The ionization potential (IP) of radium monofluoride (RaF) was measured to be 4.969(2)[10] eV, revealing a relativistic enhancement in the series of alkaline earth monofluorides. The results are in agreement with a relativistic coupled-cluster prediction of 4.981(7) eV, incorporating up to quantum electrodynamics corrections. Using the same computational methodology, an improved calculation for the dissociation energy (D_{0}) of 5.54(5) eV is presented. This confirms that RaF joins the group of diatomic molecules for which D_{0}>IP, paving the way for precision control and interrogation of its Rydberg states.

Silicates and silica are the major components of interstellar silicon-based dust grains and mainly composed of silicon and oxygen. Information about their geometric, electronic, optical, and photochemical properties is crucial for developing astrochemical models describing dust grain formation. To this end, we characterize herein the optical spectrum of mass-selected Si2O2 + cations in the 295-709 nm range using electronic photodissociation (EPD). The EPD spectra are recorded in a quadrupole/time-of-flight tandem mass spectrometer coupled to a laser vaporization source and compared to complementary time-dependent density functional theory (TD-DFT) calculations at the UB3LYP-D3/aug-cc-pVQZ level of theory, determining structures, energies, electronic spectra, and fragmentation energies of the low-energy isomers. The EPD spectrum is observed in the lowest-energy fragmentation channel, corresponding to SiO+ + SiO. The high calculated dissociation threshold of D 0 = 4.60 eV (37,102 cm-1) requires two-photon absorption for EPD. The three electronic transitions observed at 19,264, 25,667, and 32,216 cm-1 are attributed to transitions from the doublet ground state of the most stable rhombic structure of Si2O2 + (D 2h , 2B1u) into the first, fourth, and fifth excited doublet states, D1(2Ag), D4(2B2g), and D5(2B3u), respectively. The resolved vibronic structure of the D4 and D5 state is analyzed by Franck-Condon Herzberg-Teller (FCHT) simulations to suggest vibrational assignments. The calculations indicate the reduction of symmetry from D 2h to C 2v in the D4 state along the nu 4(b1u) coordinate (resulting in a flat double minimum potential), while the dipole-forbidden D5 state gains its vibronic intensity from HT coupling to the same nu 4 mode.

The radiative lifetime of the A (2)Pi(1/2) (v = 0) state in radium monofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state and the related decay rate Gamma = 2.86(8) . 86(8) x 107 7 s-1 - 1 are of relevance to the laser cooling of RaF via the optically closed A (2)Pi(1/2) <- X (2)Sigma(1/2) transition, which makes the molecule a promising probe to search for new physics. RaF is found to have a comparable photon-scattering rate to homoelectronic laser-coolable molecules. Owing to its highly diagonal Franck-Condon matrix, it is expected to scatter an order of magnitude more photons than other molecules when using just three cooling lasers, before it decays to a dark state. The lifetime measurement in RaF is benchmarked by measuring the lifetime of the 8P3/2 P 3 / 2 state in Fr to be 83(3) ns, in agreement with literature.

Molecules containing short-lived, radioactive nuclei are uniquely positioned to enable a wide range of scientific discoveries in the areas of fundamental symmetries, astrophysics, nuclear structure, and chemistry. Recent advances in the ability to create, cool, and control complex molecules down to the quantum level, along with recent and upcoming advances in radioactive species production at several facilities around the world, create a compelling opportunity to coordinate and combine these efforts to bring precision measurement and control to molecules containing extreme nuclei. In this manuscript, we review the scientific case for studying radioactive molecules, discuss recent atomic, molecular, nuclear, astrophysical, and chemical advances which provide the foundation for their study, describe the facilities where these species are and will be produced, and provide an outlook for the future of this nascent field.

The high resolution ro-vibrational spectrum of the diatomic molecule vanadium oxide (VO) in the gas phase was measured around 1000 cm-1. In total, 1529 ro-vibrational transitions were assigned, in a spectral range of 984-1036 cm-1. For many transitions, the hyperfine structure resulting from the nuclear spin of 51V were resolved and the molecular parameters for the first (v = 1) and second (v = 2) excited vibrational state of VO were derived. The molecules were generated using a laser ablation source in which a vanadium rod was laser ablated and gaseous nitrous oxide (N2O) was introduced, as an oxygen donor. Subsequent supersonic adiabatic expansion cooled the molecules. The spectrum of VO was measured with quantum cascade lasers where the laser beams were perpendicularly oriented to the supersonic jet.

