Imaging the nature of the mode-specific chemistry in the reaction of Cl atom with antisymmetric stretch-excited CH4

Following up our preliminary communication [Kawamata et al., Phys. Chem. Chem. Phys. 10, 4378 (2008)], the effects of the antisymmetric-stretching excitation of methane on the Cl((2)P(3/2))+CH(4) reaction are examined here over a wide range of initial collision energy in a crossed molecular beam imaging experiment. The antisymmetric stretch of CH(4) is prepared in a single rovibrational state of (v(3)=1, j=2) by direct infrared absorption, and the major product states of CH(3)(v=0) are probed by a time-sliced velocity-map imaging method. We find that at fixed collision energies, the stretching excitation promotes reaction rate. Compared to the ground-state reaction, this vibrational enhancement factor is, however, no more effective than the translational enhancement. The correlated HCl(v'=1) vibrational branching fraction shows a striking dependence on collision energies, varying from 0.7 at E(c)=2 kcal mol(-1) to about 0.2 at 13 kcal mol(-1). This behavior resembles the previously studied Cl+CH(2)D(2)(v(6)=1), but is in sharp contrast to the Cl+CHD(3)(v(1)=1) and CH(2)D(2)(v(1)=1) reactions. Dependences of experimental results on the probed rotational states of CH(3)(v=0) are also elucidated. We qualitatively interpret those experimental observations based on a conceptual framework proposed recently.     

Potential energy surface, kinetics, and dynamics study of the Cl+CH4-->HCl+CH3 reaction

A modified and recalibrated potential energy surface for the gas-phase Cl+CH4-->HCl+CH3 reaction is reported and tested. It is completely symmetric with respect to the permutation of the four methane hydrogen atoms and is calibrated with respect to updated experimental and theoretical stationary point properties and experimental forward thermal rate constants. From the kinetics point of view, the forward and reverse thermal rate constants and the activation energies were calculated using the variational transition-state theory with semiclassical transmission coefficients over a wide temperature range of 150-2500 K. The theoretical results reproduce the available experimental data, with a small curvature of the Arrhenius plot which indicates the role of tunneling in this hydrogen abstraction reaction. A dynamics study was also performed on this PES using quasiclassical trajectory (QCT) calculations, including corrections to avoid zero-point energy leakage along the trajectories. First, we found a noticeable internal energy in the coproduct methyl radical, both in the ground-state [CH4 (v=0)] and vibrationally excited [CH4 (v=1)] reactions. This CH3 internal energy was directly precluded in some experiments or oversimplified in previous theoretical studies using pseudotriatomic models. Second, our QCT calculations give HCl rotational distributions slightly hotter than those in experiment, but correctly describing the experimental trend of decreasing the HCl product rotation excitation in going from HCl (v'=0) to HCl (v'=1) for the CH4 (v=1) reaction. Third, the state specific scattering distributions present a reasonable agreement with experiment, although they tend to make the reaction more forward and backward scattered than found experimentally probably because of the hotter rotational distribution and the deficiencies of the QCT methods.     

Reaction dynamics of Cl+CH3SH: rotational and vibrational distributions of HCl probed with time-resolved Fourier-transform spectroscopy

Rotationally resolved infrared emission spectra of HCl(v=1-3) in the reaction of Cl+CH3SH, initiated with radiation from a laser at 308 nm, are detected with a step-scan Fourier-transform spectrometer. Observed rotational temperature of HCl(v=1-3) decreases with duration of reaction due to collisional quenching; a short extrapolation to time zero based on data in the range 0.25-4.25 micros yields a nascent rotational temperature of 1150+/-80 K. The rotational energy averaged for HCl(v=1-3) is 8.2+/-0.9 kJ mol(-1), yielding a fraction of available energy going into rotation of HCl, fr=0.10+/-0.01, nearly identical to that of the reaction Cl+H(2)S. Observed temporal profiles of the vibrational population of HCl(v=1-3) are fitted with a kinetic model of formation and quenching of HCl(v=1-3) to yield a branching ratio (68+/-5):(25+/-4):(7+/-1) for formation of HCl(v=1):(v=2):(v=3) from the title reaction and its thermal rate coefficient k(2a)=(2.9+/-0.7)x10(-10) cm(3) molecule(-1) s(-1). Considering possible estimates of the vibrational population of HCl(v=0) based on various surprisal analyses, we report an average vibrational energy 36+/-6 kJ mol(-1) for HCl. The fraction of available energy going into vibration of HCl is f(v)=0.45+/-0.08, significantly greater than a value fv=0.33+/-0.06 determined previously for Cl+H2S. Reaction dynamics of Cl+H(2)S and Cl+CH3SH are compared; the adduct CH3S(Cl)H is likely more transitory than the adduct H(2)SCl.     

