Laser Spectroscopy of Aromatic Molecules with Optical Cycling Centers: Strontium(I) Phenoxides

Abstract

We report the production and spectroscopic characterization of strontium­(I) phenoxide (SrOC6H5 or SrOPh) and variants featuring electron-withdrawing groups designed to suppress vibrational excitation during spontaneous emission from the electronically excited state. Optical cycling closure of these species, which is the decoupling of the vibrational state changes from spontaneous optical decay, is found by dispersed laser-induced fluorescence spectroscopy to be high, in accordance with theoretical predictions. A high-resolution, rotationally resolved laser excitation spectrum is recorded for SrOPh, allowing the estimation of spectroscopic constants and identification of candidate optical cycling transitions for future work. The results confirm the promise of strontium phenoxides for laser cooling and quantum state detection at the single-molecule level.

Extending the Large Molecule Limit: The Role of Fermi Resonance in Developing a Quantum Functional Group

“…To investigate the influence of metal atom on anharmonic vibrational coupling, we also studied two strontium phenoxides, SrOPh and SrOPh-3,4,5-F 3 . Previous study 17 has provided low-resolution DLIF spectra for these molecules. Figures 4a and 4b displays the higher resolution DLIF spectra recorded here for SrOPh from the excited A ̃and B ̃states.…”

“…Functionalizing large molecules with optical cycling centers (OCCs) is being explored as a means for extending the exquisite control available in quantum information science to the chemical domain. − Success requires that these OCCs absorb and emit many photons without changing their vibrational states. To accomplish this task, molecular design rules are being developed, aided and validated by experiments, to guide the creation of the ideal quantum functional groups. − For example, prior work has demonstrated that alkaline earth alkoxides provide a general and versatile chemical moiety for optical cycling applications, as the alkaline earth radical electron can be excited without perturbing the vibrational structure of the molecule. ,,− Similarly, traditional physical organic principles, such as electron-withdrawing, have been shown to improve OCCs performance. , Further, experimental and theoretical extensions to more complex acenes, , diamondoids, and even surfaces suggest an exciting path forward for creating increasingly complex and functional quantum systems.…”

“…A series of calcium and strontium phenoxides (CaOPh, CaOPh-3-F, CaOPh-4-F, CaOPh-3,4,5-F 3 , SrOPh, and SrOPh-3,4,5-F 3 , Ph = phenyl group, Figure a) were produced via laser ablation of the alkaline earth metal into a mixture of the precursor ligand and Ne buffer gas inside a cryogenic cell operated at a temperature of ∼20 K (Figure S1). As sketched in Figures b and c, the vibrational structure of these molecules was probed with two types of measurements: dispersed laser-induced fluorescence (DLIF) spectroscopy, which probes the vibrational structure in the electronic ground state ( X̃ ), and excitation spectroscopy, which examines the vibrational structure in the excited states ( à and B̃ ). In DLIF spectroscopy (Figure b), vibrationally cold molecules are excited to the ground vibrational level of the electronically excited à and B̃ states, à / B̃ ( v ′ = 0) ← X̃ ( v ″ = 0), and the resulting fluorescence is recorded as a function of wavelength.…”

Intensity-Borrowing Mechanisms Pertinent to Laser Cooling of Linear Polyatomic Molecules

“…Therefore, the identification of promising laser-coolable molecules using both high-resolution spectroscopy and quantum-chemical calculations plays a key role in the laser cooling of molecules. The experimental measurements of vibronic branching ratios using high-resolution laser spectroscopy ,− have recently been combined with optical cycling to further enhance the sensitivity of the measurement . Theoretical and computational tools are also being developed, aiming to provide useful information about optical cycling transitions.…”

Zwitterions Functionalized by Optical Cycling Centers: Toward Laser-Coolable Polyatomic Molecular Cations

“…It is interesting that compound 2 can also be constructed as a derivative from the neutral Sr + -phenoxide complex, as extensively discussed in ref , through “cationization” of the neutral OCC-containing complex by adding the positively charged trimethyl­ammonium group N + (CH 3 ) 3 . Though both views are formally equivalent, it is worth noting that the lowest-energy dissociation channel of the complex corresponds to the dissociation into Sr + and the zwitterion.…”