Radiative rotational lifetimes and state-resolved relative detachment cross sections from photodetachment thermometry of molecular anions in a cryogenic storage ring

TL;DR

This study uses cryogenic storage ring photodetachment spectroscopy to measure radiative lifetimes, rotational state populations, and transition dipole moments of OH$^-$ ions, providing precise molecular data at very low temperatures.

Contribution

It presents the first detailed measurements of radiative lifetimes and state-resolved cross sections of molecular anions in a cryogenic environment, advancing molecular spectroscopy techniques.

Findings

Effective radiative temperature near 15 K

90% of ions in rotational ground state

Measured J=1 lifetime of about 193 seconds

Abstract

Photodetachment thermometry on a beam of OH$^-$ in a cryogenic storage ring cooled to below 10 K is carried out using two-dimensional, frequency and time dependent photodetachment spectroscopy over 20 minutes of ion storage. In equilibrium with the low-level blackbody field, we find an effective radiative temperature near 15 K with about 90% of all ions in the rotational ground state. We measure the J = 1 natural lifetime (about 193 s) and determine the OH$^-$ rotational transition dipole moment with 1.5% uncertainty. We also measure rotationally dependent relative near-threshold photodetachment cross sections for photodetachment thermometry.