# Triplet Rydberg States of Aluminum Monofluoride

## TL;DR

This paper identifies and characterizes previously unobserved electronic states in aluminum monofluoride, important for laser cooling and trapping experiments.

## Contribution

The study experimentally confirms the predicted energy ordering of triplet states in AlF and reveals new insights into their interactions.

## Key findings

- The d3Π (v = 0–6) and e3Δ (v = 0–2) states of AlF were characterized and confirmed.
- Spin–orbit and spin–rotation interactions between d3Π and e3Δ states explain unexpected rotational structures.
- The ionization potential of AlF was determined as 78,492(1) cm–1 from the d3Π state.

## Abstract

Aluminum monofluoride
(AlF) is a suitable molecule for laser cooling
and trapping. Such experiments require extensive spectroscopic characterization
of the electronic structure. Two of the theoretically predicted higher-lying
triplet states of AlF, the counterparts of the well-characterized
D1Δ and E1Π states, had not been
experimentally identified yet. We here report on the characterization
of the d3Π (v = 0–6) and
e3Δ (v = 0–2) states, confirming
the predicted energetic ordering of these states (J. Chem.
Phys.1988,88, 5715–5725),
as well as of the f3Σ+ (v = 0–2) state. The transition intensity of the d3Π, v = 3 – a3Π, v = 3 band is negligibly small. This band gets its weak,
unexpected rotational structure via intensity borrowing from the nearby
e3Δ, v = 2 – a3Π, v = 3 band, made possible via spin–orbit
and spin–rotation interaction between the d3Π
and e3Δ states. This interaction affects the equilibrium
rotational constants in both states; their deperturbed values yield
equilibrium internuclear distances that are consistent with the observations.
We determined the ionization potential of AlF to be 78,492(1) cm–1 by ionization from the d3Π state.