Paul L. Devries

Quantum-mechanical theory including angular momenta analysis of atom-atom collisions in a laser field

The problem of two atoms colliding in the presence of an intense radiation field, such as that of a laser, is investigated. The radiation field, which couples states of different electronic symmetry, is described by the number state representation while the electronic degrees of freedom (plus spin-orbit interaction) are discussed in terms of a diabatic representation. The total angular momentum of the field-free system and the angular momentum transferred by absorption (or emission) of a photon are explicitly considered in the derivation of the coupled scattering equations. A model calculation is discussed for the Xe + F collision system.

Quantum mechanical theory of a structured atom–diatom collision system: A+BC(1Σ)

The problem of a 2P state atom colliding with a singlet sigma state diatom, which involves multiple potential surfaces, is investigated. Within a diabatic representation for the electronic degrees of freedom (plus spin–orbit interaction), coupled scattering equations are derived in both space‐fixed and body–fixed coordinate systems, and coefficients analogous to Percival–Seaton coefficients are exhibited. Approximations to the exact equations, including angular momenta decoupling approximations, are discussed for both the space‐fixed and body‐fixed formalisms.

Semiclassical theory of electronic transitions in molecular collisions: Combined effects of tunneling and energetically inaccessible electronic states

The semiclassical theory of collision‐induced electronic transitions is extended to describe tunneling and the effect of energetically inaccessible states. The powerful technique of analytic continuation is utilized to yield very good agreement with exact quantum mechanical results on some model systems. The inaccessible states have a significant effect on transmission coefficients and thus can be important in semiclassical studies of molecular reactions.

Adiabiatic ab initio potential curves for the B′ 1Σ+u state of H2

There is reported here an accurate ab initio calculation of the fixed nuclei potential curve for the B′ 1Σ+u state of H2 together with approximate values of the adiabatic corrections to the potential curve for this state. The state is observed to have two minima in its potential with the very small maxima occurring at approximately, R=5.5a0. Dipole transition moments and oscillator strengths for X 1Σ+g ↔ B 1Σ+u transitions are given for a wide range of internuclear separations.

An angular momentum approximation for molecular collisions in the presence of intense laser radiation

An approximation to a previously presented rigorous description of molecular (atom-atom) collisions occurring in the presence of intense radiation is investigated. This rigorous description explicitly considers the angular momentum transferred between the molecule and the radiation field in the absorption or emission of a photon, but involves a complicated system of close-coupled equations which must be solved independently for each projection M of the initial, total molecular angular momentum. (This is a direct consequence of the lack of rotational invariance in the molecule-field problem.) These equations are solved for a model system which mimics the collision of a halogen with a rare gas atom. Empirical observations made in the course of performing these calculations lead to the development of an approximation which avoids the repeated calculations for each initial M. This orientational average approximation greatly reduces the effort required to describe the system, and for the model calculation, yie...

Quantum mechanical study of electronic transitions in coplanar atom–diatom collisions: Quenching of fluorine by H2

A coplanar quantum mechanical study of rotational energy transfer in the quenching of the fluorine atom by H2 is carried out. While constrained to a fixed plane, the internal nuclear degrees of freedom of the system include rotation as well as vibration. The electronic degrees of freedom are represented by three interacting semiempirical potential energy surfaces. The study indicates that the primary factors in the relative ordering of the magnitudes of state‐selected cross lengths are the magnitude and sign of the energy defect, and the existence (or nonexistence) of nearby thresholds.

A new semiclassical decoupling scheme for electronic transitions in molecular collisions - Application to vibrational-to-electronic energy transfer

A new semiclassical decoupling scheme (the trajectory‐based decoupling scheme) is introduced in a computational study of vibrational‐to‐electronic energy transfer for a simple model system that simulates collinear atom–diatom collisions. The probability of energy transfer (P) is calculated quasiclassically using the new scheme as well as quantum mechanically as a function of the atomic electronic‐energy separation (λ), with overall good agreement between the two sets of results. Classical mechanics with the new decoupling scheme is found to be capable of predicting resonance behavior whereas an earlier decoupling scheme (the coordinate‐based decoupling scheme) failed. Interference effects are not exhibited in P vs λ results.

A new propagation method for the radial Schrödinger equation

Abstract A new method for propagating the solution of the radial Schrodinger equation is derived from a Taylor series expansion of the wavefunction and partial re-summation of the infinite series. Truncation of the series yields an approximation to the exact propagator which is applied to a model calculation and found to be highly convergent.

Electronic-to-rotational energy transfer in molecular collisions☆

Abstract A quantum mechanical study of collision induced electronic-to-rotational energy transfer in the fluorine—para-hydrogen system (F + H 2 ) is reported. The three potential energy surfaces of the system, constrained to lie in a fixed plane, are obtained by the diatomics-in-molecules approach, and close-coupling calculations are performed in a diabatic representation. An enhancement of rotationally inelastic (compared to rotationally elastic) transitions is observed when fluorine makes a transition from its upper to its lower spin—orbit state.

Quantum-mechanical calculation of three-dimensional atom-diatom collisions in the presence of intense laser radiation

A formalism is presented for describing the collision of fluorine with the hydrogen molecule in the presence of intense radiation. For a laser frequency on the order of the spin–orbit splitting of fluorine, the interaction of the molecular system with the radiation occurs at relatively long range where, for this system, the electric dipole is vanishingly small. Hence the interaction occurs due to the magnetic dipole coupling. Even so, at low collision energies a substantial enhancement of the quenching cross section is found for a radiation intensity of 1011 W/cm2.