numbers of studies were performed until very recently on the fundamental oxidation reaction mechanism of hydrogen sulfide and related H 9 S 9 O reaction systems.The oxidation process of H 2 S (and some times the catalytic effect of SO 2 ) have been investigated in several flame studies [1 -5], and the reaction mechanisms were discussed based on the measured product distributions. These studies have provided much useful information on the elementary reactions of H 9 S 9 O systems, however, it is generally very difficult to judge the reliability of kinetic/thermodynamic parameters of individual elementary reactions proposed in these indirect studies. It is also noted that even a conventional shock tube study was not performed for clarifying oxidation mechanism of H 2 S (as far as we know), except an ignition delay mea- INTRODUCTIONThe oxidation of hydrogen sulfide in combustion of fossil fuels and the consecutive atmospheric processes of sulfur oxides are creating serious pollution problems on a global scale.Many practical studies for reducing SO x in combustion systems have been conducted from the engineering point of view. In contrast, only very limited (1), the rate constants evaluated by numerical simulations are summarized as; k 1 ϭ 3.1 ϫ 10 Ϫ11 exp[Ϫ 75 kJ mol Ϫ1 /RT ] cm 3 molecule Ϫ1 s Ϫ1 (T ϭ 1400 -1850 K) with an uncertainty factor of about 2. Direct measurements of the rate constants for S ϩ O2 : SO ϩ O (2), and SO ϩ O 2 : SO 2 ϩ O (3) yield k 2 ϭ (2.5 Ϯ 0.6) ϫ 10 Ϫ11 exp[Ϫ(15.3 Ϯ 2.5) kJ mol Ϫ1 /RT ] cm 3 molecule Ϫ1 s Ϫ1 (T ϭ 980 -1610 K) and, k 3 ϭ (1.7 Ϯ 0.9) ϫ 10 Ϫ12 exp[Ϫ(34 Ϯ 11) kJ mol Ϫ1 /RT ] cm 3 molecule Ϫ1 s Ϫ1 (T ϭ 1130 -1640 K), respectively. By summarizing these data together with the recent experimental results on the H 9 S 9 O reaction systems, a new kinetic model for the H 2 S oxidation process is constructed. It is found that this simple reaction scheme is consistent with the experimental result on the induction time of SO 2 formation obtained by Bradley and Dobson.

Rate coefficients for deactivation of SO(X 3 Σ -, V ) 1-5) by collisions with SO 2 and nascent vibrational populations in V ) 0-2 in the photolysis of SO 2 at 193.3 nm have been determined. A single vibrational level of SO(X 3 Σ -) was detected with laser-induced fluorescence (LIF) excited via the B 3 Σ --X 3 Σsystem. Time-dependent profiles of LIF signals were recorded as a function of the pressures of SO 2 . Observed profiles were analyzed by the integrated-profiles method and reproduced well by convolution calculations. Overall rate coefficients for vibrational relaxation of SO(V) by SO 2 have been determined to be (4.7 ( 0.5) × 10 -12 (V ) 1), (6.7 ( 0.4) × 10 -12 (V ) 2), (7.2 ( 0.7) × 10 -12 (V ) 3), (6.1 ( 1.0) × 10 -12 (V ) 4), and (8.6 ( 0.7) × 10 -12 (V ) 5) in units of cm 3 molecule -1 s -1 (the quoted errors are 2σ). We have also found that 63% of the vibrational deactivations of V ) 2 by SO 2 are governed by double-quantum relaxation: (4.2 ( 0.9) × 10 -12 cm 3 molecule -1 s -1 for V ) 2 f V ) 0 and (2.5 ( 0.9) × 10 -12 cm 3 molecule -1 s -1 for V ) 2 f V ) 1. Ab initio calculations enable us to find two stable complexes: OS-OSO and SO-SO 2 , indicating that attractive interactions play a significant role in the relaxation. The nascent vibrational distributions of SO have been measured to be 0.52 ( 0.1/0.75 ( 0.1/1.0 for V ) 0/1/2. The differences in vibrational distributions reported by bulk and beam experiments are attributed to the difference in the temperature of parent SO 2 .

To date only one product, biphenyl, has been reported to be produced from C(6)H(5) + C(6)H(6)/C(6)H(5) reactions. In this study, we have investigated some unique products of C(6)H(5) + C(6)H(6)/C(6)H(5) reactions via both experimental observation and theoretical modeling. In the experimental study, gas-phase reaction products produced from the pyrolysis of selected aromatics and aromatic/acetylene mixtures were detected by an in situ technique, vacuum ultraviolet (VUV) single photon ionization (SPI) time-of-flight mass spectrometry (TOFMS). The mass spectra revealed a remarkable correlation in mass peaks at m/z = 154 {C(12)H(10) (biphenyl)} and m/z = 152 {C(12)H(8) (?)}. It also demonstrated an unexpected correlation among the HACA (hydrogen abstraction and acetylene addition) products at m/z = 78, 102, 128, 152, and 176. The analysis of formation routes of products suggested the contribution of some other isomers in addition to a well-known candidate, acenaphthylene, in the mass peak at m/z = 152 (C(12)H(8)). Considering the difficulties of identifying the contributing isomers from an observed mass number peak, quantum chemical calculations for the above-mentioned reactions were performed. As a result, cyclopenta[a]indene, as-indacene, s-indacene, biphenylene, acenaphthylene, and naphthalene appeared as novel products, produced from the possible channels of C(6)H(5) + C(6)H(6)/C(6)H(5) reactions rather than from their previously reported formation pathways. The most notable point is the production of acenaphthylene and naphthalene from C(6)H(5) + C(6)H(6)/C(6)H(5) reactions via the PAC (phenyl addition-cyclization) mechanism because, until now, both of them have been thought to be formed via the HACA routes. In this way, this study has paved the way for exploring alternative paths for other inefficient HACA routes using the PAC mechanism.

Thermal decomposition of COS was investigated by shock tubes between 1140—3230 K. The decay of COS and S was monitored by IR emissions and atomic resonance absorption spectrometry (ARAS) coupled with laser flash photolysis technique, respectively. The rate constants for the reactions COS + M → CO + S + M (1) and COS + S → CO + S2 (2) were determined as k1 = (4.07 ± 1.83) × 10−10exp (−257 ± 24kJ/RT), T: 1900—3230 K and k2 = (3.91 ± 1.18) × 10−11exp (−28.3 ± 0.9 kJ/RT) cm3 molecule−1 s−1, T: 1140—1680 K.

Isomer patterns of polychlorinated naphthalenes (PCNs), polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated biphenyls (PCBs), and polychlorinated dibenzofurans (PCDFs) from municipal waste incinerators (MWIs) were predicted by a model based on symmetry numbers and preferential chlorination positions. Fly ash isomer patterns from five stoker and seven fluidized bed incinerators were compared to validate the prediction model. The isomer patterns of the highly chlorinated PCN homologues from stoker type incinerators were successfully predicted. The relative equilibrium concentrations of tetrachloronaphthalenes (TeCNs), calculated by an ab initio method, cannot explain the field isomer patterns. Formation pathways involving chlorophenol precursor condensation reactions should be examined to see whether these isomer patterns provide a better fit to the field PCDD data. The PCB isomer patterns were fit reasonably well, but this finding could merely be an artifact of the limited data and the large number of isomers. The prediction equations of PCDFs, revised from prior work to include a symmetry number for each isomer, represented the field data patterns for the higher chlorinated isomers very well. Successful prediction of isomer patterns for partial homologue ranges suggests that these patterns are determined by a mechanism governed by Cl-position-specific preferences.