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1.
Gaussian-2 ab initio calculations were performed to examine the six modes of unimolecular dissociation of cis-CH3CHSH+ (1+), trans-CH3CHSH+ (2+), and CH3SCH2+ (3+): 1+→CH3++trans-HCSH (1); 1+→CH3+trans-HCSH+ (2); 1+→CH4+HCS+ (3); 1+→H2+c-CH2CHS+ (4); 2+→H2+CH3CS+ (5); and 3+→H2+c-CH2CHS+ (6). Reactions (1) and (2) have endothermicities of 584 and 496 kJ mol−1, respectively. Loss of CH4 from 1+ (reaction (3)) proceeds through proton transfer from the S atom to the methyl group, followed by cleavage of the C–C bond. The reaction pathway has an energy barrier of 292 kJ mol−1 and a transition state with a wide spectrum of nonclassical structures. Reaction (4) has a critical energy of 296 kJ mol−1 and it also proceeds through the same proton transfer step as reaction (3), followed by elimination of H2. Formation of CH3CS+ from 2+ (reaction (5)) by loss of H2 proceeds through protonation of the methine (CH) group, followed by dissociation of the H2 moiety. Its energy barrier is 276 kJ mol−1. On both the MP2/6-31G* and QCISD/6-31G* potential-energy surfaces, the H2 1,1-elimination from 3+ (reaction (6)) proceeds via a nonclassical intermediate resembling c-CH3SCH2+ and has a critical energy of 269 kJ mol−1.  相似文献   

2.
The state-selective energy transfer from two-photon excited Xe(6p) to H2O and the subsequent reaction has been studied by measured of emission spectra of OH (A 2Σ+ → X 2Π). The vibrational population ratios, Nv=1/Nv=0, are 0.52 ± 0.01 in a free jet and 0.37 ± 0.02 in a bulb. This reveals the difference in dissociation dynamics following the intra-complex and the intermolecular electronic energy transfers from Xe(6p) to H2O.  相似文献   

3.
A mixture of NF3 and Ar is passed through an rf discharge in a flow-system to produce, among other species, F and NF2. When H2, D2, or CH4 are added downstream, reactions with F atoms produce vibrationally excited HF or DF together with H, D, or CH3. The latter free radicals can react with NF2, probably by an elimination reaction to produce electronically excited NF: NF2(2B1) + H(D, CH3) → HF*(DF* + NF(a1Δ). A vibrational-to-electronic energy transfer process between the products of this reaction then produces the next higher state of NF: HF(ν 2) + NF(a1Δ) → HF(ν−2) + NF(b1Σ+). A similar transfer process has also been found between the electronically excited a1Δ states of O2 and NF: O2(a1Δ) + NF(a1Δ) → O2(X3Σ) + NF(b1Σ+). The H or D atoms but not the CH3 radicals are then found to react with either NF(a1Δ) or NF(X3Σ) to produce electronically excited N(2D) atoms, which in turn react with the NF(a1Δ) molecules to produce N2(B3Πg). The observed nitrogen first positive radiation has been demonstrated to be produced entirely by this reaction mechanism rather than by the N(4S) recombination that accounts for the Rayleigh afterglow. In addition, the occurrence of the reaction N(2D) + N2O → NO(B2Πr) + N2 (X1Σ+g) has been verified. Finally we have observed emission at 3344 Å, which we attribute to the NF(A3Π), which has not been previously reported.  相似文献   

4.
Mg+—Ar ion—molecule complexes are produced in a pulsed supersonic nozzle cluster source. The complexes are mass selected and studied with laser photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer system. An electronic transition assigned as X 2Σ+2Π is observed with an origin at 31387 cm−1 (vac) for 24Mg+—Ar. The 24Mg+—Ar spectrum is characterized by a 15 member progression with a frequency (ω′e) of 272 cm−1. An extrapolation of this progression fixes the excited state dissociation energy (Do) at 5552 cm−1. The corresponding ground-state value (Do) is 1270 cm−1 (3.6 kcal/mol). The 2Π , spin—orbit splitting is 76 cm.  相似文献   

