Communication: Spectroscopic measurements for HfF+ of relevance to the investigation of fundamental constants

Abstract

The properties of the HfF+ cation are thought to be well-suited for investigations of the electron electric dipole moment (eEDM) and temporal variations of the fine structure constant. Precision spectroscopic measurements involving the X1Σ+ and low-lying 3Δ1 states have been proposed to measure both. Due to the lack of data for HfF+, the design of these experiments has relied entirely on the predictions of electronic structure calculations. Spectroscopic characterizations of the X1Σ+, 3Δ1, 3Δ2 and 3Δ3 states are reported. The results further support the contention that HfF+ is a viable candidate for eEDM measurements. The spacings between adjacent X1Σ+ and 3Δ1 levels are found to be less favorable for the proposed studies of the fine structure constant.

State-specific detection of trapped HfF+ by photodissociation

“…Any repulsive potentials must lie above the bond dissociation energy 51,200(1,600) cm −1 , which we determine by combining the measured neutral HfF bond dissociation energy [20] with the ionization energies of HfF [21] and Hf [22]. This estimate is in good agreement with that calculated from ab-initio theory [23].…”

“…, and [21,26]. We further verify the assignments of X 1 Σ + (v = 0) and 3 ∆ 1 (v = 0) by performing depletion spectroscopy with a continuous-wave laser tuned to resonance with a particular transition.…”

Broadband velocity modulation spectroscopy of HfF+: Towards a measurement of the electron electric dipole moment

“…This information, combined with data from [12], isotope shifts, and Λ-doubling structure provided the assignments in Table 1. Due to possible ambiguities, several bands are still unassigned as indicated.…”

“…Quoted uncertainties are 95% and are statistical, i.e., they do not account for any deviation from the Morse potential. δT e = T 180 e − T 178 e is an electronic isotope shift relative to 1 [12] with the old theoretical calculations of Petrov et al [19] and the improved theory discussed here. The theoretical values of B e from [19] were computed from the equilibrium bond length.…”

“…The energies of the lowlying 3 ∆ 1 , 3 ∆ 2 , and 3 ∆ 3 states were recently measured using pulsed-field ionization zero kinetic energy (PFI-ZEKE) spectroscopy [12,13]. Additionally, several isoelectronic species including TiO [14,15,16], TiF + and TiCl + [17,18] have been The eEDM experiment will utilize the J = 1 level of the 3 ∆ 1 metastable state.…”