4.3. IM2 ! TS2 ! Cl 1 CH2O reaction With the C±Cl bond lengthening, IM1 is becoming transition state TS2 that possess the same point group, Cs : Evidently, it can be founded from Table 2 that the vibrational frequency of C±Cl bond stretching mode has greatly fallen from 654.0 to 21309.2 cm 21. All vibrational frequencies except C±O bond bending mode have raised more or less: C±H symmetrical and asymmetrical stretching vibration frequencies blue shift by 66.8 and 144.8 cm 21, respectively; C± O bond stretching vibrational frequency ranges from 1138.9 to 1449.9 cm 21. As a whole, the vibrational frequencies are red shifted; therefore, the force constants decrease. Comparing with the above reac-
27
tion channel, the changes in vibration frequencies in this channel are smaller than those of the above channel, which may be used to explain the various barrier heights. The greater the changes are, the higher the barrier height is. According to this conclusion, the barrier height of this channel is the lowest one of all channels and it is the only one channel. This agrees with the experimental results. As the C±Cl ruptured, the imaginary frequencies naturally disappeared. In products, the force constants of all vibrational modes increased and it indicates the products are stable. 3.4.4. IM1 ! TS3 ! H2 1 ClO reaction Because the two C±H bonds lengthen simultaneously, transition state TS3 also belongs to Cs point group. However, the vibrational frequencies of CH2 radical have large varieties. The frequencies of H±C±H rock out-plane reduce to 2809.4 cm 21, which means that the interaction between C and H weakened. In addition, other frequencies of H±C±H vibrational modes also are red shifted a lot, for example, the frequency of H±C±H bending in-plane is 1306.1 cm 21 in IM1 but they fall to 654.2 cm 21 in TS3 and the difference is more than 650.0 cm 21. Except for the H±C±H asymmetry stretching mode and C±O bond stretching mode and C±Cl bond stretching mode, the other vibrational modes have considerably decreased. The very difference of frequencies between IM1 and TS3 results in the highest barrier height in all channels and at the same time, indicates that TS3 is quite unstable. 3.4.5. IM1 ! TS4 ! IM2 reactions IM1 can isomerize to another intermediate CHClOH (IM2) via the 1,2-H shift transition state TS4. When H atom twists to O atom in the TS4, the bending vibrational mode of C±H, greatly decreased from 1306.1 to 22020.8 cm 21, the stretching vibrational mode of C±H also reduced from 2912.7 to 2392.9 cm 21. However, the stretching vibrational mode of C±O and C±Cl, are blue shifted slowly. Considering all changes of vibrational mode of the species, the reduced values are much higher than the increased, which lead to the high un-stability of TS4. It is obvious that the imaginary frequency of C±H vanished and the vibration modes of O±H were produced when vibrational modes and vibrational
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Z. Zhou et al. / Journal of Molecular Structure (Theochem) 579 (2002) 21±29
frequencies of TS4 are compared with those of IM2. These results con®rm that C±H has been ruptured and O±H has been formed. IM2 and TS4 have no symmetry. The energy of IM2 is 27.384 kJ mol 21 lower than IM1, thus IM2 is a more stable intermediate and can further decompose. 3.4.6. Decomposition reaction of IM2 Three decomposition channels of IM2 have been found; C±O bond cleavage leading to the formation of CHCl 1 OH, O±H bond cleavage leading to H 1 CHClO via transition state TS5, and the formation of HCl 1 HCO via four-center transition state TS6. The ®rst channel undergoes no transition state and directly creates products. Because the energy of products is higher than that of IM2, the reaction is endothermic. IM2 and TS5 have no symmetry. As H atom is apart from O atom in TS5, the stretching vibrational mode of O±H are momentarily decreased from 3790.0 to 21259.6 cm 21. Compared to IM2, the vibrational modes of TS5 have no frame vibrational