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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]

Abstract: The pure rotational spectrum driven by the small dipole moment produced perpendicular to the symmetry axis by centrifugal distortion has been investigated for CH3SiF3 in the ground vibrational state using a Fourier transform waveguide spectrometer. Between 10.9 and 17.0GHz, four (k +3← k) series in the Q branch have been measured in the lowest torsional state v 6 =0 for k =4, 5, 6, and 7 with 54⩽ J ⩽65. In each transition, the quantum number σ =0, +1, −1 labelling the different torsional sub-levels is conserved. For given (J,k), splittings from ∼10 to ∼45MHz have been observed between lines with different values of σ. The global data set includes the anticrossing molecular beam energy differences of [W.L. Meerts, I. Ozier, Chem. Phys. 71 (1982) 401–415] as well as the mm-wave R branch frequencies and (A 1 − A 2) splittings of [P. Dréan, J.-M. Colmont, J. Demaison, L. Dore, C. Degli Esposti, J. Mol. Spectrosc. 176 (1996) 23–27]). A good fit was obtained by varying 15 molecular parameters characterizing the torsion–rotation Hamiltonian H TR for the vibrational ground state. Because of the strong correlation between two of the quartic torsion–distortion parameters (F 0,3K and D 0,Km ) and a redundancy connecting the centrifugal distortion constants, four models were obtained yielding comparable fits. In each case, effective values were determined for the A-rotational constant and the height of the potential hindering the internal rotation. A high precision determination of the structural parameter ρ was made that is the same in all four models. For the off-diagonal quartic centrifugal distortion constant ε 0 and the sextic constants H 0,J , H 0,JK , H 0,KJ , and h 0,3, the differences in the values obtained in the two different reductions used have been explained in terms of the redundancy connecting these parameters. For σ =0, +1, −1, the energy level pattern for (|k|=3) is discussed for the case where the pure torsional energy splitting and the matrix elements off-diagonal in k are of comparable magnitude. A method is described of using an R branch study of the resulting σ-splittings for (|k|=3) to probe the zeroth-order torsional Hamiltonian. [Copyright &y& Elsevier]

Abstract: A pulsed ENDOR spectrometer operating at a microwave frequency of 275GHz is described. The results demonstrate that this type of spectroscopy can now be performed routinely at this high microwave frequency. The advantages compared to conventional EPR frequencies are the high spectral resolution, time resolution, and sensitivity. [Copyright &y& Elsevier]