Development of a cooled He*(23S) beam source for measurements of state-resolved collision energy dependence of Penning ionization cross sections: Evidence for a stereospecific attractive well around methyl group in CH3CN

A low-temperature discharge nozzle source with a liquid-N(2) circulator for He*(2(3)S) metastable atoms has been developed in order to obtain the state-resolved collision energy dependence of Penning ionization cross sections in a low collision energy range from 20 to 80 meV. By controlling the discharge condition, we have made it possible to measure the collision energy dependence of partial ionization cross sections (CEDPICS) for a well-studied system of CH(3)CN+He*(2(3)S) in a wide energy range from 20 to 350 meV. The anisotropic interaction potential energy surface for the present system was obtained starting from an ab initio model potential via an optimization procedure based on classical trajectory calculations for the observed CEDPICS. A dominant attractive well depth was found to be 423 meV (ca. 10 kcal/mol) at a distance of 3.20 A from the center of mass of CH(3)CN in the N-atom side along the CCN axis. In addition, a weak attractive well (ca. 0.9 kcal/mol) surrounding the methyl group (-CH(3)) has been found and ascribed to the interaction between an unoccupied molecular orbital of CH(3)CN and 2s atomic orbital of He*(2(3)S).     

Anisotropic interaction and stereoreactivity in a chemi-ionization process of OCS by collision with He*(2(3)S) metastable atoms

Ionic-state-resolved collision energy dependence of Penning ionization cross sections for OCS with He*(2(3)S) metastable atoms was measured in a wide collision energy range from 20 to 350 meV. Anisotropic interaction potential for the OCS-He*(2(3)S) system was obtained by comparison of the experimental data with classical trajectory simulations. It has been found that attractive potential wells around the O and S atoms are clearly different in their directions. Around the O atom, the collinear approach is preferred (the well depth is ca. 90 meV), while the perpendicular approach is favored around the S atom (the well depth is ca. 40 meV). On the basis of the optimized potential energy surface and theoretical simulations, stereo reactivity around the O and S atoms was also investigated. The results were discussed in terms of anisotropy of the potential energy surface and the electron density distribution of molecular orbitals to be ionized.     

Penning ionization electron spectroscopy of C6H6 by collision with He*(2 3 S) metastable atoms and classical trajectory calculations: optimization of ab initio model potentials

The potential energy surface of benzene (C(6)H(6)) with a He*(2(3)S) atom was obtained by comparison of experimental data in collision-energy-resolved two-dimensional Penning ionization electron spectroscopy with classical trajectory calculations. The ab initio model interaction potentials for C(6)H(6)+He*(2(3)S) were successfully optimized by the overlap expansion method; the model potentials were effectively modified by correction terms proportional to the overlap integrals between orbitals of the interacting system, C(6)H(6) and He*(2(3)S). Classical trajectory calculations with optimized potentials gave excellent agreement with the observed collision-energy dependence of partial ionization cross sections. Important contributions to corrections were found to be due to interactions between unoccupied molecular orbitals and the He*2s orbital. A C(6)H(6) molecule attracts a He*(2(3)S) atom widely at the region where pi electrons distribute, and the interaction of -80 meV (ca. -1.8 kcal/mol) just cover the carbon hexagon. The binding energy of a C(6)H(6) molecule and a He* atom was 107 meV at a distance of 2.40 A on the sixfold axis from the center of a C(6)H(6) molecule, which is similar to that of C(6)H(6)+Li and is much larger than those of the C(6)H(6)+[He,Ne,Ar] systems.     

Collision-energy-resolved Penning ionization electron spectroscopy of p-benzoquinone: study of electronic structure and anisotropic interaction with He(*)(2 (3)S) metastable atoms

Collision energy dependence of partial ionization cross sections (CEDPICS) of p-benzoquinone with He(*)(2 (3)S) metastable atoms indicates that interaction potentials between p-benzoquinone and He(*)(2 (3)S) are highly anisotropic in the studied collision energy range (100-250 meV). Attractive interactions were found around the C==O groups for in-plane and out-of-plane directions, while repulsive interactions were found around CH bonds and the benzenoid ring. Assignment of the first four ionic states of p-benzoquinone and an analogous methyl-substituted compound was examined with CEDPICS and anisotropic distributions of the corresponding two nonbonding oxygen orbitals (n(O) (+),n(O) (-)) and two pi(CC) orbitals (pi(CC) (+),pi(CC) (-)). An extra band that shows negative CEDPICS was observed at ca. 7.2 eV in Penning ionization electron spectrum.     