State-resolved dynamics of the CH(A2Delta) channels from single and multiple photon dissociation of bromoform in the 10-20 eV energy range

Single photon dissociation of bromoform using synchrotron radiation has been investigated by Fourier transform visible fluorescence spectroscopy (FTVIS). The photodissociation of bromoform in the 12-18 eV energy range results in several products, among which are the CH(A2Delta) and CH(B2Sigma) radicals. Vibrational and rotational state distributions of the CH(A2Delta) are determined from their fluorescence spectra. From the threshold photon energy above which emission from the CH(A2Delta) radicals is observed, the most likely process leading to CH(A) formation is CHBr3 --> CH + 3Br rather than CHBr3 --> CH + Br + Br2. The rotational Boltzmann temperatures in the CH(A --> X) emission spectra for v' = 0 and v' = 1 range between 1570 and 3650 K, depending on the excitation photon energy. From the high rotational excitation, the results suggest that the mechanism for the loss of three bromine atoms is most likely sequential. A small negative emission anisotropy of the CH(A) radicals [(Ipar - Iper)/(Ipar + 2Iper) = -0.024 +/- 0.005] is constant across the action spectrum; a small net absorption dipole of CHBr3 in the vacuum ultraviolet is parallel to the 3-fold symmetry axis of the CHBr3 molecule. The state distributions of the CH(A2Delta) radicals from multiphoton dissociation of bromoform using the 266 nm output (three photons) of a femtosecond laser (Boltzmann temperatures: T(v'=0)(rot)= 4250 +/- 300 K; T(v'=1)(rot)= 3100 +/- 550 K) are compared to those from the single photon dissociation results (Boltzmann temperatures: T(v'=0)(rot)= 3650 +/- 150 K; T(v'=1)(rot)= 2400 +/- 200 K) at the same total excitation energy under collision free conditions. The analysis of the CH(A) rotational populations shows hotter rotational populations for the femtosecond experiment, also suggesting sequential dissociation of the bromoform in the femtosecond experiment. The duration of the femtosecond laser pulse is approximately 180 fs, setting a limit on the time scales for the multiple dissociations.     

Effect of bending and torsional mode excitation on the reaction Cl+CH4-->HCl+CH3

A beam containing CH(4), Cl(2), and He is expanded into a vacuum chamber where CH(4) is prepared via infrared excitation in a combination band consisting of one quantum of excitation each in the bending and torsional modes (nu(2)+nu(4)). The reaction is initiated by fast Cl atoms generated by photolysis of Cl(2) at 355 nm, and the resulting CH(3) and HCl products are detected in a state-specific manner using resonance-enhanced multiphoton ionization (REMPI). By comparing the relative amplitudes of the action spectra of Cl+CH(4)(nu(2)+nu(4)) and Cl+CH(4)(nu(3)) reactions, we determine that the nu(2)+nu(4) mode-driven reaction is at least 15% as reactive as the nu(3) (antisymmetric stretch) mode-driven reaction. The REMPI spectrum of the CH(3) products shows no propensity toward the formation of umbrella bend mode excited methyl radical, CH(3)(nu(2)=1), which is in sharp distinction to the theoretical expectation based on adiabatic correlations between CH(4) and CH(3). The rotational distribution of HCl(v=1) products from the Cl+CH(4)(nu(2)+nu(4)) reaction is hotter than the corresponding distribution from the Cl+CH(4)(nu(3)) reaction, even though the total energies of the two reactions are the same within 4%. An explanation for this enhanced rotational excitation of the HCl product from the Cl+CH(4)(nu(2)+nu(4)) reaction is offered in terms of the projection of the bending motion of the CH(4) reagent onto the rotational motion of the HCl product. The angular distributions of the HCl(nu=0) products from the Cl+CH(4)(nu(2)+nu(4)) reaction are backward scattered, which is in qualitative agreement with theoretical calculation. Overall, nonadiabatic product vibrational correlation and mode specificity of the reaction indicate that either the bending mode or the torsional mode or both modes are strongly coupled to the reaction coordinate.     