The radiative lifetime of the AΠ1/22 (v=0) state in radium monofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state and the related decay rate Γ=2.86(8)×107 s−1 are of relevance to the laser cooling of RaF via the optically closed AΠ1/22←XΣ1/22 transition, which makes the molecule a promising probe to search for new physics. RaF is found to have a comparable photon-scattering rate to homoelectronic laser-coolable molecules. Owing to its highly diagonal Franck-Condon matrix, it is expected to scatter an order of magnitude more photons than other molecules when using just three cooling lasers, before it decays to a dark state. The lifetime measurement in RaF is benchmarked by measuring the lifetime of the 8P3/2 state in Fr to be 83(3) ns, in agreement with literature. Published by the American Physical Society 2024

Molecules containing heavy radioactive nuclei are predicted to be extremely sensitive to violations of the fundamental symmetries of nature. The nuclear octupole deformation of certain radium isotopes massively boosts the sensitivity of radium monofluoride molecules to symmetry-violating nuclear properties. Moreover, these molecules are predicted to be laser coolable. Here we report measurements of the rovibronic structure of radium monofluoride molecules, which allow the determination of their laser cooling scheme. We demonstrate an improvement in resolution of more than two orders of magnitude compared to the state of the art. Our developments allowed measurements of minuscule amounts of hot molecules, with only a few hundred per second produced in a particular rotational state. The combined precision and sensitivity achieved in this work offer opportunities for studies of radioactive molecules of interest in fundamental physics, chemistry and astrophysics. Measurements of the rovibronic structure of radium monofluoride molecules allow the identification of a laser cooling scheme. This will enable precise tests of fundamental physics, such as searches for parity or time-reversal symmetry violation.

The radiative lifetime of the A ^2 Π_1/2 (v=0) state in radium monofluoride (RaF) is measured to be 35(1) ns. The lifetime of this state is of relevance to the laser cooling of RaF via the optically closed A ^2 Π_1/2← X ^2Σ_1/2 transition, which is an advantageous aspect of the molecule for its promise as a probe for new physics. The radiative decay rate Γ = 2.9(2)× 10^7 s^-1 is extracted using the lifetime, which determines the natural linewidth of 4.6(3) MHz and the maximum photon scattering rate of 4.1(3)× 10^6 s^-1 of the laser-cooling transition. RaF is thus found to have a comparable photon-scattering rate with other laser-cooled molecules, while thanks to its highly diagonal Franck-Condon matrix it is expected to scatter an order of magnitude more photons when using 3 cooling lasers before it decays to a dark state. The lifetime measurement in RaF is benchmarked by measuring the lifetime of the 8P_3/2 state in Fr to be 83(3) ns, in agreement with literature.

We demonstrate that the isotope shift in isotopomers of diatomic molecules, where the nucleus of one of its constituent atoms is replaced by another isotope, can be expressed as the sum of a field shift and a mass shift, similar to the atomic case. We show that a linear relation holds between atomic and molecular isotopes shifts, thus extending the King-plot analysis to molecular isotope shifts. Optical isotope shifts in YbF and ZrO and infrared isotope shifts in SnH are analyzed with a molecular King-plot approach, utilizing Yb$^{+}$ and Zr$^{+}$ ionic isotope shifts and charge radii of Sn obtained with non-optical methods. The changes in the mean-squared nuclear charge radii $\delta \langle r^2 \rangle$ of $^{170-174,176}$Yb and $^{90-92,94,96}$Zr extracted from the molecular transitions are found to be in excellent agreement with the values from the spectroscopy of Yb$^{+}$ and Zr$^{+}$, respectively. On the contrary, in the case of the vibrational-rotational transition in SnH, no sensitivity to the nuclear volume could be deduced within the experimental resolution, which makes it unsuitable for the extraction of nuclear charge radii but provides insights into the molecular electronic wave function not accessible via other methods. The new opportunities offered by the molecular King-plot analysis for research in nuclear structure and molecular physics are discussed.

