Spectroscopic investigations of ThF and ThF+

Abstract

The electronic spectra of ThF and ThF(+) have been examined using laser induced fluorescence and resonant two-photon ionization techniques. The results from high-level ab initio calculations have been used to guide the assignment of these data. Spectra for ThF show that the molecule has an X (2)Δ(3/2) ground state. The upper spin-orbit component, X (2)Δ(5/2) was found at an energy of 2575(15) cm(-1). The low-lying states of ThF(+) were probed using dispersed fluorescence and pulsed field ionization-zero kinetic energy (PFI-ZEKE) photoelectron spectroscopy. Vibronic progressions belonging to four electronic states were identified. The lowest energy states were clearly (1)Σ(+) and (3)Δ(1). Although the energy ordering could not be rigorously determined, the evidence favors assignment of (1)Σ(+) as the ground state. The (3)Δ(1) state, of interest for investigation of the electron electric dipole moment, is just 315.0(5) cm(-1) above the ground state. The PFI-ZEKE measurements for ThF yielded an ionization energy of 51 581(3) cm(-1). Molecular constants show that the vibrational constant increases and the bond length shortens on ionization. This is consistent with removal of a non-bonding Th-centered 6d or 7s electron. Laser excitation of ThF(+) was used to probe electronically excited states in the range of 19,000-21,500 cm(-1).

Broadband velocity modulation spectroscopy of ThF+ for use in a measurement of the electron electric dipole moment

“…Vibrational assignments are determined by comparing observed band intensities to Franck-Condon factors and a thermal vibrational distribution. With prior knowledge of vibrational constants from Barker et al [17], and our measured B values, Franck-Condon factors were calculated and compared to observed intensities for the initial bands measured. With the rotational and vibrational constants we have observed in ThF + , the vibrational (0, 0) is always the strongest band.…”

“…The JILA experiment is currently using trapped HfF + [13], but ThF + is a promising candidate molecule for a future generation experiment due to its larger effective electric field [14,15,16] and longer-lived 3 ∆ 1 state. Assigning the ground state of ThF + has been experimentally challenging due to the proximity of both 1 Σ + and 3 ∆ states [17,18]. Calculations suggested that 3 ∆ 1 might be the ground state but uncertainties prevented a conclusive determination [19,15].…”

“…With this system we have scanned the entire wavelength range of 696 -900 nm, acquiring 3,260 cm −1 of continuous spectra at 150 MHz (0.005 cm −1 ) step-size. Additionally, guided by the results of the comb-vms and the PFI-ZEKE spectra from Barker et al [17], we have performed targeted cw-laser vms scans to identify additional experimentally useful transitions and to assign electronic-state Ω values via observation of low-J rotational lines. In total, we have fit 27 rovibronic transitions in ThF + and 5 transitions in a different thoriated molecular ion, potentially ThO + .…”

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

“…However for this species, the ab initio calculations are even more challenging, leading to larger theoretical uncertainties. The first spectroscopy of ThF + using PFI-ZEKE plus some LIF (unassigned) has recently been published [13], but, as was the case with HfF + , the higher excited states remain uncharacterized. By using highly non-linear fiber to broaden the comb spectrum [63] and a high repetition rate Ti:sapphire amplifier [64], we hope to cover over 2000 cm −1 with comb-vms.…”

“…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.…”