Imaging CH3SH photodissociation at 204 nm: the SH + CH3 channel

The SH + CH(3) product channel for the photodissociation of CH(3)SH at 204 nm was investigated using the sliced velocity map ion imaging technique with the detection of CH(3) products using state selective (2+1) resonance enhanced multiphoton ionization (REMPI). Images were measured for CH(3) formed in the ground and excited vibrational states (v(2) = 0, 1, and 2) of the umbrella mode from which the correlated SH vibrational state distributions were determined. The vibrational distribution of the SH fragment in the SH + CH(3) channel at 204 nm is clearly inverted and peaks at v = 1. The highly negative anisotropy parameter of the CH(3) (v(2) = 0, 1, and 2) products is indicative of a fast dissociation process for C-S bond cleavage. Two kinds of slower CH(3) products were also observed (one of which was partly vibrationally resolved) that are assigned to a two-step photodissociation processes, in which the first step is the production of the CH(3)S (X(2)E) radical via cleavage of the S-H bond in CH(3)SH, followed by probe laser photodissociation of nascent CH(3)S radicals yielding CH(3)(X(2)A(1), v(2) = 0-2) + S((3)P(j)/(1)D) products.     

Product pair correlation in CH3OH photodissociation at 157 nm: the OH + CH3 channel

The OH + CH(3) product channel for the photodissociation of CH(3)OH at 157 nm was investigated using the velocity map imaging technique with the detection of CH(3) radical products via (2+1) resonance-enhanced multiphoton ionization (REMPI). Images were measured for the CH(3) formed in the ground and excited states (v(2) = 0, 1, 2, and 3) of the umbrella vibrational mode and correlated OH vibrational state distributions were also determined. We find that the vibrational distribution of the OH fragment in the OH + CH(3) channel is clearly inverted. Anisotropic distributions for the CH(3) (v(2) = 0, 1, 2, and 3) products were also determined, which is indicative of a fast dissociation process for the C-O bond cleavage. A slower CH(3) product channel was also observed, that is assigned to a two-step photodissociation process, in which the first step is the production of a CH(3)O(X (2)E) radical via the cleavage of the O-H bond in CH(3)OH, followed by probe laser photodissociation of the nascent CH(3)O radicals yielding CH(3)(X (2)A(1), v = 0) products.     

Steric effect in the energy transfer reaction of oriented CO (a 3Π, v'=0, Ω=1 and 2) + NO (X 2Π) → NO (A 2Σ+, B 2Π) + CO (X 1Σ+)

