Dynamics of ion—molecule processes: A crossed-beam study of the reaction B+(3P) + H2 → BH+ + H

Dynamics of the reaction B⁺(³P) + H₂ → BH⁺ + H has been studied in crossed-beam scattering experiments in the collision-energy range 0.6–2.3 eV (c.m.). Scattering diagrams obtained show that in the reaction both the ground state BH⁺(²Σ⁺) and the excited state BH⁺(² Π) (if energetically accessible) are formed; both states are formed via intermediate complexes whose mean lifetimes are of the order of 10^?13 s and decrease with increasing collision energy, as reflected in the decreasing forward-backward symmetry of the scattering diagrams.     

Diatomics-in-molecules correlation diagrams for (BH2)+

The diatomics-in-molecules method is applied to calculate potential energy surfaces of the system B⁺(¹S, ³P) + H₂ (X¹ Σ_g⁺. Results are presented as correlation diagrams following the approximate minimum energy paths for C_∞v and C_2v geometries of the reactants. Two possible non-adiabatic mechanisms of complex formation are discussed.     

On the reaction Si+(2P) + H2(X1Σ+g) → SiH+ + H. I. Ab initio potential energy surfaces

An ab initio unrestricted Hartree-Fock investigation on the C_∞v (1²Σ⁺, 1²Π) and C_2v (1²A₁, 1²B₁, 1²B₂) potential energy surfaces of the Si⁺ (²P) + H₂ system is presented. In the study, the MIDI-1* minimal gaussian basis set of Huzinaga and co-workers is used. The analysis of the stationary points and main features of the potential energy surfaces involved and the comparison with those of the isovalent C⁺ (²P) + H₂ → CH⁺ + H reaction reported in the literature have allowed us to understand the different dynamical behaviour exhibited by both isovalent systems near their respective threshold energies.     

An ab initio potential energy surface for the reaction N+ + H2 → NH+ + H

Preliminary results of ab initio unrestricted Hartree-Fock calculations for the potential energy surface for the reaction N⁺ + H₂ → NH⁺ + H are reported. For the collinear approach of N⁺ to H₂, the ³Σ^? surface has no activation barrier and has a shallow well (ca. 1 eV). For perpendicular approach (C_2v symmetry) the ³B₂ state is of high energy, the ³A₂ state has a shallow well but as the bond angle increases the ³B₁ state decreases in energy to become the state of lowest energy. Neither the collinear nor the perpendicular approaches give adiabatic pathways to the deep potential well of ³B₁ (HNH)⁺.     

Chemiluminescent ion-molecule reactions in the system C+ + H2

The optical emission resulting from collisions between C⁺ ions and H₂ gas was measured in the energy range 2 to 20 eV_c.m.. The observed spectrum consists mainly of the CH⁺ A ¹Π → X ¹Σ⁺ band system; CH⁺ (A ^fΠ) is shown to be formed in the chemiluminescent reactio: C⁺(²P⁰) + H₂ → CH⁺(A ¹Π) + H(²S). The energy dependence of the emission cross section was measured. The occurrence of this reaction is discussed in terms of a electronic state correlation diagram for the system.     

Electronic nonadiabatic transitions in the reactive (Ar+ + H2, Ar + H+2, ArH+ + H) system. Numerical results for the collinear configuration

In this communication are presented exact quantum mechanical nonadiabatic electronic transition probabilities for the collinear reaction Ar⁺ + H₂(v_i = 0) → ArH⁺(v_f) + H. The calculations were performed using a potential surface calculated by the DIM method. It is established that large probabilities (≈ 1.0) can be obtained only if there is enough translational energy to overcome a potential barrier formed due to the crossing between v_i = 0 of the Ar⁺ + H₂ system and v_i = 2 of the Ar + H⁺₂ system. The threshold for the reaction is found to be 0.06 eV.     