Collision-energy-resolved Penning ionization electron spectroscopy of thiazole and benzothiazole: study of ionic states and anisotropic interactions between a metastable He(23S) atom and hetero cyclic compounds

Anisotropic interactions between a metastable He(2(3)S) atom and aromatic heterocyclic compounds (thiazole and benzothiazole) as well as their electronic structures were studied by means of collision-energy/electron-energy resolved two-dimensional Penning ionization electron spectroscopy combined with ab initio molecular orbital calculations. Different collision-energy dependence of partial ionization cross sections (CEDPICS) were clearly observed for different ionic states depending on anisotropic extents of molecular orbitals from which an electron is removed. It was found that thiazole and benzothiazole most strongly attract a He(2(3)S) atom around the region where the nitrogen lone pair orbital extends. For another heteroatom, sulfur, it is relatively weak, but a certain attractive interaction was found for the directions perpendicular to the molecular plane. Benzothiazole was shown to widely attract a He(2(3)S) atom in the out-of-plane directions, since the benzene moiety showed a deeper potential well than the five-membered ring. Assignments of the ionic states including shake-up states were also discussed from observed CEDPICS and ab initio molecular orbital calculations. In particular, for the satellite bands, a negative collision energy dependence of the band intensity was well supported by a configuration-interaction calculation that assigns the satellite bands to be the ionization from pi orbitals accompanying pi-pi or n-pi excitations.     

Collision-energy-resolved penning ionization electron spectroscopy of HCOOH, CH3COOH, and HCOOCH3 by collision with He*(2(3)S) metastable atoms

Penning ionization of formic acid (HCOOH), acetic acid (CH3COOH), and methyl formate (HCOOCH3) upon collision with metastable He*(2(3)S) atoms was studied by collision-energy/electron-energy-resolved two-dimensional Penning ionization electron spectroscopy (2D-PIES). Anisotropy of interaction between the target molecule and He*(2(3)S) was investigated based on the collision energy dependence of partial ionization cross sections (CEDPICS) obtained from 2D-PIES as well as ab initio molecular orbital calculations for the access of a metastable atom to the target molecule. For the interaction potential calculations, a Li atom was used in place of He*(2(3)S) metastable atom because of its well-known similarity in interaction with targets. The results indicate that in the studied collision energy range the attractive potential localizes around the oxygen atoms and that the potential well at the carbonyl oxygen atom is at least twice as much as that at the hydroxyl oxygen. Moreover we can notice that attractive potential is highly anisotropic. Repulsive interactions can be found around carbon atoms and the methyl group.     

Collision-energy-resolved penning ionization electron spectroscopy of phenylacetylene and diphenylacetylene by collision with He*(2(3)s) metastable atoms

Penning ionization of phenylacetylene and diphenylacetylene upon collision with metastable He*(2(3)S) atoms was studied by collision-energy-/electron-energy-resolved two-dimensional Penning ionization electron spectroscopy (2D-PIES). On the basis of the collision energy dependence of partial ionization cross-sections (CEDPICS) obtained from 2D-PIES as well as ab initio molecular orbital calculations for the approach of a metastable atom to the target molecule, anisotropy of interaction between the target molecule and He*(2(3)S) was investigated. For the calculations of interaction potential, a Li(2(2)S) atom was used in place of He*(2(3)S) metastable atom because of its well-known interaction behavior with various targets. The results indicate that attractive potentials localize in the pi regions of the phenyl groups as well as in the pi-conjugated regions of the acetylene group. Although similar attractive interactions were also found by the observation of CEDPICS for ionization of all pi MOs localized at the C[triple bond]C bond, the in-plane regions have repulsive potentials. Rotation of the phenyl groups about the C[triple bond]C bond can be observed for diphenylacetylene because of a low torsion barrier. So the examination of measured PIES was performed taking into consideration the change of ionization energies for conjugated molecular orbitals.     