5.
The mechanism of the H2NO(2B1)→NO(2Π)+H2 reaction has been examined using ab initio molecular orbital methods. Ground-state and first-excited-state potential surfaces were plotted at the FOCI/cc-pVTZ level of theory as functions of two appropriate internal degrees of freedom. A conical intersection was found on the Cs pathway that is symmetric with respect to the plane perpendicular to the molecular plane of C2v H2NO(2B1). It is therefore considered that trajectories that start from H2NO(2B1) towards the product region detour around the conical intersection, pass through the neighborhood of the transition state that is located at the saddle point on the Cs pathway, and finally reach the products, NO(2Π)+H2. Thus we can explain the mechanism of the H2NO(2B1)→NO(2Π)+H2 reaction, which has remained unclear to date.  相似文献   

6.
Saddle point geometries and barrier heights have been calculated for the H abstraction reaction HO2(2A″)+H(2S) → H2(1Σ+g)+O2(3Σg) and the concerted H approach-O removing reaction HO2 (2A″)+H(2S) → H2O(1A1)+O(3P) by using SDCI wavefunctions with a valence double-zeta plus polarization basis set. The saddle points are found to be of Cs symmetry and the barrier heights are respectively 5.3 and 19.8 kcal by including size consistent correction. Moreoever kinetic parameters have been evaluated within the framework of the TST theory. So activation energies and the rate constants are estimated to be respectively 2.3 kcal and 0.4×109 ℓ mol−1 s−1 for the first reaction, 20.0 kcal and 5.4.10−5 ℓ mol−1 s−1 for the second. Comparison of these results with experimental determinations shows that hydrogen abstraction on HO2 is an efficient mechanism for the formation of H2 + O2, while the concerted mechanism envisaged for the formation of H2O + O is highly unlikely.  相似文献   

7.
The orbiting resonance theory of hydrogen-atom recombination predicts a non-statistical ortho-to-para ratio for the molecular hydrogen formed via this mechanism. It is shown that the predicted (o/p) ratio changes very drastically due to a recent increase of only 4 cm−1 in the experimental ground-state dissociation energy of H2(X1Σg+).  相似文献   

8.
The continuous absorption spectrum of molecular bromine has been examined using laser induced photodissociation spectroscopy. In this technique, Br2 molecules are photolyzed using a flashlamp-pumped dye laser; the atomic products of the dissociation are then monitored by time-resolved resonance absorption spectroscopy in the vacuum ultraviolet. The relative absorptivities for the transitions B3Πo+u ← X1Σ+g and 1Π1u ← X1Σ+g have been obtained at 18350, 21010 and 22125 cm−1.  相似文献   

9.
Measurements of electron stimulated desorption (ESD) yields of O, at incident electron energies below 20 eV, from 0.15 monolayers (ML) of O2 physisorbed at 20 K on a variety of molecular solids have been performed. It is observed that for O2 condensed on 4 ML of H2O, the O signal from dissociative electron attachment (DEA) to O2 is entirely absent. We attribute this to a complete quenching of the dissociative 2Πu, 2Σ+g, and 2Σ+u, resonances of O2 by the adjacent water molecules.  相似文献   

10.
The recombination of nitrogen atoms on polycrystalline samples of cobalt and nickel produces metastable electronically excited nitrogen molecules, probably N2(W3Δu), which are collisionally transferred to the N2(B3Πg) state. Information about vibrational relaxation of the metastable state by N2(X1Σ+g) is inferred from composition dependent changes in the observed first positive emission spectrum [N29A3Σ+g)−N2(B3Πg] with the aid of multilevel, steady-state, kinetic model.  相似文献   

11.
The reaction of linear form carbon cluster C3 molecules in their 1Σ ground state with NO (X2Π) radicals is explored theoretically to investigate the formation of hitherto undetected NCCCO molecules in the interstellar medium via a neutral-neutral reaction. The doublet potential energy surface is worked out by the ab initio MO calculations at the CCSD(T)/cc-pVTZ//B3LYP/6-311G(d,p)+ZPE level of theory. It is shown that the main pathway of the C3(1Σ)+NO(X2Π) reaction involves the N-atom of NO attacking the side C-atom of the 1C3 molecule first to form the adduct CCCNO, followed by the N-shift to give I6 CCNCO, and then to the main products P1 (CCN+CO). Alternatively, I6 can be converted via the N-shift again to I9 (CN)CCO, and then it leads to the minor products P2 (CNC+CO) and P3 NCCCO. Since the three pathways have zero threshold energy and proceed via strongly bound energized complexes, they should possess the character of negative temperature dependence, and might be quite rapid even at very low temperature. The reaction represents facile neutral-neutral pathways to produce hitherto undetected CCN, CNC and NCCCO molecules in interstellar environments.  相似文献   

