Thermal decomposition of zinc carbonate hydroxide

This study is devoted to the thermal decomposition of two zinc carbonate hydroxide samples up to 400 °C. Thermogravimetric analysis (TGA), boat experiments and differential scanning calorimetry (DSC) measurements were used to follow the decomposition reactions. The initial samples and the solid decomposition products were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and laser particle size analyzer. Results showed that zinc carbonate hydroxide decomposition started at about 150 °C and the rate of decomposition became significant at temperatures higher than 200 °C. The apparent activation energies (E_a) in the temperature range 150–240 °C for these two samples were 132 and 153 kJ/mol. The XRD analyses of the intermediately decomposed samples and the DSC results up to 400 °C suggested a single-step decomposition of zinc carbonate hydroxide to zinc oxide with not much change in their overall morphologies.     

Kinetics of thermal decomposition of nickel oxalate dihydrate in air

Thermal decomposition taking place in solid state complex, NiC₂O₄·2H₂O, has been investigated in air by means of TG–DTG/DTA, DSC, XRD. TG–DTG/DTA curves showed that the decomposition proceeds through two well-defined steps with DTA peaks closely corresponding to the weight loss obtained. XRD showed that the final decomposition product of NiC₂O₄·2H₂O was NiO. Kinetics analysis of NiC₂O₄·2H₂O decomposition steps was performed under non-isothermal conditions. The activation energies were calculated through Friedman and Flynn–Wall–Ozawa (FWO) methods, and the most possible kinetic model function has been estimated through the multiple-linear regression method. The activation energies for the two decomposition steps of NiC₂O₄·2H₂O were 171.1 ± 4.2 and 174.4 ± 8.1 kJ/mol, respectively.     

Temperature dependence of the rate constant for reactions of hydrated electrons with H, OH and H2O2

The temperature dependence of the rate constants, for the reactions of hydrated electrons with H atoms, OH radicals and H₂O₂ has been determined. The reaction with H atoms, studied in the temperature range 20–250°C gives k(20°C) = 2.4 × 10¹⁰M^-1s¹ and the activation energy E_A = 14.0 kJ mol^-1 (3.3 kcal mol^-1). For reaction with OH radicals the corresponding values are, k(20°C) = 3.1 × 10¹⁰M^-1s^-1 and E_A = 14.7 kJ mol^-1 (3.5 kcal mol^-1) determined in the temperature range 5–175°C. For reaction with H₂O₂ the values are, k(20°C) = 1.2 × 10¹⁰M^-1s^-1 and E_A = 15.6 kJ mol^-1 (3.7 kcal mol^-1) measured from 5–150°C. Thus, the activation energy for all three fast reactions is close to that expected for diffusion controlled reactions. As phosphates were used as buffer system, the rate constant and activation energy for the reaction of hydrated electron with H₂PO₄^- was determined to k(20°C) = 1.5 × 10⁷M^-1s^-1 and E_A = 7.4 kJ mol^-1 (1.8 kcal mol^-1) in the temperature range 20–200°C.     

Thermal decomposition study of the coordination compound [Fe(urea)6](NO3)3

The thermochemical behavior of the coordination compound [Fe(urea)₆](NO₃)₃ was studied by simultaneous CG–TG–DTG–DTA and mass spectrometry methods non-isothermal conditions. The compound decomposes at 200 °C into a mixture of spinel-type oxides and hematite. The nature and particle size of the final decomposition products are strongly associated with the conditions during the thermal treatments, in particular the heating rate and the calcination temperature. A certain fraction of the products are formed as nanometric particles; they show superparamagnetic behavior at room temperature. The comparably low temperature of the calcination treatments of this compound is a promising perspective to attain small sized magnetic powders.     