Crossed beams study of the reaction 1CH2+C2H2-->C3H3+H

The reaction of electronically excited singlet methylene (1CH2) with acetylene (C2H2) was studied using the method of crossed molecular beams at a mean collision energy of 3.0 kcal/mol. The angular and velocity distributions of the propargyl radical (C3H3) products were measured using single photon ionization (9.6 eV) at the advanced light source. The measured distributions indicate that the mechanism involves formation of a long-lived C3H4 complex followed by simple C-H bond fission producing C3H3+H. This work, which is the first crossed beams study of a reaction involving an electronically excited polyatomic molecule, demonstrates the feasibility of crossed molecular beam studies of reactions involving 1CH2.     

Exploring the dynamics of reaction C(3P) + C2H4 with crossed beam/photoionization experiments and quantum chemical calculations

We investigated the title reaction at collision energy 3.5 kcal mol(-1) in a crossed molecular beam apparatus using undulator radiation as an ionization source. Time-of-flight (TOF) spectra of product C(3)H(3) were measured in laboratory angles from 20° to 100° using two photoionization energies 9.5 and 11.6 eV. These two sets of experimental data exhibit almost the same TOF distributions and laboratory angular distributions. From the best simulation, seven angle-specific kinetic-energy distributions and a nearly isotropic angular distribution are derived for product channel C(3)H(3) + H that has an average kinetic-energy release of 15.5 kcal mol(-1), corresponding to an average internal energy of 33.3 kcal mol(-1) in C(3)H(3). Furthermore, TOF spectra of product C(3)H(3) were measured at laboratory angle 52° with ionizing photon energies from 7 to 12 eV. The appearance of TOF spectra remains almost the same, indicating that a species exclusively contributes to product C(3)H(3); the species is identified as H(2)CCCH (propargyl) based on the ionization energy of 8.6 ± 0.2 eV and the maximal kinetic-energy release of 49 kcal mol(-1). Theoretical calculations indicate that the rapid inversion mechanism and rotation in intermediate H(2)CCCH(2) can result in a forward-backward symmetric angular distribution for product C(3)H(3) + H. The present work avoids the interference of reactions of C((1)D) and C(2) radicals with C(2)H(4) and rules out the probability of production of other isomers like c-C(3)H(3) and H(3)CCC proposed in the previous work at least at the investigated collision energy.     

Angle-energy distributions of Penning ions in crossed molecular beams. IV. He*(21 S,2 3S)+H2-->He+H2+ +e-

Relative doubly differential cross sections for the Penning ionization of H(2) by spin-state-selected metastable He (1s2s) are reported at center-of-mass collision energies E of 3.1 and 4.2 kcal/mol in a crossed supersonic beam experiment employing a rotatable mass spectrometer detector. The measurements are sufficiently dense in velocity space as to avoid having to functionalize the differential cross sections in order to transform the intensities into the c.m. The H(2) (+) product is scattered sharply forward, c.m. Deltatheta<10 degrees half-width at half-maximum, with respect to the incident direction of H(2) at both energies for both spin states. On the average the products have lost energy upon recoil, mean recoil energy E(')相似文献   

Potential surfaces and dynamics of the O(3P)+H2O(X1A1)-->OH(X2pi)+OH(X2pi) reaction

We present global potential energy surfaces for the three lowest triplet states in O(3P)+H2O(X1A1) collisions and present results of classical dynamics calculations on the O(3P)+H2O(X1A1)-->OH(X2pi)+OH(X2pi) reaction using these surfaces. The surfaces are spline-based fits of approximately 20,000 fixed geometry ab initio calculations at the complete-active-space self-consistent field+second-order perturbation theory (CASSCF+MP2) level with a O(4s3p2d1f)/H(3s2p) one electron basis set. Computed rate constants compare well to measurements in the 1000-2500 K range using these surfaces. We also compute the total, rovibrationally resolved, and differential angular cross sections at fixed collision velocities from near threshold at approximately 4 km s(-1) (16.9 kcal mol(-1) collision energy) to 11 km s(-1) (122.5 kcal mol(-1) collision energy), and we compare these computed cross sections to available space-based and laboratory data. A major finding of the present work is that above approximately 40 kcal mol(-1) collision energy rovibrationally excited OH(X2pi) products are a significant and perhaps dominant contributor to the observed 1-5 micro spectral emission from O(3P)+H2O(X1A1) collisions. Another important result is that OH(X2pi) products are formed in two distinct rovibrational distributions. The "active" OH products are formed with the reagent O atom, and their rovibrational distributions are extremely hot. The remaining "spectator" OH is relatively rovibrationally cold. For the active OH, rotational energy is dominant at all collision velocities, but the opposite holds for the spectator OH. Summed over both OH products, below approximately 50 kcal mol(-1) collision energy, vibration dominates the OH internal energy, and above approximately 50 kcal mol(-1) rotation is greater than vibrational energy. As the collision energy increases, energy is diverted from vibration to mostly translational energy. We note that the present fitted surfaces can also be used to investigate direct collisional excitation of H2O(X1A1) by O(3P) and also OH(X2pi)+OH(X2pi) collisions.     