12.
Large-basis-set calculations of near Hartree-Fock accuracy were performed on CO+(1σ-hole 2Σ+) and CO+)2σ-hole, 2Σ+); correlation energies for these systems and for CO were calculated using an atoms-in-molecule approach, relativistic energies and vibrational structure corrections were also considered. The results are: IP(CO, 1σ) = 542.4 (542.57) eV, IP(CO,2σ) = 297.0 (296.24) cV, Dc(CO, 1Σ+) = 10.8 (11.1) Ev, D3(CO+, 1σ, 2Σ+) = 11.9 eV, De(CO+, 2σ, 2Σ+) = 9.1 eV, where IP and De stand respectively for ionization potential and dissociation energy, and where the numbers in parentheses refer to the most recent experimental values. The electron transfers resulting from the ionization of inner-shell electrons are discussed. Finally a quantitative correlation is developed correlating absolute chemical shifts to charge densities. Agreement between the calculated values and those derived from the correlation is quite satisfactory.  相似文献   

13.
Autoionizing Rydberg levels of Li2 molecules in a supersonic molecular beam are populated by stepwise excitation with two tunable pulsed dye lasers. The observed autoionization spectra show severe perturbations. Based on calculations of quantum defects and a perturbation treatment of l-uncoupling a tentative assignment of Rydberg series up to n = 32 is proposed. The convergence limits of these series yield a value of IP = 41475 cm−1 for the adiabatic ionization potential and a vibrational constant ωe = 263 cm−1 for the X2Σ+g ground state of Li+2. The experimental results are compared with ab initio calculations combined with a core polarization potential, which yield the potential curve. the dissociation energy, the quadrupole moment and the vibrational frequency for the X2Σ+g ground state of Li+2, in the excellent agreement with experimental findings.  相似文献   

14.
Three-dimensional trajectory surface hopping calculations were performed on two diabatic energy surfaces. The covalent surface describes the K(2S) + O2(3Σg) state and the ionic surface K+(1S) + O2(2Πg). Transitions from one surface to another were computed through the Landau—Zener model. At small deflection angles, the energy loss distribution exhibits two peaks, as observed, due to O2 in its electronic ground state and to vibrationally excited O2.  相似文献   

15.
Quasiclassical trajectory calculations have been performed to determine the effect of reactant collision energy on product state distributions in the reaction O(1D) + H2 → OH(2Π) + H. The product vibrational distribution becomes more excited as the collision energy is increased. This is not due to an increase in the cross section for collinear abstraction. A detailed analysis has shown that strong O---H2 repulsion, which occurs during the insertion of the O into the H---H bond, converts the kinetic energy of the reacting system to vibrational motion of the intermediate.  相似文献   

16.
Predissociation of the A 2Σ+ state is treated by an exact theory employing two frame transformation matrices, each of which connects the atomic term limits (O(3P) and O(1D)) to the correlating adiabatic Born—Oppenheimer states. Resonances corresponding to the higher (v 7) rovibrational levels of the A 2Σ+ state are predicted to have asymmetric (Fano-type) profiles. The branching ratios of O(3Pj, J = 0, 1, 2) are shown to be influenced by nonadiabatic interactions in the Franck—Condon region between the A 2Σ+ and dissociative 4Σ, 2Σ and 4Π states. The branching ratios show a strong variation along asymmetric resonances, while remaining energy independent along Lorentzian resonances.  相似文献   

17.
The Ca(1D2, 3PJ) + CH3 → CaI(A,B) + CH3 reactions system has been studied by measuring its chemiluminescence under beam-gas conditions. Absolute values of the state-to-state reaction cross-sections were determined at low collision energy . In addition, the electronic branching ratio and product energy disposal have been determined for each metastable reaction. The major changed observed in the chemiluminescence when comparing the Ca(1D2) reaction versus that of Ca(3PJ) is the total yield associated with the former reaction. To the best of our spectral resolution neither the electronic branching ratio e.g. CaI(A)/CaI(B) nor the internal CaI energy disposal change significantly as the metastable Ca(1D2)/Ca(3PJ) ratio is varied. In spite of the fact that the Ca(3PJ) reaction is less exoergic, the CaI product appears with a higher fraction of internal energy than that of Ca(1D2) reaction. Thus, the fraction of the total energy appearing in CaI internal energy amounts to 57.5% in the Ca(3PJ) reaction while it is 19.3% only for the Ca(1D2) reaction. This difference is discussed in the light of a distinct mechanism associated with the attack of the excited Ca atom into the C---I bond. No significant chemiluminescence yield was found for the energetically open CaCH*3 channels.