The oriented CO (a (3)Π, v' = 0, Ω = 1 and 2) beam has been prepared by using an electric hexapole and applied to the energy transfer reaction of CO (a (3)Π, v' = 0, Ω = 1 and 2) + NO (X (2)Π) → NO (A (2)Σ(+), B (2)Π) + CO (X (1)Σ(+)). The emission spectra of NO (A (2)Σ(+), B(2)Π) have been measured at three orientation configurations (C-end, O-end, random). The shape of the emission spectra (and/or the internal excitation of products) turns out to be insensitive to the molecular orientation. The vibrational distributions of NO (A (2)Σ(+), v' = 0-2) and NO (B (2)Π, v' = 0-2) are determined to be N(v'=0):N(v'=1):N(v'=2) = 1:0.40 ± 0.05:0.10 ± 0.05 and N(v'=0):N(v'=1):N(v'= 2) = 1:0.6 ± 0.1:0.7 ± 0.1, respectively, and the branching ratio γ/β [=NO (A (2)Σ(+))/NO (B (2)Π)] is estimated to be γ/β ～ 0.3 ± 0.1 by means of spectral simulation. These vibrational distributions of NO (A, B) can be essentially attributed to the product-pair correlations between CO (X, v″) and NO (A (2)Σ(+), v' = 0-2), NO (B (2)Π, v' = 0-2) due to energetic restriction under the vibrational distribution of CO (X, v″) produced from the vertical transition of CO (a (3)Π, v' = 0) → CO (X, v″) in the course of energy transfer. The steric opacity function has been determined at two wavelength regions: 220 < λ < 290 nm [NO (A → X) is dominant]; 320 < λ < 400 nm [NO (B → X) is dominant]. For both channels NO (A (2)Σ(+), B(2)Π), a significant CO (a (3)Π) alignment effect is recognized; the largest reactivity at the sideways direction with the small reactivity at the molecular axis direction is observed. These CO (a (3)Π) alignment effects can be essentially attributed to the steric asymmetry on two sets of molecular orbital overlap, [CO (2π) + NO (6σ (2π))] and [CO (5σ) + NO (1π (2π))]. All experimental observations support the electron exchange mechanism that is operative through the formation of a weakly bound complex OCNO.     

Quasi-classical trajectory study of the role of vibrational and translational energy in the Cl(2P) + NH3 reaction

A detailed state-to-state dynamics study was performed to analyze the effects of vibrational excitation and translational energy on the dynamics of the Cl((2)P) + NH(3)(v) gas-phase reaction, effects which are connected to such issues as mode selectivity and Polanyi's rules. This reaction evolves along two deep wells in the entry and exit channels. At low and high collision energies quasi-classical trajectory calculations were performed on an analytical potential energy surface previously developed by our group, together with a simplified model surface in which the reactant well is removed to analyze the influence of this well. While at high energy the independent vibrational excitation of all NH(3)(v) modes increases the reactivity by a factor ≈1.1-2.9 with respect to the vibrational ground-state, at low energy the opposite behaviour is found (factor ≈ 0.4-0.9). However, when the simplified model surface is used at low energy the independent vibrational excitation of all NH(3)(v) modes increases the reactivity, showing that the behaviour at low energies is a direct consequence of the existence of the reactant well. Moreover, we find that this reaction exhibits negligible mode selectivity, first because the independent excitation of the N-H symmetric and asymmetric stretch modes, which lie within 200 cm(-1) of each other, leads to reactions with similar reaction probabilities, and second because the vibrational excitation of the reactive N-H stretch mode is only partially retained in the products. For this "late transition-state" reaction, we also find that vibrational energy is more effective in driving the reaction than an equivalent amount of energy in translation, consistent with an extension of Polanyi's rules. Finally, we find that the non-reactive events, Cl((2)P)+NH(3)(v) → Cl((2)P) + NH(3)(v'), lead to a great number of populated vibrational states in the NH(3)(v') product, even starting from the NH(3)(v = 0) vibrational ground state at low energies, which is unphysical in a quantum world. This result is interpreted on the basis of non-conservation of the ZPE per mode.     

Two-photon dissociation spectroscopy of state-selected HCl+ and DCl+ ions.

HCl+ and DCl+ ions were formed via the R(1) pump line of the f3delta2(v'=0)<--sigma+(v'=0) REMPI process. For these ions, the two-photon dissociation spectroscopy, resonance-enhanced via the A2sigma+(v')<--pi3/2(v'=0) transition, was investigated for various intermediate states of HCl+ (v'=4,5,6) and DCl+ (v'=6,7,8,9). From the analysis of the data, spectroscopic parameters of the X and the A states were derived (including the lambda-doubling in the X state and the spin-rotation coupling in the A state). Some of the parameters deviate considerably from literature data. The spectra provide clear evidence that the REMPI process employed for forming the ions has a very high rotational selectivity.     

