Bound and resonance states of the dipolar anion of hydrogen cyanide: competition between threshold effects and rotation in an open quantum system

TL;DR

This paper investigates the bound and resonance states of the dipolar anion of hydrogen cyanide using advanced quantum methods, revealing how electronic and rotational couplings influence state characteristics and decay widths.

Contribution

It introduces a novel algorithm for identifying resonant states in the complex energy plane and analyzes the transition from strong to weak electronic-rotational coupling regimes.

Findings

Electronic motion couples strongly to molecular rotation in bound states.

Resonance widths depend mainly on electron orbital angular momentum.

Transition from strong to weak coupling affects electron and molecular rotation dynamics.

Abstract

Bound and resonance states of the dipole-bound anion of hydrogen cyanide HCN$^-$ are studied using a non-adiabatic pseudopotential method and the Berggren expansion technique involving bound states, decaying resonant states, and non-resonant scattering continuum. We devise an algorithm to identify the resonant states in the complex energy plane. To characterize spatial distributions of electronic wave functions, we introduce the body-fixed density and use it to assign families of resonant states into collective rotational bands. We find that the non-adiabatic coupling of electronic motion to molecular rotation results in a transition from the strong-coupling to weak-coupling regime. In the strong coupling limit, the electron moving in a subthreshold, spatially extended halo state follows the rotational motion of the molecule. Above the ionization threshold, electron's motion in a resonance state becomes largely decoupled from molecular rotation. Widths of resonance-band members depend primarily on the electron orbital angular momentum.