The potential energy curves of BH+

Potential energy curves for low-lying states of BH⁺ dissociating to B⁺(¹S) + H, B⁺(³P) + H and B(²P) + H⁺ have been determined by ab initio calculations. Agreement between experimental and calculated values of the spectroscopic constants for the X²Σ⁺and A²Π states supports the theoretical predictions concerning the bound B' ²Σ⁺ state. The 3²∑⁺ and 2²Π states are predicted to be repulsive.     

CEPA Calculations of potential energy surfaces for open-shell systems. II. The reaction of C+ Ions with molecular hydrogen

Ab initio calculations including electron correlation effects (mainly on CEPA-PNO level) have been performed for the potential energy surface (PES) of the reaction of ²P carbon ions with molecular hydrogen. For the collinear abstraction reactions (C_∞v symmetry: ²σ⁺, ²Π-2) the minimum energy paths have been determined. The vertical insertion reaction (C_2v; ²A₁,B₁, ²B₂) has been investigated with particular emphasis (minimum energy path, barrier heights, intersystem crossing). The influence of the size of the orbital basis and of electron correlation has been studied in some detail. The interaction of the ²A₁, and ²B₂ surfaces has been analyzed, leading to the conclusion that close to C_2v symmetry a low energy path exists by which CH₂⁺(²A₁)can be easily formed, with a barrier (²B₂ → ²A₁) ≈ 18 kcal/mol below the asymptote. The analysis of electron correlation effects reveals that it is compulsory to correlate the whole valence shell if one wants to obtain reliable surfaces. The influence of singly excited configurations for getting the correct behaviour of the PES is generally small.     

Luminescence in near-thermal charge exchange. III. CH(+) and CD(+) A → X emission from He+ C2H2 and He+ + C2D2

A pulsed ICR cell fitted with synchronous photon counting equipment is used to investigate the emission produced between 185 and 500 nm by near-thermal charge exchange between He⁺ and C₂H₂ (C₂D₂). The emission bands observed are A ²Δ → X²π and (weakly) B²Σ^? → X²π in CH(CD) and A ¹π → X¹Σ in CH⁺(CD⁺). Wavelength measurements on the bandheads of the (0,0) and (0,1) bands of CD⁺ A → X are used to evaluate vibrational constants of CH⁺(CD⁺) X¹Σ⁺. The results are (in cm^?1): ω_e = 2869 ± 27 (2106 ± 20); ω_eχ_e = 65 ± 13 (35 ± 7). These constants are used to calculate Morse-potential Franck—Condon factors and vibrational branching ratios for CH⁺ and CD⁺ A → X emission. The spectral distributions and the (relatively low) absolute emission rates produced by He⁺/C₂H₂(C₂D₂) charge exchange are briefly discussed in the light of presently available information on the charge transfer reaction and on the excited states of C₂H_2?⁺     

Laser-induced fluorescence in N2 and N+2 by multiple-photon excitation at 266 nm

The fluorescence transitions corresponding to the second positive system of N₂ (C³Π_u → B³Π_g) for Δv = 0, 1 and the first negative system of N⁺₂(B²Σ⁺_u → X²Σ⁺_g) for Δv = 0, 1, 2 have been observed following laser-induced mul excitation of N₂.     

Threshold energies for production of CH2(3B1) and CH2(1A1) from ketene photolysis. The CH2(3B1) ↔ CH2(1A1) energy splitting

By measuring the relative CO quantum yields from ketene photolysis as a function of photolysis wavelength we have determined the threshold energy at 25° for CH₂CO(¹A₁) → CH₂(³B₁) + CO(¹Σ⁺) to be 75.7 ± 1.0 kcal/mole. This corresponds to a value of 90.7 ± 1.0 kcal/mole for ΔH_f298⁰[CH₂(³B₁)]. By measuring the relative ratio of CH₂(¹A₁)/CH₂(³B₁) from ketene photolysis as a function of photolysis wavelength we have determined the threshold energy at 25°C for CH₂CO(¹A₁) → CH₂(¹A₁) + CO(¹Σ⁺) to be 84.0 ± 0.6 kcal/mole. This corresponds to a value of 99.0 ± 0.6 kcal/mole for ΔH_f298⁰[CH₂(¹A₁)]. Thus a value for the CH₂(³B₁) ? CH₂(¹A₁) energy splitting of 8.3 ± 1 kcal/mole is determined, which agrees with three other recent independent experimental estimates and the most recent quantum theoretical calculations.     

