Fine- and hyperfine-structure effects in molecular photoionization: II. Resonance-enhanced multiphoton ionization and hyperfine-selective generation of molecular cations

TL;DR

This paper develops a theoretical model to describe hyperfine-structure effects in resonance-enhanced multiphoton ionization (REMPI), enabling better analysis and hyperfine-selective production of molecular ions for spectroscopy.

Contribution

It generalizes previous models to include hyperfine effects in both the neutral excitation and ionization steps of REMPI processes.

Findings

Model predicts hyperfine populations in molecular ions produced by REMPI.

Provides a theoretical framework for hyperfine-selective ionization experiments.

Facilitates analysis of experimental results involving hyperfine structures.

Abstract

Resonance-enhanced multiphoton ionization (REMPI) is a widely used technique for studying molecular photoionization and producing molecular cations for spectroscopy and dynamics studies. Here, we present a model for describing hyperfine-structure effects in the REMPI process and for predicting hyperfine populations in molecular ions produced by this method. This model is a generalization of our model for fine- and hyperfine- structure effects in one-photon ionization of molecules presented in the preceding companion article. This generalization is achieved by covering two main aspects: (1) treatment of the neutral bound-bound transition including hyperfine structure that makes up the first step of the REMPI process and (2) modification of our ionization model to account for anisotropic populations resulting from this first excitation step. Our findings may be used for analyzing results from experiments with molecular ions produced by REMPI and may serve as a theoretical background for hyperfine-selective ionization experiments.