Tasko P. Grozdanov

Low-energy H+ + H2 reactive collisions: mean-potential statistical model and role of permutation symmetry.

Statistical theory based on a mean isotropic potential deduced from a full potential energy surface is applied to the complex-forming, reactive H(+) + H(2) system in the interval of collision energies E(c) = 10(-3) to 0.5 eV. We present expressions for the reaction probabilities that incorporate the full permutation symmetry of the protons and compare our results with other statistical models and full quantum mechanical approaches that take account this symmetry correctly, approximately, or erroneously for the exchange rearrangement mechanism of the reaction.

Mean potential statistical theory of the H+ + D2 → HD + D+ reaction.

The reactive collision process H(+) + D(2)(ν = 0, j = 0) → HD + D(+) is theoretically analyzed for collision energies ranging from threshold up to 1.3 eV. It is assumed that the reaction takes place via formation of a collision complex. In calculations, a statistical theory is used, based on a mean isotropic potential deduced from a full potential energy surface. Calculated integral cross sections, opacity functions, and rotational distributions of the HD products are compared with recent statistical and quantum mechanical calculations performed using a full potential energy surface. Satisfactory agreement between the results obtained using the two statistical methods is found, both of which however overestimate the existing quantum mechanical predictions. The effects due to the presence of identical particles are also discussed.

Calculations of near-threshold cross sections for photodissociation of CH+ using the Lanczos algorithm

We combine the Lanczos algorithm with the absorbing-potential method, implemented in a discrete variable representation to calculate the near-threshold photodissociation cross sections of CH+. The method is iterative, based on a continued fraction representation of the Green function and avoids any explicit matrix diagonalization. A very good agreement is found with experiment and close-coupling calculations.

Use of a recursive expansion of the Green operator with absorbing boundary conditions to study the effect of non-adiabatic coupling on photodissociation cross sections: application to the CO molecule

The recently proposed iterative method (Grozdanov T P and McCarroll R 1996 J. Phys. B: At. Mol. Opt. Phys. 29 3373) for calculating the total photodissociation cross sections, based on a recursive expansion of the Green operator with absorbing boundary conditions, is applied to the case where the final electronic states are coupled leading to predissociation. The process considered is the transition of the CO molecule from the ground X 1+ state into Rydberg-valence predissociating B 1+-D´ 1+ states. Agreement with close coupling calculations is found.

Comparison of various L2 methods for calculations of radiative association cross sections: Application to collisions of Li with H+

The performance of three different L2 methods are tested in calculations of radiative association cross sections in collisions of Li with H+. The first two methods, the smooth-exterior-complex-scaling method and a method using complex absorbing potentials, are based on the direct determination of poles of the Green function and are superior at low collision energies where narrow shape resonances dominate. The third method, based on the iterative Chebyshev-polynomial expansion of the Green function, is efficient only at higher energies where the cross sections are smooth functions of the collision energy.

Calculations of photodissociation and photoionization cross sections by using a recursive expansion of Green's operator with absorbing boundary conditions

An iterative method for calculating total cross sections for molecular photodissociation and atomic photoionization is presented. It is based on the recursive expansion of Greens operator with absorbing boundary conditions, recently developed by Mandelshtam and Taylor. The method is tested by calculating cross sections for photodissociation of the molecule and another model problem, as well as for the photoionization of a hydrogen atom in the absence and presence of a strong magnetic field. In all applications the discrete variable representation is employed.

Calculations of partial cross sections for photofragmentation processes using complex absorbing potentials

We investigate the use of complex absorbing potentials for the calculation of partial cross sections in multichannel photofragmentation processes. An exactly solvable, coupled-two-channel problem involving square-well potentials is used to compare the performance of various types of absorbing potentials. Special emphasis is given to the near-threshold regions and the conditions under which the numerical results are able to reproduce the Wigner threshold laws. It was found that singular, transmission-free absorbing potentials perform better than those of power or polynomial form.

Calculations of photodissociation cross sections using the Lanczos algorithm

We combine the Lanczos algorithm with both the smooth-external-complex-scaling method and the absorbing-potential method, implemented in the discrete variable representation to calculate the photodissociation cross sections. The method is iterative, based on a continued fraction representation of the Green function and avoids any matrix diagonalization. The problems of the stability and convergence of the method are studied using a model calculation as well as calculating the photodissociation cross sections of the CO molecule involving non-adiabatic coupling of two states.

Iterative calculations of photoionization cross sections by using the Lanczos algorithm and the complex coordinate method in the discrete variable representation

Abstract The combination of the Lanczos algorithm and the complex coordinate method, implemented in the discrete variable representation is used to obtain directly the complete photoabsorption spectrum in a single calculation. The method is iterative, based on the continued fraction representation of the Green function. Test calculations of the cross sections for photoionization of hydrogen, lithium and sodium atoms are presented. The convergence properties of the method are discussed.

Calculations of photodissociation cross sections by the smooth exterior complex scaling method

Abstract We show that total photodissociation cross sections can be calculated directly by the smooth exterior complex scaling method. First, an application to a model problem, characterized by the resonance-dominated cross section is considered, in which the detailed comparisons with approaches employing the standard complex scaling and the complex absorbing potentials are made. Second, the photodissociation cross sections for transitions from the ground vibrational state of the X 2 Π electronic state of HCl + to the continua of the (2) 2 Π and (3) 2 Π states are calculated, by using a discrete set of realistic molecular data.