# Visible and Ultraviolet Laser Spectroscopy of ThF

## TL;DR

This study conducts broadband laser spectroscopy on ThF to identify states suitable for efficient ion production in the eEDM search, reporting new vibronic bands and proposing methods to enhance ionization efficiency.

## Contribution

It reports the first extensive survey of ThF vibronic states, identifies an intermediate state for efficient ThF$^+$ ion production, and proposes a vibrational autoionization method to reach near 100% efficiency.

## Key findings

- 345 new vibronic bands of ThF identified
- 30% ion production efficiency achieved with specific intermediate state
- Proposed method to increase efficiency to ~100% using vibrational autoionization

## Abstract

The molecular ion ThF$^+$ is the species to be used in the next generation of search for the electron's Electric Dipole Moment (eEDM) at JILA. The measurement requires creating molecular ions in the eEDM sensitive state, the rovibronic ground state $^3\Delta_1$, $v^+=0$, $J^+=1$. Survey spectroscopy of neutral ThF is required to identify an appropriate intermediate state for a Resonance Enhanced Multi-Photon Ionization (REMPI) scheme that will create ions in the required state. We perform broadband survey spectroscopy (from 13000 to 44000~cm$^{-1}$) of ThF using both Laser Induced Fluorescence (LIF) and $1+1'$ REMPI spectroscopy. We observe and assign 345 previously unreported vibronic bands of ThF. We demonstrate 30\% efficiency in the production of ThF$^+$ ions in the eEDM sensitive state using the $\Omega = 3/2$ [32.85] intermediate state. In addition, we propose a method to increase the aforementioned efficiency to $\sim$100\% by using vibrational autoionization via core-nonpenetrating Rydberg states, and discuss theoretical and experimental challenges. Finally, we also report 83 vibronic bands of an impurity species, ThO.