The effect of humidity on thermal process of zinc acetate

The thermal decomposition of zinc acetate dihydrate Zn(CH₃CO₂)₂·2H₂O in some humidity-controlled atmospheres has been successfully investigated by novel thermal analyses, which are sample-controlled thermogravimetry (SCTG), thermogravimety combined with evolved gas analysis using mass spectrometry (TG–MS) and simultaneous measurement of differential scanning calorimetry and X-ray diffractometry (XRD–DSC). The thermal processes of anhydrous zinc acetate in dry gas atmosphere by conventional linear heating experiment initiated with the sublimation around 180 °C, followed by the fusion and the decomposition over 250 °C. SCTG was useful to interpret clearly the successive reaction because the high-temperature parallel decompositions were effectively inhibited. The thermal behavior changed dramatically by introducing water vapor in the atmosphere and the thermal process was quite different from that in dry gas atmosphere. Zinc oxide (ZnO) was formed only in a humidity-controlled atmosphere, and could be easily synthesized at temperatures below 300 °C. XRD–DSC equipped with a humidity generator revealed directly the crystalline change from Zn(CH₃CO₂)₂ to ZnO. A detailed thermal process of Zn(CH₃CO₂)₂·2H₂O and the effect of water vapor are discussed.     

Thermal behavior of nitrided TiO2/In2O3 by TG–DSC–MS combined with PulseTA

TiO₂/InN (In/(Ti + In) = 6.5:100 mol) was prepared by nitridation of TiO₂/In₂O₃ by NH₃ at 580 °C for 8 h. Only the anatase TiO₂ phase was detected in the XRD measurements. The highly dispersed InN clusters on the surface of anatase TiO₂ nanocrystals were beyond the detection limit of XRD. In order to confirm the existence of InN in the products of nitridation, thermogravimetry–differential scanning calorimetry–mass spectrometry (TG–DSC–MS) coupling techniques were used for a simultaneous characterizing study of the changes of mass, enthalpy and determination of the evolved gases during the thermal decomposition of the InN and the nitrided TiO₂/In₂O₃ samples. Moreover, pulse thermal analysis (PulseTA) was combined with TG–DSC–MS for the quantitative calibration of the evolved nitrogen formed during the thermal decomposition of the InN and the nitrided TiO₂/In₂O₃. The applied technique enabled identification and quantification of the InN in the products of the nitridation of TiO₂/In₂O_3.     

Thermal solid–solid interactions and physicochemical properties of NiO/Fe2O3 system doped with K2O

The effects of calcination temperature and doping with K₂O on solid–solid interactions and physicochemical properties of NiO/Fe₂O₃ system were investigated using TG, DTA and XRD techniques. The amounts of potassium, expressed as mol% K₂O were 0.62, 1.23, 2.44 and 4.26. The pure and variously doped mixed solids were thermally treated at 300, 500, 750, 900 and 1000 °C. The catalytic activity was determined for each solid in H₂O₂ decomposition reaction at 30–50 °C. The results obtained showed that the doping process much affected the degree of crystallinity of both NiO and Fe₂O₃ phases detected for all solids calcined at 300 and 500 °C. Fe₂O₃ interacted readily with NiO at temperature starting from 700 °C producing crystalline NiFe₂O₄ phase. The degree of reaction propagation increased with increasing calcination temperature. The completion of this reaction required a prolonged heating at temperature >900 °C. K₂O-doping stimulates the ferrite formation to an extent proportional to its amount added. The stimulation effect of potassium was evidenced by following up the change in the peak height of certain diffraction lines characteristic NiO, Fe₂O₃, NiFe₂O₄ phases located at “d” spacing 2.08, 2.69 and 2.95 Å, respectively. The change of peak height of the diffraction lines at 2.95 Å as a function of firing temperature of pure and doped mixed solids enabled the calculation of the activation energy (ΔE) of the ferrite formation. The computed ΔE values were 120, 80, 49, 36 and 25 kJ mol⁻¹ for pure and variously doped solids, respectively. The decrease in ΔE value of NiFe₂O₄ formation as a function of dopant added was not only attributed to an effective increase in the mobility of reacting cations but also to the formation of potassium ferrite. The calcination temperature and doping with K₂O much affected the catalytic activity of the system under investigation.     

Synthesis and characterization of oxazolone complexes with Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) in different counterions

Oxazolone forms (1:1) complexes with Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺ chlorides, as well as forms (1:1) complexes with Co²⁺ and Cu²⁺ acetates. All the complexes are found to be non-electrolytes in DMF; tetrahedral, square-planar and octahedral structures are assigned to them based on electronic and magnetic data. IR studies reveal that the complexes are formed by donating the lone-pair electron from O and N atoms to the metal ion. The thermal decomposition of the [ML·mX·nH₂O]_y·H₂O chelates was studied by TG–DTA techniques. The mechanism of the decomposition has been established from TG–DTA data. The kinetic parameters, activation energy (E_a) and pre-exponential factor (A), were calculated from TG curves using Coats and Redfern method. Relative thermal stabilities of the chelates have been evaluated on the basis of these parameters.     