Energy distribution in CF2(1B1) from the triplet-triplet annihilation of CF2(3B1) and from the vacuum ultraviolet photolysis of C2F4

Spectral analysis of the CF₂(¹B₁) → CF₂(¹A₁) transition showed that the energy distribution found in the v₂ bending vibration (v'₂ ? 3) of CF₂(¹B₁) produced from the triplet-triplet annihilation of CF₂(³B₁) and from the vacuum ultraviolet photolysis of C₂F₄ are approximately statistical and closely related to each other.     

Yields of O2(1Σg+) and O2(1Δg) in the H + O2 reaction system,and the quenching of O2(1Σg+) by atomic hydrogen

The generation of metastable O₂(¹Σg⁺) and O₂(¹Δg) in the H + O₂ system of reactions was studied by the flow discharge chemiluminescence detection method. In addition to the O₂(¹Σg⁺) and O₂(¹Δg) emissions, strong OH(v = 2) → OH(v = 0), OH(v = 3) → OH(v = 1), HO₂(²A′₀₀₀) → HO₂(²A″₀₀₀), HO₂(²A′₀₀₁) → HO₂(²A″₀₀₀), and H O₂(²A″₂₀₀) → HO₂(²A″₀₀₀) emissions were detected in the H + O₂ system. The rate constants for the quenching of O₂(¹Σg⁺) by H and H₂ were determined to be (5.1 ± 1.4) × 10^?13 and (7.1 ± 0.1) × 10^?13 cm³ s^?1, respectively. An upper limit for the branching ratio to produce O₂(¹Σg⁺) by the H + HO₂ reaction was calculated to be 2.1%. The contributions from other reactions producing singlet oxygen were investigated.     

A theoretical ab initio SCF CI investigation of the Na + H2 reaction: The possibility of new photoreactive channels in the 4 eV region

We propose an exploratory study of the behavior of the first Rydberg states ²(4p¹) and ²(4s¹). Semiquantitative calculations (SCF + Limited CI) are used for describing the related PESs. Extended SCF CI (Moller-Plesset CIPSI algorithm) is used to characterize the important points of the reaction coordinate. The feasibility of chemical quenching yielding either NaH + H or NaH₂ starting from Rydberg states is discussed. It is shown that NaH₂ is not likely to be a stable species since the lowest minimum (linear²Σ_g⁺) is found 0.6 eV above the dissociative ²Σ_u⁺ species. Via a series of crossings a cascade from the Rydberg region to the reactive 1 ²B₂ surface is possible. Once the system is provided with the resulting extra energy, it is likely to yield chemical quenching (NaH + H) after passing through a triangular geometry. The crossing between the lowest 1²A₁ and 1²B₂ surfaces is therefore a key point for all the potential reactivity of the system.     

Quantum mechanical scattering calculations on a spline-fitted ab initio surface: the He + H+2 (ν = 0, 1, 2) → HeH+ + H reaction

All-channel time-dependent quantum mechanical reaction probabilities are reported for the collinear He + H⁺₂(ν = 0, 1, 2) → HeH⁺ + H reaction at a total energy of 1.2 eV on previously reported diatomics-in-molecule (DIM) and spline fitted ab initio (SAI) surfaces. These results are in agreement with the previous quasiclassical trajectory results in that there is vibrational enhancement of the reaction probability on the SAI surface but not on the DIM surface. This agreement lends support to our previously drawn conclusion that small differences in the potential-energy surface can lead to substantially different dynamic results.     