We report the spectroscopy of the 14 lowest excited electronic states in the radioactive molecule radium monofluoride (RaF). The observed excitation energies are compared with fully relativistic state-of-the-art Fock-space coupled cluster (FS-RCC) calculations, which achieve an agreement of >=99.64% (within ~12 meV) with experiment for all states. Guided by theory, a firm assignment of the angular momentum and term symbol is made for 10 states and a tentative assignment for 4 states. The role of high-order electron correlation and quantum electrodynamics effects in the excitation energy of excited states is studied, found to be important for all states. Establishing the simultaneous accuracy and precision of calculations is an important step for research at the intersection of particle, nuclear, and chemical physics, including searches of physics beyond the Standard Model, for which RaF is a promising probe.

High-resolution absorption, dispersed fluorescence emission, and photoionization cross sections are presented for gas-phase adamantane excited by synchrotron radiation in the exciting-photon energy range of 6–30 eV. Relative and absolute absorption cross sections of so-far unmatched resolution of down to 0.27 cm−1 line width in the region from 6.4–28 eV are shown along with newly discovered vibronic substructures around the HOMO–LUMO transition. Absorption line positions are provided with very high accuracy and listed in tabular form to be used as spectral fingerprints for the detection of adamantane in interstellar media, where its column density may be determined via the absolute cross sections. The fluorescence emission lies in the ultraviolet range from 190–250 nm and is excited starting at the HOMO–LUMO transition at 6.49 eV, which corresponds to the highest fluorescence emission energy. Hitherto unreported fluorescence in the same spectral range and relative photoionization cross sections in the exciting-photon energy range up to 30 eV are also presented along with lifetime measurements for differentiation of the involved electronic states.

Dialuminum monoxide, Al2O, has been investigated in the laboratory at mid-IR wavelengths around 10 μm at high spectral resolution. The molecule was produced by laser ablation of an aluminum target with the addition of gaseous nitrous oxide, N2O. Subsequent adiabatic cooling of the gas in a supersonic beam expansion led to rotationally cold spectra. In total, 848 ro-vibrational transitions have been assigned to the fundamental asymmetric stretching mode ν3 and to five of its hot bands, originating from excited levels of the ν1 symmetric stretching mode and the ν2 bending mode. The measurements encompass 11 vibrational energy states (v1 v2l v3). The ro-vibrational transitions show spin statistical line intensity alternation of 7:5, which is caused by two identical aluminum nuclei of spin I = 5/2 at both ends of the centrosymmetric molecule of structure Al-O-Al. The less effective cooling of vibrational states in the supersonic beam expansion allowed measurement of transitions in excited vibrational states at energies of 1000 cm-1 and higher, while rotational levels within vibrational modes exhibited thermal population, with rotational temperatures around Trot = 115 K. Molecular parameters for 11 vibrational states were derived, including rotation and centrifugal distortion constants and l-type doubling constants for the states (v1 v2l v3) = (0 11 0) and (0 11 1) and an l-type resonance between the states (0 20 0) - (0 22 0) and (0 20 1) - (0 22 1). From the experimental results, rotational correction terms and the equilibrium bond length re were derived. The measurements were supported and guided by high-level quantum-chemical calculations that agree well with the derived experimental results.

Recently, a breakthrough has been achieved in laser-spectroscopic studies of short-lived radioactive compounds with the first measurements of the radium monofluoride molecule (RaF) UV/vis spectra. We report results from high-accuracy ab initio calculations of the RaF electronic structure for ground and low-lying excited electronic states. Two different methods agree excellently with experimental excitation energies from the electronic ground state to the 2Π1/2 and 2Π3/2 states, but lead consistently and unambiguously to deviations from experimental-based adiabatic transition energy estimates for the 2Σ1/2 excited electronic state, and show that more measurements are needed to clarify spectroscopic assignment of the 2Δ state.

Radium compounds have attracted recently considerable attention due to both development of ex-perimental techniques for high-precision laser spectroscopy of molecules with short-lived nuclei and amenability of certain radium compounds for direct cooling with lasers. Currently, radium monofluo-ride (RaF) is one of the most studied molecules among the radium compounds, both theoretically and recently also experimentally. Complementary studies of further diatomic radium derivatives are highly desired to assess the influence of chemical substitution on diverse molecular parameters, especially on those connected with laser cooling, such as vibronic transition probabilities, and those related to viola-tions of fundamental symmetries. In this article high-precision ab initio studies of electronic and vibronic levels of diatomic radium monochloride (RaCl) are presented. Recently developed approaches for treating electronic correlation with Fock-space coupled cluster methods are applied for this purpose. Theoretical results are compared to an early experimental investigation by Lagerqvist and used to partially reassign the experimentally observed transitions and molecular electronic levels of RaCl. Effective constants of P-odd hyperfine interaction Wa and P, T-odd scalar-pseudoscalar nucleus-electron interaction Ws in the ground electronic state of RaCl are estimated within the framework of a quasirelativistic Zeroth-Order Regular Approximation approach and compared to parameters in RaF and RaOH. (c) 2021 Elsevier Ltd. All rights reserved.