Bond and mode selectivity in the reaction of atomic chlorine with vibrationally excited CH2D2

The title reaction is investigated by co-expanding a mixture of Cl2 and CH2D2 into a vacuum chamber and initiating the reaction by photolyzing Cl2 with linearly polarized 355 nm light. Excitation of the first C-H overtone of CH2D2 leads to a preference for hydrogen abstraction over deuterium abstraction by at least a factor of 20, whereas excitation of the first C-D overtone of CH2D2 reverses this preference by at least a factor of 10. Reactions with CH2D2 prepared in a local mode containing two quanta in one C-H oscillator /2000>- or in a local mode containing one quantum each in two C-H oscillators /1100> lead to products with significantly different rotational, vibrational, and angular distributions, although the vibrational energy for each mode is nearly identical. The Cl+CH2D2/2000>- reaction yields methyl radical products primarily in their ground state, whereas the Cl+CH2D2/1100> reaction yields methyl radical products that are C-H stretch excited. The HCl(v=1) rotational distribution from the Cl+CH2D2/2000>- reaction is significantly hotter than the HCl(v=1) rotational distribution from the Cl+CH2D2/1100> reaction, and the HCl(v=1) differential cross-section (DCS) of the Cl+CH2D2/2000>- reaction is more broadly side scattered than the HCl(v=1) DCS of the Cl+CH2D2/1100> reaction. The results can be explained by a simple spectator model and by noting that the /2000>- mode leads to a wider cone of acceptance for the reaction than the /1100> mode. These measurements represent the first example of mode selectivity observed in a differential cross section, and they demonstrate that vibrational excitation can be used to direct the reaction pathway of the Cl+CH2D2 reaction.     

Two-color visible/vacuum ultraviolet photoelectron imaging dynamics of Br2

An experimental two-color photoionization dynamics study of laser-excited Br2 molecules is presented, combining pulsed visible laser excitation and tunable vacuum ultraviolet (VUV) synchrotron radiation with photoelectron imaging. The X 1Sigmag + -B 3Pi0+u transition in Br2 is excited at 527 nm corresponding predominantly to excitation of the v' = 28 vibrational level in the B 3Pi0+u state. Tunable VUV undulator radiation in the energy range of 8.40-10.15 eV is subsequently used to ionize the excited molecules to the X 2Pi32,12 state of the ion, and the ionic ground state is probed by photoelectron imaging. Similar experiments are performed using single-photon synchrotron ionization in the photon energy range of 10.75-12.50 eV without any laser excitation. Photoelectron kinetic energy distributions are extracted from the photoelectron images. In the case of two-color photoionization using resonant excitation of the intermediate B 3Pi0+u state, a broad distribution of photoelectron kinetic energies is observed, and in some cases even a bimodal distribution, which depends on the VUV photon energy. In contrast, for single-photon ionization, a single nearly Gaussian-shaped distribution is observed, which shifts to higher energy with photon energy. Simulated spectra based on Franck-Condon factors for the transitions Br2(X 1Sigmag+, v" = 0)-Br2 +(X 2Pi12,32, v+) and Br2(B 3Pi0+u, v' = 28)-Br2 +(X 2Pi12,32, v+) are generated. Comparison of these calculated spectra with the measured images suggests that the differences in the kinetic energy distributions for the two ionization processes reflect the different extensions of the vibrational wave functions in the v" = 0 electronic ground state (X 1Sigmag+) versus the electronically and vibrationally excited state (B 3Pi0+u, v' = 28).     