TEMPO-initiated oxidation of 2-aminophenol to 2-aminophenoxazin-3-one

The oxidation reaction of 2-aminophenol (OAP) to 2-aminophenoxazin-3-one (APX) initiated by 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) has been investigated in methanol at ambient temperature. The oxidation of OAP was followed by electronic spectroscopy and the rate constants were determined according to the rate law −d[OAP]/dt=k_obs[OAP][TEMPO]. The rate constant, activation enthalpy and entropy at 298 K are as follows: k_obs (dm³ mol⁻¹ s⁻¹)=(1.49±0.02)×10⁻⁴, E_a=18±5 kJ mol⁻¹, ΔH^‡=15±4 kJ mol⁻¹, ΔS^‡=−82±17 J mol⁻¹ K⁻¹. The results of oxidation of OAP show that the formation of 2-aminophenoxyl radical is the key step in the activation process of the substrate.     

Thermal study of palladium complexes with trans-1,2-diaminecy clohexanetetraacetic acid

Thermal decomposition processes for cyclohexanediaminetetraacetic acid (CDTA-H₄) complexes of palladium, [Pd(CDTA-H₂)] and [Pd(CDTA-H₄)Cl₂]·2 HCl·2 H₂O have been studied using TG—DTA techniques. Infrared spectroscopy and X-ray diffraction have been also used for the characterization of intermediate and final products. In the decomposition of the dichloro complex, chloride ions are released simultaneously to a ring closure reaction in which CDTA becomes tetradentate. For both compounds, the final product in the decomposition is PdO, as confirmed by the X-ray difraction pattern of a sample heated at 600°C.     

Sintering behavior and apatite formation of diopside prepared by coprecipitation process

Sintering behavior and bioactivity of diopside, CaMgSi₂O₆, prepared by a coprecipitation process were examined for its biomedical applicability. As-prepared powder was synthesized by adding aqueous ammonia to an ethanol solution containing Ca(NO₃)₂·4H₂O, Mg(NO₃)₂·6H₂O, and Si(OC₂H₅)₄ and characterized by means of TG–DTA, XRD, and TG–MS. The dried powder was X-ray amorphous and crystallized into diopside at 845.5 °C. The glass network formation by SiO₄ tetrahedra was almost completed below 800 °C. The bioactivity of the diopside prepared by sintering the compressed powder at 1100 °C for 2 h was evaluated by immersion of the sintered body in a simulated body fluid (SBF) at 36.5 °C. Leaf-like apatite particles were found to be formed on the surface of the sintered body and grew with passage of soaking time. This apatite-forming behavior in the SBF is related to the dissolution of Ca(II) ions from the sintered body in the early stage of immersion. Thus, diopside prepared by the coprecipitation process using the metal alkoxide and the metal salts was found to have an apatite-forming ability.     

Preparation and characterization of sulfated zirconia (SO4/ZrO2)/Nafion composite membranes for PEMFC operation at high temperature/low humidity

Fine particle superacidic sulfated zirconia (SO₄²⁻/ZrO₂, S-ZrO₂) was synthesized by ameliorated method, and composite membranes with different S-ZrO₂ contents were prepared by a recasting procedure from a suspension of S-ZrO₂ powder and Nafion solution. The physico-chemical properties of the membranes were studied by ion exchange capacity (IEC) and liquid water uptake measurements, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis, thermogravimetry–mass spectrometry (TG–MS) and Fourier transform infrared (FT-IR) spectroscopy. The results showed that the IEC of composite membrane increased with the content of S-ZrO₂, S-ZrO₂ was compatible with the Nafion matrix, the incorporation of the S-ZrO₂ could increase the crystallinity and also improve the initial degradation temperature of the composite membrane. The performance of single cell was the best when the S-ZrO₂ content was 15 wt.%, and achieved 1.35 W/cm² at 80 °C and 0.99 W/cm² at 120 °C based on H₂/O₂ and at a pressure of 2 atm, the performance of the single cell with optimized S-ZrO₂ was far more than that of the Nafion at the same condition (e.g. 1.28 W/cm² at 80 °C, 0.75 W/cm² at 120 °C). The 15 wt.% S-ZrO₂/Nafion composite membrane showed lower fuel cell internal resistance than Nafion membranes at high temperature and low relative humidity (RH).     