In this study, we present the ro-vibrationally resolved gas-phase spectrum of the diatomic molecule TiO around 1000 cm(-1). Molecules were produced in a laser ablation source by vaporizing a pure titanium sample in the atmosphere of gaseous nitrous oxide. Adiabatically expanded gas, containing TiO, formed a supersonic jet and was probed perpendicularly to its propagation by infrared radiation from quantum cascade lasers. Fundamental bands of 46-50TiO and vibrational hotbands of (TiO)-Ti-48 are identified and analyzed. In a mass-independent fitting procedure combining the new infrared data with pure rotational and electronic transitions from the literature, a Dunham-like parameterization is obtained. From the present data set, the multi-isotopic analysis allows to determine the spin-rotation coupling constant c and the BornOppenheimer correction coefficient DTiU10 for the first time. The parameter set enables to calculate the BornOppenheimer correction coefficients Delta(Ti)(U02) and Delta(O)(U02). In addition, the vibrational transition moments for the observed vibrational transitions are reported. (C) 2021 Elsevier Inc. All rights reserved.

Molecular spectroscopy offers opportunities for the exploration of the fundamental laws of nature and the search for new particle physics beyond the standard model 1 – 4 . Radioactive molecules—in which one or more of the atoms possesses a radioactive nucleus—can contain heavy and deformed nuclei, offering high sensitivity for investigating parity- and time-reversal-violation effects 5 , 6 . Radium monofluoride, RaF, is of particular interest because it is predicted to have an electronic structure appropriate for laser cooling 6 , thus paving the way for its use in high-precision spectroscopic studies. Furthermore, the effects of symmetry-violating nuclear moments are strongly enhanced 5 , 7 – 9 in molecules containing octupole-deformed radium isotopes 10 , 11 . However, the study of RaF has been impeded by the lack of stable isotopes of radium. Here we present an experimental approach to studying short-lived radioactive molecules, which allows us to measure molecules with lifetimes of just tens of milliseconds. Energetically low-lying electronic states were measured for different isotopically pure RaF molecules using collinear resonance ionisation at the ISOLDE ion-beam facility at CERN. Our results provide evidence of the existence of a suitable laser-cooling scheme for these molecules and represent a key step towards high-precision studies in these systems. Our findings will enable further studies of short-lived radioactive molecules for fundamental physics research.

We present pure rotational transitions of the rare iron monoxide isotopologues.,andin their lowest spin states. For, the rotational spectrum reveals hyperfine splitting due to the nuclear spin of. We use Dunham-like parameters to analyse the new laboratory data together with data from the literature. In particular, we are able to derive the Born-Oppenheimer breakdown parametersandand the corresponding equilibrium bond length of. With these new accurate molecular parameters line positions on a sub-MHz accuracy level can be calculated, including those of the radioactive isotopologue. The new data allow for an astronomical search for the rareisotopologues using sensitive radio telescopes, like the Atacama Large Millimetre/submillimetre Array. [GRAPHICS] .

A variety of standard techniques exist for estimating molecular bond lengths from spectroscopic data of the vibrational ground state. In typical order of increasing accuracy these different estimates are known as r0, rs, and rm. However, for the C3 molecule each of these spectroscopically determined values is very different from that obtained in a recent high-quality ab initio calculation. We ascribe this difference to the large-amplitude ν2 bending vibration of C3. By recognizing that vibrational averaging means that the molecule is effectively bent, even in the ground vibrational state, we develop a simple new method for estimating the bond length. This involves approximating the rotational parameter along the axis that becomes the molecular axis at linearity as A0=ν22. This value is then used in the evaluation of rm, rather than assuming the molecule is linear. We test this approximation for A0 and also show that the C–C bond length we obtain is in better agreement, by an order of magnitude, with the ab initio value than any of the standard linear approaches.