Accurate potential energy curve for B2. Ab initio elucidation of the experimentally elusive ground state rotation-vibration spectrum

The electron-deficient diatomic boron molecule has long puzzled scientists. As yet, the complete set of bound vibrational energy levels is far from being known, experimentally as well as theoretically. In the present ab initio study, all rotational-vibrational levels of the X (3)Σ(g)(-) ground state are determined up to the dissociation limit with near-spectroscopic accuracy (<10 cm(-1)). Two complete sets of bound vibrational levels for the (11)B(2) and (11)B-(10)B isotopomers, containing 38 and 37 levels, respectively, are reported. The results are based on a highly accurate potential energy curve, which also includes relativistic effects. The calculated set of all vibrational levels of the (11)B(2) isotopomer is compared with the few results derived from experiment [Bredohl, H.; Dubois, I.; and Nzohabonayo, P. J. Mol. Spectrosc. 1982, 93, 281; Bredohl, H.; Dubois, I.; and Melen, F. J. Mol. Spectrosc. 1987, 121, 128]. Theory agrees with experiment within 4.5 cm(-1) on average for the four vibrational level spacings that are so far known empirically. In addition, the present theoretical analysis suggests, however, that the transitions from higher electronic states to the ground state vibrational levels v = 12-15 deserve to be reanalyzed. Whereas previous experimental investigators considered them to originate from the v' = 0 vibrational level of the upper state (2)(3)Σ(u)(-), the present results make it likely that these transitions originate from a different upper state, namely the v' = 16 or the v' = 17 vibrational level of the (1)(3)Σ(u)(-) state. The ground state dissociation energy D(0) is predicted to be 23164 cm(-1).     

Interatomic potential parameters of CdHe van der Waals complex derived from excitation spectrum of the C1 1(51P1)<--X10+(51S0) vibrational transition

The first time observed excitation spectrum of the C(1)1(5(1)P(1))<--X(1)0+(5(1)S(0)) transition in CdHe van der Waals molecules is reported. Vibrational spectrum in the UV region (2286.0-2296 A) was excited in a continuous molecular-jet-expansion beam of CdHe seeded in helium using an in-house-built nitrogen-dye laser system. The excitation spectrum exhibits two vibrational components (v'<--v'=0) highly broadened by means of unresolved rotational structure and some additional contributions of "hot-bands" components (v'<--v'=1). The last effect is due to an extremely small separation of the vibrational levels in the ground X(1)0+ state of the CdHe molecule, where v'=0 vibrational level is separated from v'=0 by merely 6.0 cm(-1). It follows therefore that even in an extremely cold environment (T(v) approximately 10K) of a jet-expansion beam the population of v'=1 level is feasible, due to some residual collisions, and hence the v'<--v'=1 transitions are highly probable. The assignment of vibrational bands and numerical analysis of the spectrum was based and obtained with the aid of a rigorous computer simulation of the C(1)1<--X(1)0+ transition including the impact of rotational structure and hot-bands contributions. As a result we obtained optical potential parameters of the C(1)1(5(1)P(1)) state of CdHe molecule which are further discussed in terms of our recent (and only existing) experimental results regarding the X(1)0+, B1(5(3)P(1)) and A0+(5(3)P(1)) states of CdHe as well as in terms of ab initio calculations results.     

CH4+O(3P)→CH3+OH反应的准经典轨线研究

用准经典轨线方法研究了O（3P）与CH4的反应，计算结果表明，CH4（υ＝0，j＝0）与O（3P）的反应在低及高的碰撞参数下都是直接反应，无短寿命的碰撞复合物生成，产物OH以向后散射为主，基本上处于振转基态.CH4（υ＝1，j＝1）与O（3P）的反应在低及高的碰撞参数下反应机理不一样。在低碰撞参数下是直接反应，无短寿命的碰撞复合物生成，产物OH以向后散射为主，主要处于振动基态，转动基本上是冷的，但比高碰撞参数下的热.在高的碰撞参数下则生成短寿命的碰撞复合物，产物OH以向前散射为主，表现出明显的周边动力学反应的特征，主要处于振动激发态（υ＝1），但转动仍然是较冷的。     

Intramolecular vibrational redistribution in Ne-Br2: the signature of intermediate resonances in the excitation spectrum

Quantum-mechanical simulations of the Ne-Br(2)(B,v') excitation spectra produced after vibrational predissociation in the v'=20-35 range are reported. The aim is to investigate the signature in the excitation spectra of intermediate resonances lying in the lower v相似文献   