mode, which appeared in IM2 and the bending mode of Cl±C±O (456.8 cm 21). The imaginary frequency of O±H stretching mode disappeared at the time of H±O bond rupture. The vibrational force constants in product OCHCl are higher than that in TS5, which can explain the stability of product. H atom twist to Cl atom in the transition state TS6, then all atoms of TS6 are in the same plane. Resulting from these, the molecular vibrational modes altering the stretching vibrational frequency of O±H bond was reduced to as much as 1520.4 cm 21 and the deformational vibrational frequencies of H±O±C is 2436.4 cm 21. Simultaneously, the vibrational frequencies of C±H bond stretching and bending are red shifted from 3189.5 to 2960.7 cm 21, from 1365.1 to 1335.3 cm 21 and from 452.1 to 270.8 cm 21, respectively. For these, TS6 is less stable than TS5 and the barrier height with respect to IM2 of this channel is higher than that of TS5. From the result, it is obvious that IM2 decomposes usually via TS5 and produce H 1 OCHCl. 3.5. Electron transfer reaction Through the analysis of vibrational modes and vibrational frequencies, the reaction includes bond rupture, bond formation and isomerization and the
electron transfer take part in the intra-molecule at the same time, can be obtained. According to the Frank±Condon theory [9,10], the contact distance and the momentum of atomic nucleus are all unchangeable in one electron transfer process. It took 10 216 s for the electron transfer to complete. Because electron transfer makes the reorganization in whole molecule structure, the reorganization energies come over not only the energies of bond cleavage or formation but also the complete molecular vibrational modes. By the time the intermediate transfers to transition state, the electron transfer takes place and then the molecule takes part in reorganization. At the same time, the vibrational modes and vibrational frequencies of different radicals also have changed more or less, which may be elucidated from the various electronic ground states of dissimilar species. Through the analysis on the vibrational modes and vibrational frequencies of reactant, intermediates, transition states and products, a quantitative analysis was provided on the reaction mechanism. 4. Conclusions The studies of the reaction, O( 3P) 1 CH2Cl are performed using DFT method. The detailed association±elimination mechanism of the reaction O( 3P) 1 CH2Cl is analyzed in terms of the changes in vibrational modes and vibrational frequencies of the stationary points on the calculated B3LYP potential energy surface. It can be drawn from this study that, H 1 CHClO are the major products and Cl 1 CH2O are the minor products. The mechanisms are in good agreement with the experimental results. Acknowledgements Project supported by the Natural Science Foundation of Shandong Province (Y99B01), the National Key Laboratory Foundation of Crystal Material and the National Natural Science Foundation of China (No. 2967305). References [1] S.M. Senkan, Environ. Sci. Technol. 22 (1998) 2368.
Z. Zhou et al. / Journal of Molecular Structure (Theochem) 579 (2002) 21±29 [2] E.R. Altwichker, J.S. Schonberg, R.K.N.Y. Konduri, M.S. Milligan, Hazard, Waste Hazard. Mater. 7 (1990) 73. [3] J.A. Seetular, I.R. Slagle, D. Gutman, et al., Kinetics of the reaction of the CH3 radical with oxygen atoms, Chem. Phys. Lett. 252 (1996) 299±303. [4] J.A. Seetular, I.R. Slagle, Kinetics of the CH2Cl radical with oxygen atoms, Chem. Phys. Lett. 277 (1997) 381±386. [5] Baoshan Wang, Hua Hou, Yushu Gu, J. Phys. Chem. A 103 (1999) 2062±2065.
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[6] Xiaolan Wang. Organic chemistry, 2nd ed (Chinese), Higher Edu. Press. 1985. [7] Zhengyu Zhou, Aiping Fu, Dongmei Du, J. Chin. Chem. 3 (2000) 297. [8] Zhengyu Zhou, Dongmei Du, Aiping Fu, Vib. Spectrosc. 23 (2000) 143. [9] H. Taube, Angew. Chem. 23 (1984) 329. [10] J.O'M. Bockris, S.U.M. Khan, Quantum Electrochemistry, Pasnm Press, New York, 1979 Chapter 4.