Thermal decomposition of poly(1,4-dioxan-2-one)

To evaluate the feasibility of poly(1,4-dioxan-2-one) (PPDO) as a feed stock recycling material, the pyrolysis kinetics of PPDO were investigated. The pyrolysis of PPDO exclusively resulted in the distillation of 1,4-dioxan-2-one (PDO). From thermogravimetric measurements conducted at different heating rates, the kinetic parameters of the pyrolysis: activation energy, E_a=127 kJ mol⁻¹; order of reaction, n=0; and pre-exponential factor, A=2.3×10⁹ s⁻¹, were estimated by plural analytical methods. The estimates show that the decomposition of PPDO proceeds by unzipping depolymerization as main reaction and random degradation process with lower E_a and A values. Equivalent isothermal degradation curves calculated from the thermogravimetric curves were supported by experimental isothermal degradation data. The calculation that PPDO is converted smoothly into PDO at 270°C agrees with the reported ceiling temperature of PPDO.     

Dynamic thermogravimetric degradation of gamma radiolytically synthesized Ag–PVA nanocomposites

The degradation kinetics of gamma radiolytically synthesized Ag–PVA nanocomposites was investigated by thermogravimetric method under dynamic conditions (30–600 °C) in an inert atmosphere. Thermogravimetric analysis showed that thermal degradation of composites was a two-stage process for the lower amount of nanofiller and single-stage for the higher amount of nanofiller. The Vyazovkin model-free kinetics method was applied to calculate the activation energy (E_a) of the degradation process as a function of conversion and temperature. At a given degradation temperature, PVA as a host in nanocomposite presents lower reaction velocity, while its E_a is higher than that of pure PVA.     

Solid–solid interactions between ferric and cobalt oxides as influenced by Al2O3-doping

The solid–solid interactions between pure and alumina-doped cobalt and ferric oxides have been investigated using DTA, IR and XRD techniques. Equimolar proportions of basic cobalt carbonate and ferric oxide and different amounts of aluminum nitrate were added as dopant substrate. The amounts of dopant were 0.75, 1.5, 3.0 and 4.5 mol% Al₂O₃.

The results obtained revealed that solid–solid interaction between Fe₂O₃ and Co₃O₄ takes place at temperatures starting from 700°C to produce cobalt ferrite. The degree of propagation of this reaction increases progressively as a function of precalcination temperature and Al₂O₃-doping of the reacting solids. However, the heating of pure mixed solids at 1000°C for 6 h. was not sufficient to effect the complete conversion of the reacting solids into CoFe₂O₄, while the addition of a small amount of Al₂O₃ (1.5 mol%) to ferric/cobalt mixed solids followed by precalcination at 1000°C for 6 h conducted the complete conversion of the reacting solids into cobalt ferrite. The heat treatment of pure and the 0.75 mol%-doped solids at 900 and 1000°C effected the disappearance of most of IR transmission bands of the free oxides with subsequent appearance of new bands characteristic for the CoFe₂O₄ structure. An increase in the amount of Al₂O₃ added from 1.5–4.5 mol% to the mixed solids precalcined at 1000°C led to the disappearance of all bands of free oxides and appearance of all bands of cobalt ferrite. The promotion effect of Al₂O₃ in cobalt ferrite formation was attributed to an effective increase in the mobility of the various reacting cations. The activation energy of formation (ΔE) of CoFe₂O₄ phase was determined for pure and doped solids. The computed values of ΔE were, respectively, 99.6, 87.8, 71.9, 64.7 and 48.7 kJ mol⁻¹ for the pure solid and those treated with 0.75, 1.5, 3 and 4.5 mol% Al₂O₃.     

