Edward F. Hayes

Nonempirical LCAO–MO–SCF Study of the Energy Surface for Linear HeH2+

The nonempirical LCAO–SCF–MO method using a contracted Gaussian basis is used to generate a potential energy surface for the ground state of the linear HeH2+ system. Recently, Chupka, Berkowitz, and Russell reported that even above threshold the cross sections for the reaction H2++He=HeH++H, are strongly dependent on the vibrational state of the H2+ ion. Examination of the calculated potential‐energy surface for this reaction reveals that the energy barrier for this reaction occurs very late in the exit channel. This result, coupled with the work of Polanyi and Wong on the effect of the position of the potential‐energy barrier, suggests that this late energy barrier is the reason that vibrational energy is much more effective than translational energy in causing this reaction. Another interesting feature of the calculated potential energy surface is the presence of a minimum corresponding to a HeH2+ complex. Investigation of the energy of this complex as a function of He–H–H bond angle demonstrates that t...

Nonempirical LCAO MO SCF studies of the group IIa dihalides BeF2, MgF2, and CaF2

Nonempirical LCAO MO SCF calculations are reported for the ground, C2ν states of the Group IIa dihalides, BeF2, MgF2, and CaF2. These calculations demonstrate the importance of 3d orbitals in the bonding trends of the dihalides and, hence, in the determination of the equilibrium bond angles and the bending force constants. The calculations on BeF2 indicate that d orbitals play an important role in the bonding but do not preferentially alter the general features of the total energy curve at any bond angle. In the case of MgF2, d orbitals are found to preferentially lower the energy of the nonlinear configurations. However, for both species, the ground‐state equilibrium bond angle is predicted to be 180°. Configuration interaction studies also support the fact that, in the gas phase, the linear configuration is most stable. On the basis of s(1s, 2s, 3s, 4s, 2p, and 3p orbitals on Ca) basis set calculations, it is predicted that CaF2 is linear. However, when 3d orbitals are added to the s basis set, the pred...

Accurate three‐dimensional quantum scattering studies of long‐lived resonances for the reaction He+H+2→HeH++H

The adiabatically adjusting principal‐axis hyperspherical (APH) formulation of Pack and Parker for quantum reactive scattering in three dimensions (3D) is used to obtain converged results for the reaction of helium with H+2 (v=1–4) for total angular momentum J=0. The ab initio potential energy surface computed by McLaughlin and Thompson and fitted by Joseph and Sathyamurthy is utilized for the HeH+2 interaction potential. The predicted energy dependence of the accurate 3D state‐to‐state reaction probabilities show clear evidence for quantum resonances. These resonances are even more numerous than those reported earlier for reduced dimensionality studies of this reaction. The calculated time delays for several of these resonances are found to be over 1 ps. Bending corrected rotating linear model (BCRLM) studies of this same reaction are also reported. These results provide useful insight in sorting out the nature and contribution of the resonances found in the 3D studies.

Integral equation approach to collinear reactive scattering: A + BC → AB + C

An integral equation approach to collinear reactive scattering has been developed. The technique has been implemented on a computer for calculation of scattering matrices for the following reactions: H+H2→H2+H; D+H2→HD+H; and F+H2→HF+H. The results of these calculations are found to be in good agreement with those obtained by earlier workers. The attractive features of this method are discussed.

Nonempirical LCAO MO SCF and CI Studies of the Low Lying Electronic State of the HOO Radical

Nonempirical LCAO MO SCF and configuration interaction calculations are reported for the ground state and the low lying 2A′ state of HO2. The first excited 2A′ state of HO2 is found to be approximately 17 kcal above the ground state. The correlation diagram for the reaction H+O2⇌OH+O and the importance of the low lying 2A′ state of HO2 are discussed.

Open and closed channel resonances in the collinear inelastic scattering of He by H+2

Collinear quantum mechanical calculations are reported for the inelastic scattering of He by H+2 at energies below the reaction threshold. The inelastic transition probability curves show pronounced quantum oscillations as a function of energy due to both open and closed channel resonances. An analysis of these resonances indicates that the open channel resonance is associated with tunneling through a small barrier and the closed channel resonance is a Feshbach or compound state resonance corresponding to vibrational excitation of H+2 to a closed vibrational state. The compound state resonances are similar to those found earlier to be important in the reaction He+H+2→HeH++H.

Resonances in the collinear inelastic scattering of He by H+2 below the reaction threshold

Collinear quantum mechanical calculations are reported for the inelastic scattering of He by H+2 below the reaction threshold. The inelastic transition probability curves show a severe oscillatory behavior similar to that recently observed in reaction probability curves for this same system. Perturbation calculations and considerations of the channel phase shifts indicate that the resonance structure is caused by the existence of quasibound (resonance) states of HeH+2. A simple picture is presented which accounts for these quasibound states.

Quantum Mechanical Studies of the Vibrational Excitation of H2 by Li

The quantum mechanical equations of motion for the vibrational excitation of an harmonic are solved via the set of coupled Volterra equations describing that motion. The numerical techniques which allow accurate inclusion of closed channels are developed. The equations are solved for an ab initio interaction potential and for a model potential. The ab initio interaction potential gives results in poor agreement with experiments. A comparison with the results of a two‐parameter model potential, which can give results close to the experimental results, provides some insight into features of the surface which are important for vibration excitation.

Theoretical Study of the Barriers to Internal Rotation in Formic Acid

Nitrous acid, HONO, has been studied for three geometries by the ab initio LCAO SCF MO method with a basis of accurate gaussian atomic orbitals. The trans geometry is correctly predicted to be most stable, lying about 2 kcal/mole lower than the cis form, and 9 kcal/mole lower than the 90° form (experimental estimates being 0.4 and 11.6 kcal/mole, respectively). Population analysis, dipole moment components, and properties related to nuclear-nuclear and nuclear-electron potentials all show a partial breaking of the hydroxyl oxygen-nitrogen bond at 90° compared to cis and trans, as well as the effects of electronic rearrangement for nuclear screening in the high nuclear repulsion cis form. The cis to 90° barrier is dominated by the attractive components of the total energy, while the trans to 90° one is dominated by repulsive components, in agreement with our analysis and an earlier prediction by Allen.

Quasiclassical trajectory calculations compared to quantum mechanical reaction probabilities, rate constants, and activation energies for two different potential surfaces for the collinear reaction H2+I→H+HI, including dependence on initial vibrational state

Quantum mechanical calculations are compared to quasiclassical trajectory forward (QCT) calculations for the collinear, endoergic reaction H2(n1)+I→H+HI for two different potential energy surfaces, a rotated‐Morse‐curve (RMC) surface and the semiempirical valence‐bond surface of Raff et al. Vibrationally state‐selected reaction probabilities and rate constants and Arrhenius parameters are presented. Thermally averaged rate constants and their Arrhenius parameters are also given. For one of the potential energy surfaces, quasiclassical trajectory reverse histogram (QCTRH) calculations were also performed. The results show that classical mechanics and quantum mechanics are in significant qualitative agreement for state‐selected properties. Specifically, for the n1=0 state of the Raff et al. surface the quantum mechanical reaction probabilities are very small (less than 0.005) and the QCT method predicts this state to be totally non‐reactive. For all other states on both surfaces quantum mechanics and QCT an...