Ring opening of 2,5-didehydrothiophene: structures and rearrangements of C4H2S isomers

Electronic structures and rearrangement pathways of several C4H2S isomers are computationally investigated by methods based on coupled cluster theory and density functional theory. Six singlet C4H2S isomers lie within ca. 30 kcal/mol above butatrienethione (6), the apparent global minimum. Ethynylthioketene (7) lies only 2 kcal/mol higher in energy than cumulene 6. Two open-chain isomers, butadiynylthiol (8) and diethynyl sulfide (9), reside ca. 9 and 24 kcal/mol above 6, respectively. Lying 30 kcal/mol above 6, two cyclic singlet isomers, ethynylthiirene (10) and cyclopropenylidenemethanthione (11), are nearly degenerate in energy. Thiophene-2,5-diyl (12) lies substantially higher in energy than 6 (ca. 45 kcal/mol) and is predicted to rearrange preferentially by C-S bond cleavage, leading to thioketene 7, rather than by C-C bond cleavage, leading to diethynyl sulfide (9; retro-Bergman cyclization). Accurate spectroscopic properties of these C4H2S isomers, as well as an understanding of their rearrangement pathways, should facilitate the detection and characterization of these isomers in the laboratory and the interstellar medium.     

Collision-energy-resolved Penning ionization electron spectroscopy of bromomethanes (CH3Br, CH2Br2, and CHBr3) by collision with He*(2(3)S) metastable atoms

Ionization of bromomethanes (CH3Br, CH2Br2, and CHBr3) upon collision with metastable He*(2(3)S) atoms has been studied by means of collision-energy-resolved Penning ionization electron spectroscopy. Lone-pair (nBr) orbitals of Br4p characters have larger ionization cross sections than sigma(C-Br) orbitals. The collision-energy dependence of the partial ionization cross sections shows that the interaction potential between the molecule and the He*(2(3)S) atom is highly anisotropic around CH3Br or CH2Br2, while isotropic attractive interactions are found for CHBr3. Bands observed at electron energies of approximately 2 eV in the He*(2(3)S) Penning ionization electron spectra (PIES) of CH2Br2 and CHBr3 have no counterpart in ultraviolet (He I) photoionization spectra and theoretical (third-order algebraic diagrammatic construction) one-electron and shake-up ionization spectra. Energy analysis of the processes involved demonstrates that these bands and further bands overlapping with sigma(C-Br) or piCH2 levels are related to autoionization of dissociating (He+ - Br-) pairs. Similarly, a band at an electron energy of approximately 1 eV in the He*(2(3)S) PIES spectra of CH3Br has been ascribed to autoionizing Br** atoms released by dissociation of (unidentified) excited states of the target molecule. A further autoionization (S) band can be discerned at approximately 1 eV below the lone-pair nBr bands in the He*(2(3)S) PIES spectrum of CHBr3. This band has been ascribed to the decay of autoionizing Rydberg states of the target molecule (M**) into vibrationally excited states of the molecular ion. It was found that for this transition, the interaction potential that prevails in the entrance channel is merely attractive.     

Theoretical study of the C6H3 potential energy surface and rate constants and product branching ratios of the C2H(2Sigma+) + C4H2(1Sigma(g)+) and C4H(2Sigma+) + C2H2(1Sigma(g)+) reactions