Laser induced photodissociation of Hn3 at 266 nm. II. Reactions of NH(1Δ) with HN3 HCl and hydrocarbon species

In the preceding paper it was shown that the 266 nm photodissociation of HN₃ gives rise to NH fragments exclusively in the vibrationless a(¹Δ) state with about 900 cm^?1 of rotational energy. These fragments collisionally react with HN₃ to produce NH₂(²A₁) in a chemiluminescent reaction. The time resolved chemiluminescence emission is used to determine the reaction rate for NH(¹Δ) + HN₃ → NH₂(²A₁) + N₃(²Π_g). The reaction rates of NH(¹Δ) with several other species, HCl, CH₄, C₂H₄, C₃H₆ and C₆H₁₂ are reported. Possible mechanisms for these reactions are considered. Condensed phase experiments are reported describing the addition reaction of NH(¹Δ) with cyclohexane.     

Preferential energy transfer from N2(A) to specific energy levels of Cu atoms

Emission spectra resulting from reaction of “clean” N₂(A³ Σ_u⁺) with copper atoms were studied using a flowing afterglow apparatus. The population distribution of the Cu states was calculated from the spectrum; it indicates that Cu atoms are excited by nearly resonant energy transfer processes. N₂(A,v') + Cu(²S_{$\text{1}\text{2}$}) → N₂(X, v) + Cu^* , and that the transfer is most efficient for N₂(A,v') → N₂(X,v) transitions with large Franck-Condon factors. The preferential energy transfer results in population inversion between some of the Cu states.     

Ab initio study of electronic energy transfer in the quenching of CO*(a 3Π) by H2

Potential energy calculations for the interaction of CO(a ³Π) with H₂(X ¹Σ_g⁺) are presented, both at the MC SCF level and with the inclusion of extensive configuration interaction. In C_2v geometry, the lowest two ³B₂ surfaces exhibit a strongly avoided crossing. At the highest level of theory used, the lowest surface provides a barrier-free adiabatic pathway for energy transfer from CO(a) to H₂, the products being CO(X ¹Σ⁺) and H₂(b ³Σ_u⁺), which dissociates to two H atoms. The energy transfer occurs by a two-electron exchange mechanism.     

Collisional ionization of fast K atoms by H2S and D2S

The process K + H₂S/D₂S → HS^?/DS^? + K⁺+ H/D has been investigated for K impact energies from near threshold to ≈100 eV. Positive and negative ion energy spectra have been obtained in the forward direction. The threshold for HS^? or DS^?production corresponds to the HS^?/DS^?+ H/D limit of the ²A₁ H₂S^?/D₂S^? state at 1.55 eV.     

Theoretical study of the mechanism for C-H bond activation in spin-forbidden reaction between Ti<Superscript>+</Superscript> and C<Subscript>2</Subscript>H<Subscript>4</Subscript>

The mechanism of the spin-forbidden reaction Ti⁺(⁴F, 3d²4s¹) + C₂H₄→TiC₂H₂ ⁺ (²A₂) + H₂ on both doublet and quartet potential energy surfaces has been investigated at the B3LYP level of theory. Crossing points between the potential energy surfaces and the possible spin inversion process are discussed by means of spin-orbit coupling (SOC) calculations. The strength of the SOC between the low-lying quartet state and the doublet state is 59.3 cm⁻¹ in the intermediate complex IM1-⁴B₂. Thus, the changes of its spin multiplicity may occur from the quartet to the doublet surface to form IM1-²A₁, leading to a sig-nificant decrease in the barrier height on the quartet PES. After the insertion intermediate IM2, two distinct reaction paths on the doublet PES have been found, i.e., a stepwise path and a concerted path. The latter is found to be the lowest energy path on the doublet PES to exothermic TiC₂H₂ ⁺(²A₂) + H₂ products, with the active barrier of 4.52 kcal/mol. In other words, this reaction proceeds in the following way: Ti⁺+C₂H₄→⁴IC→IM1-⁴B₂→^4,2ISC→IM1-²A₁→[²TS_ins]→IM2→[²TS_MCTS]→IM5→TiC₂H₂ ⁺(²A₂)+H₂. Supported by ‘Qinglan’ Talent Engineering Funds by Tianshui Normal University.