The product chemiluminescence polarization was also measured as a function of the metastable concentration. A significant degree of polarization was found depending upon the specific electronic excitation. The analysis of the polarization emission associated to the parallel CaI(X 2Σ+ ← B 2Σ+) emission led into a strong polarization of the product rotational angular momentum. The comparison of the product rotational alignment for the kinematically identical Ca(1D2, 3PJ, 1P1) + CH3 → CaI* (B2Σ+) + CH3 reaction system showed that the CaI rotational polarization diminishes in the 3PJ1D21P1 sequence, e.g. as the reaction exothermicity increases. In addition the degree of polarization associated with other emission bands as for example CaI(X 2Σ+ ← A 2Π1/2) indicates the presence of a parallel transition which was been interpreted as mixing of Hund's case (a) and (c) appropriate for this heavy CaI diatom produced with a high rotational excitation.  相似文献   


18.
C.J. Reid 《Chemical physics》1996,210(3):501-511
Translational-energy spectroscopy was applied to collisional-excitation and charge-inversion reactions of CF+, CCl+, SiF+ and SiCl+ in order to gain energetic and bond-length information about the anionic and excited-cationic states of the title molecules. The excitation spectra revealed that the ã3Π state, known in CCl+ and SiCl+, has a term energy of 4.85 ± 0.15 eV in CF+ and 4.70 ± 0.20 eV in SiF+, while the 11Π state, known in CCl+, is not below the dissociation threshold in CF+, SiF+ and SiCl+. These data, and bond-length estimates for the ã3Π states, are consistent with documented ab initio predictions except for re of CF+3Π) which seems to be larger than 1.21 Å. Charge-inversion spectra indicated that beams of monohalide cations formed from the tetrahalides, contained substantial proportions of ã3Π-state ions, and, in the case of CCl, SiF and SiCl, the broadness of spectral peaks was taken as evidence for the stability of the ã1Δ-state anion. Adiabatic electron affinities were deduced to be 0.49 ± 0.15 eV, 0.89 ± 0.20 eV, 1.34 ± 0.30 eV and 1.40 ± 0.30 eV for the title molecules, respectively.  相似文献   

19.
Rui Yang  Yu Gong  Mingfei Zhou   《Chemical physics》2007,340(1-3):134-140
The reaction products of palladium atoms with molecular oxygen in solid argon have been investigated using matrix isolation infrared absorption spectroscopy and quantum chemical calculations. In addition to the previously reported mononuclear palladium–dioxygen complexes: Pd(η2–O2) and Pd(η2–O2)2, dinuclear palladium–dioxygen complexes: Pd22–O2) and Pd22–O2)2 were formed under visible light irradiation and were identified on the basis of isotopic substitution and theoretical calculations. In addition, experiments doped with xenon in argon coupled with theoretical calculations suggest that the Pd(η2–O2), Pd22–O2) and Pd22–O2)2 complexes are coordinated by two argon or xenon atoms in solid argon matrix, and therefore, should be regarded as the Pd(η2–O2)(Ng)2, Pd22–O2)(Ng)2 and Pd22–O2)2(Ng)2 (NgAr or Xe) complexes isolated in solid argon.  相似文献   

20.
CAS SCF and CCI calculations have been performed in order to establish the existence or non-existence of the HO3 radical. The potential surface for the dissociation reaction, HO3 → O2(3Σ) + OH, along one chosen coordinate has been calculated. The calculations show that although the wavefunctions describing the short-distance and long-distance states are of different character, the energies are the same and the curve connecting the states is very flat. There is probably no barrier towards dissociation of the radical. However, the existence of HO3 can still not be excluded.  相似文献   

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