B. R. Johnson

Bio: B. R. Johnson is an academic researcher. The author has contributed to research in topics: Hydrogen bond & Eigenfunction. The author has an hindex of 1, co-authored 1 publications receiving 364 citations.

The renormalized Numerov method applied to calculating bound states of the coupled‐channel Schroedinger equation

Abstract: The renormalized Numerov method, which was recently developed and applied to the one‐dimensional bound state problem [B. R. Johnson, J. Chem. Phys. 67, 4086 (1977)], has been generalized to compute bound states of the coupled‐channel Schroedinger equation. Included in this presentation is a generalization of the concept of a wavefunction node and a method for detecting these nodes. By utilizing node count information it is possible to converge to any specific eigenvalue without the need of an initial close guess and also to calculate degenerate eigenvalues and determine their degree of degeneracy. A useful interpolation formula for calculating the eigenfunctions at nongrid points is also given. Results of example calculations are presented and discussed. One of the example problems is the single center expansion calculation of the 1sσg and 2sσg states of H+2.

An improved log derivative method for inelastic scattering

Abstract: A new method for solving the close coupled equations of inelastic scattering is presented. The method is based on Johnson’s log derivative algorithm, and uses the same quadrature for the solution of the corresponding integral equations. However it differs from the original method in the use of a piecewise constant diagonal reference potential. This results in a reduction in matrix operations at subsequent energies, and an improved convergence of the solution with respect to the number of grid points. These advantages are clearly demonstrated when our method is applied to an atom–diatom rotational excitation problem.

Vibrational dependence of the anisotropic intermolecular potential of Ar–HF

Abstract: A new intermolecular potential for Ar–HF is obtained by fitting to results from high‐resolution microwave, far‐infrared, and infrared spectroscopy. The new potential, designated H6(4,3,2), is a function of the diatom mass‐reduced vibrational quantum number η=(v+ (1)/(2) )/(μHX)1/2 as well as the intermolecular distance R and angle θ, and has 22 adjustable parameters. It reproduces all the available spectroscopic data for levels of Ar–HF correlating with HF, v=0, 1, and 2, and DF, v=0 and 1. The H6(4,3,2) potential is qualitatively similar to previous potentials, with a linear Ar–H–F equilibrium geometry and a secondary minimum at the linear Ar–F–H geometry. Compared to the potential of Nesbitt et al. [J. Chem. Phys. 90, 4855 (1989)], obtained from spectra of Ar–HF (v=1), the H6(4,3,2) potential is rather deeper near the equilibrium geometry (Ar–H–F), but shallower around the secondary minimum (Ar–F–H). The absolute well depth increases by 19 cm−1 between HF v=0 and v=1. The vibrationally averaged inductio...

Cold hybrid ion-atom systems

Abstract: Hybrid systems of laser-cooled trapped ions and ultracold atoms combined in a single experimental setup have recently emerged as a new platform for fundamental research in quantum physics. This paper reviews the theoretical and experimental progress in research on cold hybrid ion-atom systems which aim to combine the best features of the two well-established fields. A broad overview is provided of the theoretical description of ion-atom mixtures and their applications, and a report is given on advances in experiments with ions trapped in Paul or dipole traps overlapped with a cloud of cold atoms, and with ions directly produced in a Bose-Einstein condensate. This review begins with microscopic models describing the electronic structure, interactions, and collisional physics of ion-atom systems at low and ultralow temperatures, including radiative and nonradiative charge-transfer processes and their control with magnetically tunable Feshbach resonances. Then the relevant experimental techniques and the intrinsic properties of hybrid systems are described. In particular, the impact is discussed of the micromotion of ions in Paul traps on ion-atom hybrid systems. Next, a review of recent proposals is given for using ions immersed in ultracold gases for studying cold collisions, chemistry, many-body physics, quantum simulation, and quantum computation and their experimental realizations. The last part focuses on the formation of molecular ions via spontaneous radiative association, photoassociation, magnetoassociation, and sympathetic cooling. Applications and prospects are discussed of cold molecular ions for cold controlled chemistry and precision spectroscopy.

Nonadiabatic representations of the 1Σ+u and 1Πu states of the N2 molecule

Abstract: The vibronic bands in the dipole‐allowed absorption spectrum of N2 associated with the lowest three electronic 1Σ+u and the lowest three electronic 1Πu states are represented in a basis of electronically coupled diabatic states as well as in the basis of nuclear‐momentum coupled adiabatic states. Parameters defining the diabatic states and their electronic coupling energies are first evaluated by fitting the eigenvalues of a vibronic interaction matrix to the observations. The coupled‐oscillator equations are then solved directly by Johnson’s numerical integration method and the diabatic representation is redetermined via the matrix method and coupled equations iteratively. The fit of the experimental vibronic terms, B values, and absorption intensities achieved with R‐independent electronic coupling energies in a diabatic basis of valence and Rydberg‐type states (b′+c′+e′)1Σ+u and (b+c+o)1Πu is satisfactory. Comparison with the corresponding adiabatic representation shows that the nonadiabatic perturbati...