State-to-state dynamics of the Cl + CH3OH --> HCl + CH2OH reaction

Molecular chlorine, methanol, and helium are co-expanded into a vacuum chamber using a custom designed "late-mixing" nozzle. The title reaction is initiated by photolysis of Cl2 at 355 nm, which generates monoenergetic Cl atoms that react with CH3OH at a collision energy of 1960 +/- 170 cm(-1) (0.24 +/- 0.02 eV). Rovibrational state distributions of the nascent HCl products are obtained via 2 + 1 resonance enhanced multiphoton ionization, center-of-mass scattering distributions are measured by the core-extraction technique, and the average internal energy of the CH3OH co-products is deduced by measuring the spatial anisotropy of the HCl products. The majority (84 +/- 7%) of the HCl reaction products are formed in HCl(v = 0) with an average rotational energy of [Erot] = 390 +/- 70 cm(-1). The remaining 16 +/- 7% are formed in HCl(v = 1) and have an average rotational energy of [Erot] = 190 +/- 30 cm(-1). The HCl(v = 1) products are primarily forward scattered, and they are formed in coincidence with CH2OH products that have little internal energy. In contrast, the HCl(v = 0) products are formed in coincidence with CH2OH products that have significant internal energy. These results indicate that two or more different mechanisms are responsible for the dynamics in the Cl + CH3OH reaction. We suggest that (1) the HCl(v = 1) products are formed primarily from collisions at high impact parameter via a stripping mechanism in which the CH2OH co-products act as spectators, and (2) the HCl(v = 0) products are formed from collisions over a wide range of impact parameters, resulting in both a stripping mechanism and a rebound mechanism in which the CH2OH co-products are active participants. In all cases, the reaction of fast Cl atoms with CH3OH is with the hydrogen atoms on the methyl group, not the hydrogen on the hydroxyl group.     

Quasiclassical trajectory calculations for Li(2(2)P(J)) + H2 → LiH(X(1)Σ+) + H: influence by vibrational excitation and translational energy

Ab initio potential energy surfaces and the corresponding analytical energy functions of the ground 1A' and excited 2A' states for the Li(2(2)P) plus H(2) reaction are constructed. Quasiclassical trajectory calculations on the fitted energy functions are performed to characterize the reactions of Li(2(2)P) with H(2)(v = 0, j = 1) and H(2)(v = 1, j = 1) as well as the reaction when the vibrational energy is replaced by collision energy. For simplicity, the transition probability is assumed to be unity when the trajectories go through the crossing seam region and change to the lower surface. The calculated rotational distributions of LiH(v = 0) for both H(2)(v = 0, j = 1) and H(2)(v = 1, j = 1) reactions are single-peaked with the maximum population at j' = 7, consistent with the previous observation. The vibrational excitation of H(2)(v = 1) may enhance the reaction cross section of LiH(v' = 0) by about 200 times, as compared to a result of 93-107 reported in the experimental measurements. In contrast, the enhancement is 3.1, if the same amount of energy is deposited in the translational states. This endothermic reaction can be considered as an analog of late barrier. According to the trajectory analysis, the vibrational excitation enlarges the H-H distance in the entrance channel to facilitate the reaction, but the excess energy may not open up additional reaction configuration.     

卤化氢共振增强多光子电离光谱

测定了卤化氢(HCl, HBr 和HI) (2+1)共振增强多光子电离(REMPI)光谱, 采用模拟计算法分析推导出转动常数、谱带源以及Ω态振动谱带的同位素位移值. 得到的HCl数据同Green等人用常规分析法所推导的结果极为吻合. 得出8条振动谱带,其中包括V(¹∑⁺)态, E(¹∑⁺)的v'=4态以及HBr的5个新谱带, 此外还推导出HI的E态v'=1的4个振动谱带光谱参数. 观测了V和E态之间因同类相互作用而产生的不规则能级间距、转动参数和同位素位移. 讨论了HCl和HBr的E态和V态振动谱带中的转动谱线序列O和S对Q的强度比变化,提出了双光子激发机理.