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We present pure rotational transitions of the rare iron monoxide isotopologues. 57 F e 16 O , 58 F e 16 O and 56 F e 18 O in their lowest spin states 5 Δ 4 . For 57 F e 16 O , the rotational spectrum reveals hyperfine splitting due to the nuclear spin of I ( 57 F e) = 1 / 2. 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 parameters Δ U 01 F e = − 9.886 (24) and Δ U 01 O = − 10.761 (67) and the corresponding equilibrium bond length of r e B O = 1.6160302 (20) 10 − 10 m . With these new accurate molecular parameters line positions on a sub-MHz accuracy level can be calculated, including those of the radioactive isotopologue 60 F e 16 O . The new data allow for an astronomical search for the rare F e O isotopologues using sensitive radio telescopes, like the Atacama Large Millimetre/submillimetre Array. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • High-resolution absorption spectra of 6 TiO isotopologues between 240 and 380 GHz. • Mass-independent Dunham parametrization. • Determination of the molecular bond length r e BO = 1.62009060(31) Å with sub-fm accuracy. • Accurate 44TiO molecular parameters. • Analysis of fine- and hyperfine-structure reveals insight to the electronic structure. Abstract More than 130 pure rotational transitions of 46TiO, 47TiO, 48TiO, 49TiO, 50TiO, and 48Ti18O are recorded using a high-resolution mm-wave supersonic jet spectrometer in combination with a laser ablation source. For the first time a mass-independent Dunham-like analysis is performed encompassing rare titanium monoxide isotopologues, and are compared to results from high-accuracy quantum-chemical calculations. The obtained parametrization reveals for titanium monoxide effects due to deviations from the Born-Oppenheimer approximation. Additionally, the dominant titanium properties enable an insight into the electronic structure of TiO by analyzing its hyperfine interactions. Further, based on the mass-independent analysis, the frequency positions of the pure rotational transitions of the short lived rare isotopologue 44TiO are predicted with high accuracy, i.e., on a sub-MHz uncertainty level. This allows for dedicated radio-astronomical searches of this species in core-collapse environments of supernovae. [ABSTRACT FROM AUTHOR]

Pure rotational transitions of 27 Al 16 O, 27 Al 18 O, 27 Al 32 S, and 27 Al 34 S are recorded in the vibrational ground state and singly excited vibrational state using a mm-wavelength supersonic jet spectrometer in combination with a laser ablation source. In total 275 rotational transitions have been assigned. For the first time, mass-independent expanded Dunham analyses are performed using isotopologues of aluminum monoxide and aluminum monosulfide. The breakdown of the Born-Oppenheimer approximation is observed. Based on these mass-independent analyses, frequency positions of pure rotational transitions of the rare radioactive isotopologues 26 AlO and 26 AlS are predicted with uncertainties at the sub-MHz level. These data will allow to search for 26 Al-species in astrophysical environments using submm-observation facilities. [ABSTRACT FROM AUTHOR]

[Display omitted] • The infrared spectrum around 10 μm of titanium monoxide (TiO). • Spectra of isotopologues and vibrational hotbands. • A refined mass-independent Dunham analysis of the electronic ground-state. • Accurate line list for future astronomical observations. • Revision of vibrational transition matrix elements. 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 48TiO 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 γ and the Born–Oppenheimer correction coefficient Δ U 10 Ti for the first time. The parameter set enables to calculate the Born–Oppenheimer correction coefficients Δ U 02 Ti and Δ U 02 O . In addition, the vibrational transition moments for the observed vibrational transitions are reported. [ABSTRACT FROM AUTHOR]

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 r 0 , r s , and r m. However, for the C 3 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 ν 2 bending vibration of C 3. 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 A 0 = ν 2 2. This value is then used in the evaluation of r m , rather than assuming the molecule is linear. We test this approximation for A 0 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. Image 1 • Linear molecules are effectively bent in the ground vibrational state. • The effective rotational constant A 0 of a linear molecule is approximately a half of the bending vibrational frequency. • The r 0 -structure of C 3 is bent about 23° and even that of CO 2 is bent by 8°. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]