Properties of nearly one-electron molecules. II. Application to the Rydberg spectrum of CaF

Abstract

The ab initio K matrix method described in the preceding paper (Part I) is applied to the Rydberg electronic structure of calcium monofluoride. The spectroscopic quantum defects for the 2Sigma+, 2Pi, 2Delta, and 2Phi states of CaF are computed using the effective potential of Arif et al. [M. Arif, Ch. Jungen, and A. L. Roche, J. Chem. Phys. 106, 4102 (1997)]. Satisfactory agreement with the experimental values is obtained. The eigenquantum defects obtained from the reaction matrix for the CaF++e- system are found to be strongly energy dependent. The analysis shows that the main features of the energy-dependent structure in the eigenphases are a consequence of a broad molecular shape resonance. Partial-l (orbital angular momentum) characters of two interacting collision eigenchannels vary rapidly as a function of increasing collision energy. This prominent variation leads to interference structure in the intensities for transitions into the ionization continuum, manifesting nodal points in the total ionization cross section in the continuum above the shape resonance. The usefulness of this structure in the ionization cross section as a direct probe of the l-character of the bound state is discussed. In addition, ab initio results for the photoelectron angular distribution and the anisotropy parameter are presented. These computed results are susceptible to direct experimental verification.

A quantum defect model for the s, p, d, and f Rydberg series of CaF

“…26,45,46 The R-matrix approach 47 partitions the computational solution of the Schrödinger equation for the electron/ion system into a dynamically complex region near the ion-core and a long-range region of simpler dynamics. 26,45,46 The R-matrix approach 47 partitions the computational solution of the Schrödinger equation for the electron/ion system into a dynamically complex region near the ion-core and a long-range region of simpler dynamics.…”

Electric potential invariants and ions-in-molecules effective potentials for molecular Rydberg states

“…In this paper, we focus on optimizing effective potentials for use in Rydberg R-matrix calculations, 17,104,119 as a faithful representation of charge/molecular-ion interactions, and as a predictive tool for moments and polarizabilities. We have shown in Figure 1 how the origin chosen for a single-center multipole series affects the convergence properties of a multipole series, and the transition from penetrating to non-penetrating in the representation of Rydberg states.…”

“…The (0)-superscripted multipoles Q (0) L in (17) are the multipole moments of the ion core, determined in the absence of an external potential or test charge. The energy with angular dependence L is expressed in terms of Q (0) L and Q (S) L , separating static multipoles from polarization.…”

“…In a ground-breaking 1997 paper, Arif, Jungen, and Roche 14 proposed a one-electron effective potential for polar diatomic Rydberg states and applied it to Rydberg states of CaF and BaF, both of which are effective one-electron systems. This AJR potential has been applied in MQDT calculations for rare-gas hydrides, 53,54 CaCl, 15 BaI, 16 and CaF, 17,104 allowing comparison to quantum-defect matrices derived from Rydberg experimental data. 19 The AJR potential, excluding core de-shielding terms, uses Coulomb, atomic polarization, and dipole energy terms in a way that is equivalent to the following expression:…”

“…In this paper, we start from a distributed-polarizability two-center effective potential for polar molecules known as the Applequist-Silberstein 12 or dipole-induced-dipole (DID) model and make connections to ab initio calculations and single-center multipolar perturbation theory. The single-center multipole and polarizability expansion, pioneered by Buckingham, 13 is a convenient meeting place between approaches that include ab initio calculations, multi-center effective potentials, multi-channel quantum defect theory (MQDT) calculations using an effective potential, [14][15][16][17] and quantum defects fitted to experimental data. 18,19 This combination of approaches extends previous work by making a connection between atomic and molecular properties, by comparing predictions of effective potentials using different models of mutual polarization between atomic centers, and by making it possible to use a phenomenological effective potential to predict multipole moments and polarizabilities.…”