Ab initio CCSD(T)cc-pVTZ//B3LYP6-311G(**) and CCSD(T)/complete basis set (CBS) calculations of stationary points on the C(6)H(3) potential energy surface have been performed to investigate the reaction mechanism of C(2)H with diacetylene and C(4)H with acetylene. Totally, 25 different C(6)H(3) isomers and 40 transition states are located and all possible bimolecular decomposition products are also characterized. 1,2,3- and 1,2,4-tridehydrobenzene and H(2)CCCCCCH isomers are found to be the most stable thermodynamically residing 77.2, 75.1, and 75.7 kcal/mol lower in energy than C(2)H + C(4)H(2), respectively, at the CCSD(T)/CBS level of theory. The results show that the most favorable C(2)H + C(4)H(2) entrance channel is C(2)H addition to a terminal carbon of C(4)H(2) producing HCCCHCCCH, 70.2 kcal/mol below the reactants. This adduct loses a hydrogen atom from the nonterminal position to give the HCCCCCCH (triacetylene) product exothermic by 29.7 kcal/mol via an exit barrier of 5.3 kcal/mol. Based on Rice-Ramsperger-Kassel-Marcus calculations under single-collision conditions, triacetylene+H are concluded to be the only reaction products, with more than 98% of them formed directly from HCCCHCCCH. The C(2)H + C(4)H(2) reaction rate constants calculated by employing canonical variational transition state theory are found to be similar to those for the related C(2)H + C(2)H(2) reaction in the order of magnitude of 10(-10) cm(3) molecule(-1) s(-1) for T = 298-63 K, and to show a negative temperature dependence at low T. A general mechanism for the growth of polyyne chains involving C(2)H + H(C[triple bond]C)(n)H --> H(C[triple bond]C)(n+1)H + H reactions has been suggested based on a comparison of the reactions of ethynyl radical with acetylene and diacetylene. The C(4)H + C(2)H(2) reaction is also predicted to readily produce triacetylene + H via barrierless C(4)H addition to acetylene, followed by H elimination.     

Electronic structure of H2CS3 and H2CS4: an experimental and theoretical study

The HeI photoelectron spectra of H2CS3 and H2CS4 in the gas phase have been obtained for the first time. A complete theoretical study involving the calculation of the ionization energies using orbital valence Green's functional (OVGF) and population analysis was performed. Calculations of cation-radical forms were carried out in order to interpret the main characters of the six highest occupied molecular orbitals (HOMOs). The first vertical ionization potentials are 8.74 and 8.56eV for H2CS3 and H2CS4, and attributed to {9b2(nS(C=S))}-1 and {8a"(3ppi*(S-S), nS)}-1, respectively. Meanwhile, the energy sequence of three types of sulfur 3p lone-pair have been discussed: 3ppi(S-S)*相似文献   

Rotationally resolved reactive scattering: imaging detailed Cl+C2H6 reaction dynamics

The hydrogen atom abstraction reaction of Cl (2P3/2) with ethane has been studied using the crossed molecular beam technique with dc slice imaging at collision energies from 3.2 to 10.4 kcal/mol. The products HCl (v,J) (v = 0, J = 0-5) were state-selectively detected using 2+1 resonance enhanced multiphoton ionization. The images were used to obtain the center-of-mass frame product angular distributions and translational energy release distributions. Two general features were found in all probed HCl quantum states at 6.7 kcal/mol collision energy, and these features have distinct translational energy release and angular distributions, as described for HCl (v = 0, J = 2) in a recent preliminary report [Li et al., J. Chem. Phys. 124, 011102 (2006)]. The results for HCl (v = 0, J = 2) at four collision energies were also compared to investigate the energy-dependent dynamics. We discuss the reaction in terms of a variety of models of polyatomic reaction dynamics. The dynamics of this well studied system are more complicated than can be accounted for by a single mechanism, and the results call for further theoretical and experimental investigations.     

Probing the shape and stereochemistry of molecular orbitals in locally flexible aromatic chains: a penning ionization electron spectroscopy and Green's function study of the electronic structure of biphenyl

We report on the results of an exhaustive study of the interplay between the valence electronic structure, the topology and reactivity of orbitals, and the molecular structure of biphenyl by means of Penning ionization electron spectroscopy in the gas phase upon collision with metastable He*(2(3)S) atoms. The measurements are compared with one-particle Green's function calculations of one-electron and shake-up valence ionization spectra employing the third-order algebraic diagrammatic construction scheme [ADC(3)]. Penning ionization intensities are also analyzed by means of the exterior electron-density model and comparison with photoelectron spectra: in contrast with the lines originating from sigma orbitals, ionization lines belonging to the pi-band system have large Penning ionization cross sections due to their greater extent outside the molecular van der Waals surface. The involved chemi-ionization processes are further experimentally investigated using collision-energy-resolved Penning ionization electron spectroscopy. The cross sections of pi-ionization bands exhibit a markedly negative collision-energy dependence and indicate that the interaction potential that prevails between the molecule and the He*(2(3)S) atom is strongly attractive in the pi-orbital region. On the other hand, the partial ionization cross sections pertaining to sigma-ionization channels are characterized by more limited collision-energy dependencies, as a consequence of rather repulsive interactions within the sigma-orbital region. A comparison of ADC(3) simulations with the Penning ionization electron spectra and UV photoelectron spectra measured by Kubota et al. [Chem. Phys. Lett. 1980, 74, 409] on thin films of biphenyl deposited at 170 and 109 K on copper demonstrates that biphenyl molecules lying at the surface of polycrystalline layers adopt predominantly a planar configuration, whereas within an amorphous sample most molecules have twisted structures similar to those prevailing in the gas phase.     

