Molecular spectroscopy offers opportunities for the exploration of the fundamental laws of nature and the search for new particle physics beyond the standard model1–4. 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 effects5,6. Radium monofluoride, RaF, is of particular interest because it is predicted to have an electronic structure appropriate for laser cooling6, thus paving the way for its use in high-precision spectroscopic studies. Furthermore, the effects of symmetry-violating nuclear moments are strongly enhanced5,7–9 in molecules containing octupole-deformed radium isotopes10,11. 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.

Decades ago, γ-ray observatories identified diffuse Galactic emission at 1.809 MeV (1-3) originating from β + decays of an isotope of aluminium, 26 Al, that has a mean-life time of 1.04 million years (4). Objects responsible for the production of this radioactive isotope have never been directly identified, owing to insufficient angular resolutions and sensitivities of the γ-ray observatories. Here, we report observations of millimetre-wave rotational lines of the isotopologue of aluminium monofluoride that contains the radioactive isotope ( 26 AlF). The emission is observed toward CK Vul which is thought to be a remnant of a stellar merger (5-7). Our constraints on the production of 26 Al combined with the estimates on the merger rate make it unlikely that objects similar to CK Vul are major producers of Galactic 26 Al. However, the observation may be a stepping stone for unambiguous identification of other Galactic sources of 26 Al. Moreover, a high content of 26

The ν lowest bending mode of linear C and of all its C-substituted isotopologues was recorded using a terahertz-supersonic jet spectrometer in combination with a laser ablation source. Sixty-five ro-vibrational transitions between 1.8 and 1.9 THz have been assigned to linear C12C12C12, C12C12C13, C12C13C12, C13C13C12, C13C12C13, and C13C13C13. For each isotopologue, molecular parameters were obtained and the C-C-bond length was derived experimentally. All results are in excellent agreement with recent ab initio calculations [B. Schröder and P. Sebald, J. Chem. Phys. 144, 044307 (2016)]. The new measurements explain why the interstellar search for singly substituted C12C12C13 has failed so far. A spectral line list with recommended transition frequencies based on global data fits is given to foster future interstellar detections.

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.

Context. Carbon molecules and their 13 C-isotopologues can be used to determine the 12 C/ 13 C abundance ratios in stellar and interstellar objects. C 3 is a pure carbon chain molecule found in star forming regions and in stellar shells of carbon-rich late-type stars. Latest laboratory data of 13 C-isotopologues of C 3 allow a selective search for the mono-substituted species 13 CCC and C 13 CC based on accurate ro-vibrational frequencies.Aims. Our aim was to provide the first detection of the 13 C-isotopologues 13 CCC and C 13 CC in space and to derive the 12 C/ 13 C ratio of interstellar gas in the massive star-forming region SgrB2(M) near the Galactic Center. Methods. We used the heterodyne receivers GREAT and upGREAT on board SOFIA to search for the ro-vibrational transitions Q(2) and Q(4) of 13 CCC and C 13 CC at 1.9 THz along the line of sight towards SgrB2(M). In addition, to determine the local excitation temperature we analyzed data from nine ro-vibrational transitions of the main isotopologue CCC in the frequency range between 1.6 -1.9 THz which were taken from the Herschel Science Data Archive. Results. We report the first detection of the isotopologues 13 CCC and C 13 CC. For both species the ro-vibrational absorption lines Q(2) and Q(4) have been identified, primarily arising from the warm gas physically associated with the strong continuum source SgrB2(M). From the available CCC ro-vibrational transitions we derived a gas excitation temperature of T ex = 44.4 +4.7 −3.9 K and a total column density of N(CCC)=3.88 +0.39 −0.35 × 10 15 cm −2 . Assuming the excitation temperatures of C 13 CC and 13 CCC to be the same as for CCC, we obtained column densities of the 13 C-isotopologues of N(C 13 CC) = 2.1 +0.9 −0.6 × 10 14 cm −2 and N( 13 CCC)=2.4 +1.2 −0.8 × 10 14 cm −2 . The derived 12 C/ 13 C abundance ratio in the C 3 molecules is 20.5±4.2, which is in agreement with the elemental ratio of 20, typically observed in SgrB2(M). However, we find the N( 13 CCC) / N(C 13 CC) ratio to be 1.2±0.1, which is shifted from the statistically expected value of 2. We propose that the discrepant abundance ratio arises due to the lower zero-point energy of C 13 CC which makes positionexchange reaction converting 13 CCC to C 13 CC energetically favorable.