A study of the sensitivity and decomposition of 1,3,5-trinitro-2-oxo-1,3,5-triazacyclo-hexane

The thermal decomposition and thermal stability of 1,3,5-trinitro-2-oxo-1,3,5-triazacyclohexane (keto-RDX or K-6) was studied. The keto-RDX synthesis is described, mass spectra (electron impact (70 eV) and chemical ionization) similar to RDX spectra registered under identical conditions are presented, and mass spectroscopy fragmentation paths are proposed. The LI-MS (laser induced/mass spectroscopic) results imply that the first step in the decomposition of keto-RDX is the elimination of NO₂ or HONO and subsequent breakdown of the triazacyclohexane ring. The thermal stability, activation energy (E_a = 140 kJ mol⁻¹), and frequency factor (K₀ = 9 × 10⁹ s⁻¹) in the temperature interval 90-120°C were measured using chemiluminescence (NO detection only). The activation energy was also determined from DSC data using the ASTM method E 698-79, and was found to be 280 kJ mol⁻¹ with a frequency factor of 7.0 × 10²⁹ s⁻¹ in the temperature interval 175-200°C. Microcalorimetry, drop-weight test, friction test, and ignition temperature (Wood's metal bath) measurements were also conducted. Quantum mechanical calculations (semi-empirical method with PM3 set at the unrestricted Hartree-Fock level) were conducted to correlate the sensitivity and thermal decomposition with those of RDX. No significant differences in bond-breaking energies for RDX and keto-RDX were found. Conclusions drawn from the experiments are that the decomposition of keto-RDX is auto-catalytic, and that the sensitivity of keto-RDX is not connected with the initial bond-breaking step. More than one method for measuring the risk involved in handling an explosive is necessary since the sensitivity depends on different stages in the decomposition.     

Gelation of β-lactoglobulin in the presence of propylene glycol alginate: kinetics and gel properties

The role of the non-gelling polysaccharide, propyleneglycol alginate (PGA), on the dynamics of gelation and gel properties of β-lactoglobulin (β-lg) under conditions where the protein alone does not gel (6%) was analyzed. To this end, the kinetics of gelation, aggregation and denaturation of β-lg in the mixed systems (pH 7) were studied at different temperatures (64–88 °C). The presence of PGA increased thermal stability of β-lg. The rate of β-lg denaturation was decreased and the onset and peak denaturation temperatures increased by 2.2–2.4 °C. PGA promoted the formation of larger aggregates that continued to grow in time. An average aggregate diameter of approximately 300 nm is reached at the gel point in the mixed β-lg+PGA systems, irrespective of the heating temperature. Comparing the activation energies for the aggregation (193 kJ/mol), denaturation (422 kJ/mol) and formation of the primary gel structure (1/t_gel) (256 kJ/mol) processes in the mixed protein–polysaccharide system, it can be concluded that the rate determining step in the formation of the primary gel structure would be the aggregation of protein. E_a values for the processes after the gel point (solid phase gelation) suggest a diffusion limited process because of the high viscosity of the solid gelling matrix. The characteristics of the mixed β-lg+PGA gels in terms of rheological and textural parameters, water loss and microstructure were studied as a function of heating temperature and time. The extent of aggregation and the type of interactions involved, prior to denaturation seem to be very important in determining the gel structure and its properties.     

Structure and conformational properties of carbonylbisimidosulfuryl fluoride, O=C(N=S(O)F2)2

The molecular structure and conformational properties of O=C(N=S(O)F₂)₂ (carbonylbisimidosulfuryl fluoride) were determined by gas electron diffraction (GED) and quantumchemical calculations (HF/3-21G* and B3LYP/6-31G*). The analysis of the GED intensities resulted in a mixture of 76(12)% syn–syn and 24(12)% syn–anti conformer (ΔH⁰=H⁰(syn–anti)−H⁰(syn–syn)=1.11(32) kcal mol⁻¹) which is in agreement with the interpretation of the IR spectra (68(5)% syn–syn and 32(5)% syn–anti, ΔH⁰=0.87(11) kcal mol⁻¹). syn and anti describe the orientation of the S=N bonds relative to the C=O bond. In both conformers the S=O bonds of the two N=S(O)F₂ groups are trans to the C–N bonds. According to the theoretical calculations, structures with cis orientation of an S=O bond with respect to a C–N bond do not correspond to minima on the energy hyperface. The HF/3-21G* approximation predicts preference of the syn–anti structure (ΔE=−0.11 kcal mol⁻¹) and the B3LYP/6-31G* method results in an energy difference (ΔE=1.85 kcal mol⁻¹) which is slightly larger than the experimental values. The following geometric parameters for the O=C(N=S)₂ skeleton were derived (r_a values with 3σ uncertainties): C=O 1.193 (9) Å, C–N 1.365 (9) Å, S=N 1.466 (5) Å, O=C–N 125.1 (6)° and C–N=S 125.3 (10)°. The geometric parameters are reproduced satisfactorily by the HF/3-21G* approximation, except for the C–N=S angle which is too large by ca. 6°. The B3LYP method predicts all bonds to be too long by 0.02–0.05 Å and the C–N=S angle to be too small by ca. 4°.     

