Ab Initio Study of Electron Capture in Collisions of Protons with CO Molecules.

Ab initio calculations of cross sections for electron capture by protons in collisions with CO are carried out at energies between 100 eV/u and 50 keV/u, employing a semiclassical method within the Franck-Condon framework. The scattering wave function is expanded in a set of ab initio electronic wave functions of the HCO supermolecule. The calculation is performed on several trajectory orientations to obtain orientation-averaged total cross sections.

HO˙ and OH reactivity furan: experimental low energy absolute cross sections for modeling radiation damage.

Radiotherapy is one of the most widespread and efficient strategies to fight malignant tumors. Despite its broad application, the mechanisms of radiation-DNA interaction are still under investigation. Theoretical models to predict the effects of a particular delivered dose are still in their infancy due to the difficulty of simulating a real cell environment, as well as the inclusion of a large variety of secondary processes.

Resonant Fragmentation of the Water Cation by Electron Impact: a Wave-Packet Study.

We have investigated the dissociation of a resonant state that can be formed in low energy electron scattering from H O . We have chosen the second triplet resonance above the state of H O whose autoionization mainly produces H O ( ). We have considered both dissociation of the resonant state itself, dissociative recombination (DR), or the dissociation of the H O cation after autodetachment, dissociative excitation (DE).

Charge Transfer and Electron Production in Proton Collisions with Uracil: A Classical and Semiclassical Study.

Cross sections for charge transfer and ionization in proton-uracil collisions are studied, for collision energies 0.05 View Article and Find Full Text PDF

A classical and semiclassical study of collisions between X ions and water molecules.

Collisions of He, Li and C ions with water molecules are studied at energies ranging between 20 keV u and 500 keV u. Three methods are employed: the classical trajectory Monte Carlo (CTMC), the expansion of the scattering wave function in terms of asymptotic frozen molecular orbitals (AFMO) and a lattice method to numerically solve the time-dependent Schrödinger equation (GridTDSE). Total cross sections for single ionization, single electron capture, transfer ionization and electron production are calculated and compared with previous close-coupling calculations and experiments.

Nonadiabatic fragmentation of HO and isotopomers. Wave packet propagation using ab initio wavefunctions.

The fragmentation of the water cation from its B[combining tilde] 2B2 electronic state, allowing the participation of the X[combining tilde] 2B1, Ã 2A1 and C[combining tilde] 2B1 states in the process, is simulated using the extended capabilities of the collocation GridTDSE code to account for the nonadiabatic propagation of wave packets in several potential energy surfaces connected by nonadiabatic couplings. Molecular data are calculated ab initio. Two initial wave packets are considered to reproduce two different experiments.

Ionization and Single and Double Electron Capture in Proton-Ar Collisions.

Total cross sections for formation of H and H, and electron production, in H + Ar collisions have been calculated at energies between 100 eV and 200 keV by employing two methods: for E < 10 keV, a semiclassical treatment with an expansion in a basis of electronic wave functions of the ArH quasimolecule and, for E > 10 keV, the switching-classical-trajectory-Monte Carlo method (s-CTMC). The semiclassical calculation involves transitions to molecular autoionizing states, calculated by applying a block-diagonalization technique. The s-CTMC method is adept to treat two-electron processes and yields total cross sections for H formation in reasonably good agreement with the experimental data.

Nonadiabatic Quantum Dynamics Predissociation of H2O(+)(B̃ (2)B2).

A quantum-mechanical study of the predissociation of H2O(+) (B̃ (2)B2) is carried out by using wave packet propagations on ab initio potential energy surfaces connected by nonadiabatic couplings. The simulations show that within the first 30 fs 80% of the initial wave packet is transferred from the B̃ (2)B2 to the à (2)A1 electronic state through a conical intersection. A much slower transfer (in the ps time scale) from the à(2)A1 to the X̃ (2)B1 state due to a Renner-Teller coupling determines the fragmentation branching ratios, which are in accordance with the experimental measurements.

New light shed on charge transfer in fundamental H+ + H2 collisions.

There is no consensus on the magnitude and shape of the charge transfer cross section in low-energy H+ + H2 collisions, in spite of the fundamental importance of these collisions. Experiments have thus been carried out in the energy range 15≤E≤5000  eV. The measurements invalidate previous recommended data for E≤200  eV and confirm the existence of a local maximum around 45 eV, which was predicted theoretically.

Ionization and electron capture in ion-molecule collisions: classical (CTMC) and semiclassical calculations.

Total cross-sections for electron capture and electron production in proton collisions with N2, CO and H2O, are evaluated using a classical trajectory Monte Carlo treatment for collision energies between 30 and 3000 keV. A semiclassical close-coupling treatment has been also employed for proton collisions with H2O, to discuss the accuracy of the CTMC treatment. Singly differential cross-sections for electron production have been also evaluated.

Influence of nuclear exchange on nonadiabatic electron processes in H(+)+H2 collisions.

H(+)+H(2) collisions are studied by means of a semiclassical approach that explicitly accounts for nuclear rearrangement channels in nonadiabatic electron processes. A set of classical trajectories is used to describe the nuclear motion, while the electronic degrees of freedom are treated quantum mechanically in terms of a three-state expansion of the collision wavefunction. We describe electron capture and vibrational excitation, which can also involve nuclear exchange and dissociation, in the E = 2-1000 eV impact energy range.

A study of conical intersections for the H3(+) system.

A parametrization of the three asymptotic conical intersections between the energies of the H3(+) ground state and the first excited singlet state is presented. The influence of an additional, fourth conical intersection between the first and second excited states at the equilateral geometry on the connection between the three conical regions is studied, for both diatomics-in-molecules and ab initio molecular data.

Study of ab initio molecular data for inelastic and reactive collisions involving the H3+ quasimolecule.

The lowest two ab initio potential energy surfaces (PES), and the corresponding nonadiabatic couplings between them, have been obtained for the H3+ system; the molecular data are compared to those calculated with the diatomic in molecules (DIM) method. The form of the couplings is discussed in terms of the topology of the molecular structure of the triatomic. The method of Baer is employed to generate "diabatic" states and the residual nonadiabatic couplings are calculated.

Sign-consistent dynamical couplings between ab initio three-center wave functions.

We present a method to ensure the sign consistency of dynamical couplings between ab initio three-center wave functions. The method also allows to systematically "diabatize" avoided crossings between two potential energy surfaces, including conical intersections. Illustrations are presented for H(3)(+), LiH(2)(+), and NH(2)(5+) quasimolecules.