Interaction of porphine and its metal complexes with C60 fullerene: a DFT study

We performed DFT calculations (BLYP general-gradient approximation in conjunction with a double numerical basis set) for the interaction of free porphine ligand and a number of its metal complexes with C60 molecule to analyze how the nature of a central metal ion influences the geometry and electronic characteristics (electrostatic potential and spin density distribution and highest-occupied molecular orbital (HOMO) and lowest-unoccupied molecular orbital (LUMO) structure). We found that the presence of a central metal ion is crucial for a strong interaction. The energy of interaction between H2P and C60 is -0.3 kcal mol(-1) only, whereas the formation energies for the metal complexes vary from -27.3 kcal mol(-1) for MnClP.C60 to -45.8 kcal mol(-1) for MnP.C60. As a rule, the formation energy correlates with the separations between porphinate and fullerene molecules; the Mn and Fe complexes exhibit the closest approach of ca. 2.2 A between the metal ion and carbon atoms of C60. In most porphine-C60 complexes studied, the two closest contacts of central metal ion or H are those with carbon atoms of the (6,6) bond; VOP.C60 is the only exception, where the closest V...C contacts involve the (5,6) bond. The macrocycle geometry changes, and the magnitude of the effect depends on the central atom, being especially dramatic for Mn, MnCl, and Fe complexes. The shape of LUMOs in most complexes with C60 is not affected notably as compared to the LUMO of the isolated C60 molecule. In the case of Fe, the HOMO extends from the central atom to two opposite pyrrol rings. At the same time, the HOMO-LUMO gap energy decreases drastically in most cases, by ca. 20-30 kcal mol(-1). For electrostatic potential distribution, we systematically observed that the negative lobe contacting C60 shrinks, whereas the opposite one becomes notably bigger. In the case of paramagnetic complexes of VO, Mn, FeCl, Co, and Cu, spin density distribution was analyzed as well.     

Ab initio potential energy surfaces of the ion-molecule reaction: C2H2 + O+

High level ab initio calculations using complete active space self-consistent field and multi reference single and double excitation configuration interaction methods with cc-pVDZ (correlation consistent polarized valence double zeta) and cc-pVTZ (triple zeta) basis sets have been performed to elucidate the reaction mechanism of the ion-molecule reaction, C2H2(1Sigmag+) + O+(4S), for which collision experiment has been performed by Chiu et al. [J. Chem. Phys. 109, 5300 (1998)]. The minor low-energy process leading to the weak spin-forbidden product C2H2+ (2Piu) + O(1D) has been studied previously and will not be discussed here. The major pathways to form charge-transfer (CT) products, C2H2+ (2Piu) + O(3P) (CT1) and C2H2+ (4A2) + O(3P) (CT2), and the covalently bound intermediates are investigated. The approach of the oxygen atom cation to acetylene goes over an energy barrier TS1 of 29 kcal/mol (relative to the reactant) and adiabatically leads the CT2 product or a weakly bound intermediate Int1 between CT2 products. This transition state TS1 is caused by the avoided crossing between the reactant and CT2 electronic states. As the C-O distance becomes shorter beyond the above intermediate, the C1 reaction pathway is energetically more favorable than the Cs pathway and goes over the second transition state TS2 of a relative energy of 39 kcal/mol. Although this TS connects diabatically to the covalent intermediate Int2, there are many states that interact adiabatically with this diabatic state and these lead to the other charge-transfer product CT1 via either of several nonadiabatic transitions. These findings are consistent with the experiment, in which charge transfer and chemical reaction products are detected above 35 and 39 kcal/mol collision energies, respectively.