Synthesis, characterization and thermal investigation of M[M(C2O4)3]·xH2O (x=4 for M=Cr(III); x=2 for M=Sb(III) and x=9 for M=La(III))

The complexes, M[M(C₂O₄)₃]·xH₂ O, where x=4 for M=Cr(III), x=2 for M=Sb(III) and x=9 for M=La(III) have been synthesized and their thermal stability was investigated. The complexes were characterized by elemental analysis, IR and electronic spectral data, conductivity measurement and powder X-ray diffraction (XRD) studies. The chromium(III)tris(oxalato)chromate(III)tetrahydrate (COT), Cr[Cr(C₂ O₄)₃]·4H₂O, released water in a stepwise fashion. Removal of the last trace of water was accompanied by a partial decomposition of the oxalate group. Thermal investigation using TG, DTG and DTA techniques in air produced Cr₂O₃ at 858°C through the intermediate formation of Cr₂O₃ and CrC₂O₄ at around 460°C. While DSC study in nitrogen up to 670°C produced a mixture of Cr₂O₃ and CrC₂O₄. In antimony(III)tris(oxalato)antimonate(III)dihydrate (AOD), Sb[Sb(C₂O₄)₃]·3H₂O the dehydration took place during the decomposition of precursor at 170–290°C and finally at ca. 610°C Sb₂ O₅ along with trace amounts of Sb₂O₄ were produced. Trace amount of Sb₂O₃ and Sb along with Sb₂O is proposed as the end product at 670°C of AOD in nitrogen. The oxide La₂O₃ is formed at 838°C from the study with TG, DTG and DTA in air of lanthanum(III)tris(oxalato)lanthanum(III)nonahydrate (LON), La[La(C₂O₄)₃]·9H₂O. Intermediate dioxycarbonate, La₂O₂CO₃ was generated at 526°C prior to its decomposition to lanthanum oxide in air; whereas in N₂ the formation of La₂(CO₃)₃ at 651°C was proposed. The thermal parameters have been evaluated for each step of the dehydration and decomposition of COT, AOD and LON using five non-mechanistic equations i.e. Flynn and Wall, Freeman and Carroll, Modified Freeman and Carroll, Coats–Redfern and MacCallum–Tanner equations. Kinetic parameters, such as, E^*, k_o, ΔH^*, ΔS^* etc. were also supplemented by DSC studies in nitrogen for all the three complexes. Some of the intermediate species have been identified by analytical and powder XRD studies. Tentative schemes has been proposed for the decomposition of all three compounds in air and nitrogen.     

Gaseous nitryl azide N4O2: A joint theoretical and experimental study

Gaseous nitryl azide N₄O₂ is generated by the heterogeneous reaction of gaseous ClNO₂ with freshly prepared AgN₃ at −50 °C. The geometric and electronic structure of the molecule in the gas phase has been characterized by in situ photoelectron spectroscopy (PES) and quantum chemical calculations. The experimental first vertical ionization energy of N₄O₂ is 11.39 eV, corresponding to the ionization of an electron on the highest occupied molecular orbital (HOMO) {4a″(π_{nb(N4–N5–N6)})}⁻¹. An apparent vibrational spacing of 1600 ± 60 cm⁻¹ (ν_asO1N2O3) on the second band at 12.52 eV (π_{nb(O1–N2–O3)}) further confirms the preference of energetically stable chain structure in the gas phase. To complement the experimental results, the potential-energy surface of this structurally novel transient molecule is discussed. Both calculations and spectroscopic results suggest that the molecule adopts a trans-planar chain structure, and a five-membered ring decomposition pathway is more favorable.